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1.  Adult height and the risk of cause-specific death and vascular morbidity in 1 million people: individual participant meta-analysis 
Wormser, David | Angelantonio, Emanuele Di | Kaptoge, Stephen | Wood, Angela M | Gao, Pei | Sun, Qi | Walldius, Göran | Selmer, Randi | Verschuren, WM Monique | Bueno-de-Mesquita, H Bas | Engström, Gunnar | Ridker, Paul M | Njølstad, Inger | Iso, Hiroyasu | Holme, Ingar | Giampaoli, Simona | Tunstall-Pedoe, Hugh | Gaziano, J Michael | Brunner, Eric | Kee, Frank | Tosetto, Alberto | Meisinger, Christa | Brenner, Hermann | Ducimetiere, Pierre | Whincup, Peter H | Tipping, Robert W | Ford, Ian | Cremer, Peter | Hofman, Albert | Wilhelmsen, Lars | Clarke, Robert | de Boer, Ian H | Jukema, J Wouter | Ibañez, Alejandro Marín | Lawlor, Debbie A | D'Agostino, Ralph B | Rodriguez, Beatriz | Casiglia, Edoardo | Stehouwer, Coen DA | Simons, Leon A | Nietert, Paul J | Barrett-Connor, Elizabeth | Panagiotakos, Demosthenes B | Björkelund, Cecilia | Strandberg, Timo E | Wassertheil-Smoller, Sylvia | Blazer, Dan G | Meade, Tom W | Welin, Lennart | Svärdsudd, Kurt | Woodward, Mark | Nissinen, Aulikki | Kromhout, Daan | Jørgensen, Torben | Tilvis, Reijo S | Guralnik, Jack M | Rosengren, Annika | Taylor, James O | Kiechl, Stefan | Dagenais, Gilles R | Gerry, F | Fowkes, R | Wallace, Robert B | Khaw, Kay-Tee | Shaffer, Jonathan A | Visser, Marjolein | Kauhanen, Jussi | Salonen, Jukka T | Gallacher, John | Ben-Shlomo, Yoav | Kitamura, Akihiko | Sundström, Johan | Wennberg, Patrik | Kiyohara, Yutaka | Daimon, Makoto | de la Cámara, Agustin Gómez | Cooper, Jackie A | Onat, Altan | Devereux, Richard | Mukamal, Kenneth J | Dankner, Rachel | Knuiman, Matthew W | Crespo, Carlos J | Gansevoort, Ron T | Goldbourt, Uri | Nordestgaard, Børge G | Shaw, Jonathan E | Mussolino, Michael | Nakagawa, Hidaeki | Fletcher, Astrid | Kuller, Lewis H | Gillum, Richard F | Gudnason, Vilmundur | Assmann, Gerd | Wald, Nicholas | Jousilahti, Pekka R | Greenland, Philip | Trevisan, Maurizio | Ulmer, Hanno | Butterworth, Adam S | Folsom, Aaron R | Davey-Smith, George | Hu, Frank B | Danesh, John | Tipping, Robert W | Ford, Charles E | Simpson, Lara M | Walldius, Göran | Jungner, Ingmar | Folsom, Aaron R | Demerath, Ellen W | Franceschini, Nora | Lutsey, Pamela L | Panagiotakos, Demosthenes B | Pitsavos, Christos | Chrysohoou, Christina | Stefanadis, Christodoulos | Shaw, Jonathan E | Atkins, Robert | Zimmet, Paul Z | Barr, Elizabeth LM | Knuiman, Matthew W | Whincup, Peter H | Wannamethee, S Goya | Morris, Richard W | Willeit, Johann | Kiechl, Stefan | Weger, Siegfried | Oberhollenzer, Friedrich | Wald, Nicholas | Ebrahim, Shah | Lawlor, Debbie A | Gallacher, John | Ben-Shlomo, Yoav | Yarnell, John WG | Casiglia, Edoardo | Tikhonoff, Valérie | Greenland, Philip | Shay, Christina M | Garside, Daniel B | Nietert, Paul J | Sutherland, Susan E | Bachman, David L | Keil, Julian E | de Boer, Ian H | Kizer, Jorge R | Psaty, Bruce M | Mukamal, Kenneth J | Nordestgaard, Børge G | Tybjærg-Hansen, Anne | Jensen, Gorm B | Schnohr, Peter | Giampaoli, Simona | Palmieri, Luigi | Panico, Salvatore | Pilotto, Lorenza | Vanuzzo, Diego | de la Cámara, Agustin Gómez | Simons, Leon A | Simons, Judith | McCallum, John | Friedlander, Yechiel | Gerry, F | Fowkes, R | Price, Jackie F | Lee, Amanda J | Taylor, James O | Guralnik, Jack M | Phillips, Caroline L | Wallace, Robert B | Kohout, Frank J | Cornoni-Huntley, Joan C | Guralnik, Jack M | Blazer, Dan G | Guralnik, Jack M | Phillips, Caroline L | Phillips, Caroline L | Guralnik, Jack M | Khaw, Kay-Tee | Wareham, Nicholas J | Brenner, Hermann | Schöttker, Ben | Müller, Heiko | Rothenbacher, Dietrich | Wennberg, Patrik | Jansson, Jan-Håkan | Nissinen, Aulikki | Donfrancesco, Chiara | Giampaoli, Simona | Woodward, Mark | Vartiainen, Erkki | Jousilahti, Pekka R | Harald, Kennet | Salomaa, Veikko | D'Agostino, Ralph B | Vasan, Ramachandran S | Fox, Caroline S | Pencina, Michael J | Daimon, Makoto | Oizumi, Toshihide | Kayama, Takamasa | Kato, Takeo | Bladbjerg, Else-Marie | Jørgensen, Torben | Møller, Lars | Jespersen, Jørgen | Dankner, Rachel | Chetrit, Angela | Lubin, Flora | Svärdsudd, Kurt | Eriksson, Henry | Welin, Lennart | Lappas, Georgios | Rosengren, Annika | Lappas, Georgios | Welin, Lennart | Svärdsudd, Kurt | Eriksson, Henry | Lappas, Georgios | Bengtsson, Calle | Lissner, Lauren | Björkelund, Cecilia | Cremer, Peter | Nagel, Dorothea | Strandberg, Timo E | Salomaa, Veikko | Tilvis, Reijo S | Miettinen, Tatu A | Tilvis, Reijo S | Strandberg, Timo E | Kiyohara, Yutaka | Arima, Hisatomi | Doi, Yasufumi | Ninomiya, Toshiharu | Rodriguez, Beatriz | Dekker, Jacqueline M | Nijpels, Giel | Stehouwer, Coen DA | Hu, Frank B | Sun, Qi | Rimm, Eric B | Willett, Walter C | Iso, Hiroyasu | Kitamura, Akihiko | Yamagishi, Kazumasa | Noda, Hiroyuki | Goldbourt, Uri | Vartiainen, Erkki | Jousilahti, Pekka R | Harald, Kennet | Salomaa, Veikko | Kauhanen, Jussi | Salonen, Jukka T | Kurl, Sudhir | Tuomainen, Tomi-Pekka | Poppelaars, Jan L | Deeg, Dorly JH | Visser, Marjolein | Meade, Tom W | De Stavola, Bianca Lucia | Hedblad, Bo | Nilsson, Peter | Engström, Gunnar | Verschuren, WM Monique | Blokstra, Anneke | de Boer, Ian H | Shea, Steven J | Meisinger, Christa | Thorand, Barbara | Koenig, Wolfgang | Döring, Angela | Verschuren, WM Monique | Blokstra, Anneke | Bueno-de-Mesquita, H Bas | Wilhelmsen, Lars | Rosengren, Annika | Lappas, Georgios | Fletcher, Astrid | Nitsch, Dorothea | Kuller, Lewis H | Grandits, Greg | Tverdal, Aage | Selmer, Randi | Nystad, Wenche | Mussolino, Michael | Gillum, Richard F | Hu, Frank B | Sun, Qi | Manson, JoAnn E | Rimm, Eric B | Hankinson, Susan E | Meade, Tom W | De Stavola, Bianca Lucia | Cooper, Jackie A | Bauer, Kenneth A | Davidson, Karina W | Kirkland, Susan | Shaffer, Jonathan A | Shimbo, Daichi | Kitamura, Akihiko | Iso, Hiroyasu | Sato, Shinichi | Holme, Ingar | Selmer, Randi | Tverdal, Aage | Nystad, Wenche | Nakagawa, Hidaeki | Miura, Katsuyuki | Sakurai, Masaru | Ducimetiere, Pierre | Jouven, Xavier | Bakker, Stephan JL | Gansevoort, Ron T | van der Harst, Pim | Hillege, Hans L | Crespo, Carlos J | Garcia-Palmieri, Mario R | Kee, Frank | Amouyel, Philippe | Arveiler, Dominique | Ferrières, Jean | Schulte, Helmut | Assmann, Gerd | Jukema, J Wouter | de Craen, Anton JM | Sattar, Naveed | Stott, David J | Cantin, Bernard | Lamarche, Benoît | Després, Jean-Pierre | Dagenais, Gilles R | Barrett-Connor, Elizabeth | Bergstrom, Jaclyn | Bettencourt, Richele R | Buisson, Catherine | Gudnason, Vilmundur | Aspelund, Thor | Sigurdsson, Gunnar | Thorsson, Bolli | Trevisan, Maurizio | Hofman, Albert | Ikram, M Arfan | Tiemeier, Henning | Witteman, Jacqueline CM | Tunstall-Pedoe, Hugh | Tavendale, Roger | Lowe, Gordon DO | Woodward, Mark | Devereux, Richard | Yeh, Jeun-Liang | Ali, Tauqeer | Calhoun, Darren | Ben-Shlomo, Yoav | Davey-Smith, George | Onat, Altan | Can, Günay | Nakagawa, Hidaeki | Sakurai, Masaru | Nakamura, Koshi | Morikawa, Yuko | Njølstad, Inger | Mathiesen, Ellisiv B | Løchen, Maja-Lisa | Wilsgaard, Tom | Sundström, Johan | Ingelsson, Erik | Michaëlsson, Karl | Cederholm, Tommy | Gaziano, J Michael | Buring, Julie | Ridker, Paul M | Gaziano, J Michael | Ridker, Paul M | Ulmer, Hanno | Diem, Günter | Concin, Hans | Rodeghiero, Francesco | Tosetto, Alberto | Wassertheil-Smoller, Sylvia | Manson, JoAnn E | Marmot, Michael | Clarke, Robert | Fletcher, Astrid | Brunner, Eric | Shipley, Martin | Kivimaki, Mika | Ridker, Paul M | Buring, Julie | Ford, Ian | Robertson, Michele | Ibañez, Alejandro Marín | Feskens, Edith | Geleijnse, Johanna M | Kromhout, Daan | Walker, Matthew | Watson, Sarah | Alexander, Myriam | Butterworth, Adam S | Angelantonio, Emanuele Di | Franco, Oscar H | Gao, Pei | Gobin, Reeta | Haycock, Philip | Kaptoge, Stephen | Seshasai, Sreenivasa R Kondapally | Lewington, Sarah | Pennells, Lisa | Rapsomaniki, Eleni | Sarwar, Nadeem | Thompson, Alexander | Thompson, Simon G | Walker, Matthew | Watson, Sarah | White, Ian R | Wood, Angela M | Wormser, David | Zhao, Xiaohui | Danesh, John
Background The extent to which adult height, a biomarker of the interplay of genetic endowment and early-life experiences, is related to risk of chronic diseases in adulthood is uncertain.
Methods We calculated hazard ratios (HRs) for height, assessed in increments of 6.5 cm, using individual–participant data on 174 374 deaths or major non-fatal vascular outcomes recorded among 1 085 949 people in 121 prospective studies.
Results For people born between 1900 and 1960, mean adult height increased 0.5–1 cm with each successive decade of birth. After adjustment for age, sex, smoking and year of birth, HRs per 6.5 cm greater height were 0.97 (95% confidence interval: 0.96–0.99) for death from any cause, 0.94 (0.93–0.96) for death from vascular causes, 1.04 (1.03–1.06) for death from cancer and 0.92 (0.90–0.94) for death from other causes. Height was negatively associated with death from coronary disease, stroke subtypes, heart failure, stomach and oral cancers, chronic obstructive pulmonary disease, mental disorders, liver disease and external causes. In contrast, height was positively associated with death from ruptured aortic aneurysm, pulmonary embolism, melanoma and cancers of the pancreas, endocrine and nervous systems, ovary, breast, prostate, colorectum, blood and lung. HRs per 6.5 cm greater height ranged from 1.26 (1.12–1.42) for risk of melanoma death to 0.84 (0.80–0.89) for risk of death from chronic obstructive pulmonary disease. HRs were not appreciably altered after further adjustment for adiposity, blood pressure, lipids, inflammation biomarkers, diabetes mellitus, alcohol consumption or socio-economic indicators.
Conclusion Adult height has directionally opposing relationships with risk of death from several different major causes of chronic diseases.
doi:10.1093/ije/dys086
PMCID: PMC3465767  PMID: 22825588
Height; cardiovascular disease; cancer; cause-specific mortality; epidemiological study; meta-analysis
2.  Partner smoking and maternal cotinine during pregnancy: Implications for negative control methods☆ 
Drug and Alcohol Dependence  2014;139(100):159-163.
Background
Comparison of the associations of maternal and mother's partner smoking with offspring outcomes is, in theory, a useful method for assessing whether there may be an intrauterine effect of tobacco exposure on these outcomes. However, this approach assumes that the effects of passive smoking from exposure to partner smoking during pregnancy are minimal. We evaluated this assumption using a biochemical measure of tobacco exposure in pregnant women.
Methods
Cotinine levels taken during the first trimester of pregnancy were measured in a sample of 3928 women from the Avon Longitudinal Study of Parents and Children. Median cotinine values were compared across categories of smoking heaviness (cigarettes per day) of the women during the first trimester and in non-smoking women by the smoking heaviness of their partner.
Results
Cotinine levels were substantially higher in women who smoked compared to non-smokers (range of medians across smoking heaviness categories: 900–5362 ng/ml versus 20 ng/ml, interquartile range (IQR) (0–63) for non-smokers). In contrast, cotinine levels in non-smoking women were only very weakly related to partner smoking status (range of medians in women with smoking partners: 34–69 ng/ml versus 12 ng/ml, IQR (0–48) in women with non-smoking partners).
Conclusions
Levels of tobacco exposure from partner smoking, as assessed by cotinine, were low in non-smoking pregnant women. This suggests that using mother's partner's smoking as a negative control for investigating intrauterine effects is valid.
doi:10.1016/j.drugalcdep.2014.03.012
PMCID: PMC4026952  PMID: 24726428
ALSPAC; Cigarette smoking; Pregnancy; Intrauterine exposure; Negative control
3.  Life-course determinants of bone mass in young adults from a transitional rural community in India: the Andhra Pradesh Children and Parents Study (APCAPS)123 
Background: Undernutrition and physical inactivity are both associated with lower bone mass.
Objective: This study aimed to investigate the combined effects of early-life undernutrition and urbanized lifestyles in later life on bone mass accrual in young adults from a rural community in India that is undergoing rapid socioeconomic development.
Design: This was a prospective cohort study of participants of the Hyderabad Nutrition Trial (1987–1990), which offered balanced protein-calorie supplementation to pregnant women and preschool children younger than 6 y in the intervention villages. The 2009–2010 follow-up study collected data on current anthropometric measures, bone mineral density (BMD) measured by dual-energy X-ray absorptiometry, blood samples, diet, physical activity, and living standards of the trial participants (n = 1446, aged 18–23 y).
Results: Participants were generally lean and had low BMD [mean hip BMD: 0.83 (women), 0.95 (men) g/cm2; lumbar spine: 0.86 (women), 0.93 (men) g/cm2]. In models adjusted for current risk factors, no strong evidence of a positive association was found between BMD and early-life supplementation. On the other hand, current lean mass and weight-bearing physical activity were positively associated with BMD. No strong evidence of an association was found between BMD and current serum 25-hydroxyvitamin D or dietary intake of calcium, protein, or calories.
Conclusions: Current lean mass and weight-bearing physical activity were more important determinants of bone mass than was early-life undernutrition in this population. In transitional rural communities from low-income countries, promotion of physical activity may help to mitigate any potential adverse effects of early nutritional disadvantage.
doi:10.3945/ajcn.113.068791
PMCID: PMC4021785  PMID: 24695898
4.  Apolipoprotein E genotype, cardiovascular biomarkers and risk of stroke: Systematic review and meta-analysis of 14 015 stroke cases and pooled analysis of primary biomarker data from up to 60 883 individuals 
Background At the APOE gene, encoding apolipoprotein E, genotypes of the ε2/ε3/ε4 alleles associated with higher LDL-cholesterol (LDL-C) levels are also associated with higher coronary risk. However, the association of APOE genotype with other cardiovascular biomarkers and risk of ischaemic stroke is less clear. We evaluated the association of APOE genotype with risk of ischaemic stroke and assessed whether the observed effect was consistent with the effects of APOE genotype on LDL-C or other lipids and biomarkers of cardiovascular risk.
Methods We conducted a systematic review of published and unpublished studies reporting on APOE genotype and ischaemic stroke. We pooled 41 studies (with a total of 9027 cases and 61 730 controls) using a Bayesian meta-analysis to calculate the odds ratios (ORs) for ischaemic stroke with APOE genotype. To better evaluate potential mechanisms for any observed effect, we also conducted a pooled analysis of primary data using 16 studies (up to 60 883 individuals) of European ancestry. We evaluated the association of APOE genotype with lipids, other circulating biomarkers of cardiovascular risk and carotid intima-media thickness (C-IMT).
Results The ORs for association of APOE genotypes with ischaemic stroke were: 1.09 (95% credible intervals (CrI): 0.84–1.43) for ε2/ε2; 0.85 (95% CrI: 0.78–0.92) for ε2/ε3; 1.05 (95% CrI: 0.89–1.24) for ε2/ε4; 1.05 (95% CrI: 0.99–1.12) for ε3/ε4; and 1.12 (95% CrI: 0.94–1.33) for ε4/ε4 using the ε3/ε3 genotype as the reference group. A regression analysis that investigated the effect of LDL-C (using APOE as the instrument) on ischaemic stroke showed a positive dose-response association with an OR of 1.33 (95% CrI: 1.17, 1.52) per 1 mmol/l increase in LDL-C. In the separate pooled analysis, APOE genotype was linearly and positively associated with levels of LDL-C (P-trend: 2 × 10−152), apolipoprotein B (P-trend: 8.7 × 10−06) and C-IMT (P-trend: 0.001), and negatively and linearly associated with apolipoprotein E (P-trend: 6 × 10−26) and HDL-C (P-trend: 1.6 × 10−12). Associations with lipoprotein(a), C-reactive protein and triglycerides were non-linear.
Conclusions In people of European ancestry, APOE genotype showed a positive dose-response association with LDL-C, C-IMT and ischaemic stroke. However, the association of APOE ε2/ε2 genotype with ischaemic stroke requires further investigation. This cross-domain concordance supports a causal role of LDL-C on ischaemic stroke.
doi:10.1093/ije/dyt034
PMCID: PMC3619955  PMID: 23569189
Stroke; lipids; apolipoprotein E; cardiovascular disease; systematic review; meta-analysis; biomarkers
5.  Assessing Causality in the Association between Child Adiposity and Physical Activity Levels: A Mendelian Randomization Analysis 
PLoS Medicine  2014;11(3):e1001618.
Here, Timpson and colleagues performed a Mendelian Randomization analysis to determine whether childhood adiposity causally influences levels of physical activity. The results suggest that increased adiposity causes a reduction in physical activity in children; however, this study does not exclude lower physical activity also leading to increasing adiposity.
Please see later in the article for the Editors' Summary
Background
Cross-sectional studies have shown that objectively measured physical activity is associated with childhood adiposity, and a strong inverse dose–response association with body mass index (BMI) has been found. However, few studies have explored the extent to which this association reflects reverse causation. We aimed to determine whether childhood adiposity causally influences levels of physical activity using genetic variants reliably associated with adiposity to estimate causal effects.
Methods and Findings
The Avon Longitudinal Study of Parents and Children collected data on objectively assessed activity levels of 4,296 children at age 11 y with recorded BMI and genotypic data. We used 32 established genetic correlates of BMI combined in a weighted allelic score as an instrumental variable for adiposity to estimate the causal effect of adiposity on activity.
In observational analysis, a 3.3 kg/m2 (one standard deviation) higher BMI was associated with 22.3 (95% CI, 17.0, 27.6) movement counts/min less total physical activity (p = 1.6×10−16), 2.6 (2.1, 3.1) min/d less moderate-to-vigorous-intensity activity (p = 3.7×10−29), and 3.5 (1.5, 5.5) min/d more sedentary time (p = 5.0×10−4). In Mendelian randomization analyses, the same difference in BMI was associated with 32.4 (0.9, 63.9) movement counts/min less total physical activity (p = 0.04) (∼5.3% of the mean counts/minute), 2.8 (0.1, 5.5) min/d less moderate-to-vigorous-intensity activity (p = 0.04), and 13.2 (1.3, 25.2) min/d more sedentary time (p = 0.03). There was no strong evidence for a difference between variable estimates from observational estimates. Similar results were obtained using fat mass index. Low power and poor instrumentation of activity limited causal analysis of the influence of physical activity on BMI.
Conclusions
Our results suggest that increased adiposity causes a reduction in physical activity in children and support research into the targeting of BMI in efforts to increase childhood activity levels. Importantly, this does not exclude lower physical activity also leading to increased adiposity, i.e., bidirectional causation.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
The World Health Organization estimates that globally at least 42 million children under the age of five are obese. The World Health Organization recommends that all children undertake at least one hour of physical activity daily, on the basis that increased physical activity will reduce or prevent excessive weight gain in children and adolescents. In practice, while numerous studies have shown that body mass index (BMI) shows a strong inverse correlation with physical activity (i.e., active children are thinner than sedentary ones), exercise programs specifically targeted at obese children have had only very limited success in reducing weight. The reasons for this are not clear, although environmental factors such as watching television and lack of exercise facilities are traditionally blamed.
Why Was This Study Done?
One of the reasons why obese children do not lose weight through exercise might be that being fat in itself leads to a decrease in physical activity. This is termed reverse causation, i.e., obesity causes sedentary behavior, rather than the other way around. The potential influence of environmental factors (e.g., lack of opportunity to exercise) makes it difficult to prove this argument. Recent research has demonstrated that specific genotypes are related to obesity in children. Specific variations within the DNA of individual genes (single nucleotide polymorphisms, or SNPs) are more common in obese individuals and predispose to greater adiposity across the weight distribution. While adiposity itself can be influenced by many environmental factors that complicate the interpretation of observed associations, at the population level, genetic variation is not related to the same factors, and over the life course cannot be changed. Investigations that exploit these properties of genetic associations to inform the interpretation of observed associations are termed Mendelian randomization studies. This research technique is used to reduce the influence of confounding environmental factors on an observed clinical condition. The authors of this study use Mendelian randomization to determine whether a genetic tendency towards high BMI and fat mass is correlated with reduced levels of physical activity in a large cohort of children.
What Did the Researchers Do and Find?
The researchers looked at a cohort of children from a large long-term health research project (the Avon Longitudinal Study of Parents and Children). BMI and total body fat were recorded. Total daily activity was measured via a small movement-counting device. In addition, the participants underwent genotyping to detect the presence of several SNPs known to be linked to obesity. For each child a total BMI allelic score was determined based on the number of obesity-related genetic variants carried by that individual. The association between obesity and reduced physical activity was then studied in two ways. Direct correlation between actual BMI and physical activity was measured (observational data). Separately, the link between BMI allelic score and physical activity was also determined (Mendelian randomization or instrumental variable analysis). The observational data showed that boys were more active than girls and had lower BMI. Across both sexes, a higher-than-average BMI was associated with lower daily activity. In genetic analyses, allelic score had a positive correlation with BMI, with one particular SNP being most strongly linked to high BMI and total fat mass. A high allelic score for BMI was also correlated with lower levels of daily physical activity. The authors conclude that children who are obese and have an inherent predisposition to high BMI also have a propensity to reduced levels of physical activity, which may compound their weight gain.
What Do These Findings Mean?
This study provides evidence that being fat is in itself a risk factor for low activity levels, separately from external environmental influences. This may be an example of “reverse causation,” i.e., high BMI causes a reduction in physical activity. Alternatively, there may be a bidirectional causality, so that those with a genetic predisposition to high fat mass exercise less, leading to higher BMI, and so on, in a vicious circle. A significant limitation of the study is that validated allelic scores for physical activity are not available. Thus, it is not possible to determine whether individuals with a high allelic score for BMI also have a propensity to exercise less, or whether it is simply the circumstance of being overweight that discourages activity. This study does suggest that trying to persuade obese children to lose weight by exercising more is likely to be ineffective unless additional strategies to reduce BMI, such as strict diet control, are also implemented.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001618.
The US Centers for Disease Control and Prevention provides obesity-related statistics, details of prevention programs, and an overview on public health strategy in the United States
A more worldwide view is given by the World Health Organization
The UK National Health Service website gives information on physical activity guidelines for different age groups
The International Obesity Task Force is a network of organizations that seeks to alert the world to the growing health crisis threatened by soaring levels of obesity
MedlinePlus—which brings together authoritative information from the US National Library of Medicine, National Institutes of Health, and other government agencies and health-related organizations—has a page on obesity
Additional information on the Avon Longitudinal Study of Parents and Children is available
The British Medical Journal has an article that describes Mendelian randomization
doi:10.1371/journal.pmed.1001618
PMCID: PMC3958348  PMID: 24642734
6.  Effects of promoting increased duration and exclusivity of breastfeeding on adiposity and insulin-like growth factor-I at age 11.5 years: a randomized trial 
Importance
Evidence that increased duration and exclusivity of breastfeeding reduces child obesity risk is based on observational studies that are prone to confounding.
Objective
To investigate effects of an intervention to promote increased duration and exclusivity of breastfeeding on child adiposity and circulating insulin-like growth factor (IGF)-I (which regulates growth).
Design
Cluster-randomized controlled trial.
Setting
31 Belarusian maternity hospitals and their affiliated polyclinics, randomized to usual practices (n=15) or a breastfeeding promotion intervention (n=16).
Participants
17,046 breastfeeding mother-infant pairs enrolled in 1996/7, of whom 13,879 (81.4%) were followed-up between January 2008 and December 2010 at a median age of 11.5 years.
Intervention
Breastfeeding promotion intervention modeled on the WHO/UNICEF Baby Friendly Hospital Initiative.
Main outcome measures
Body mass index (BMI), fat and fat-free mass indices (FMI and FFMI), percent body fat, waist circumference, triceps and subscapular skinfold thicknesses, overweight and obesity, and whole-blood IGF-I. Primary analysis was based on modified intention-to-treat (without imputation), accounting for clustering within hospitals/clinics.
Results
The experimental intervention substantially increased breastfeeding duration and exclusivity (43% vs. 6% and 7.9% vs. 0.6% exclusively breastfed at 3 and 6 months, respectively) versus the control intervention. Cluster-adjusted mean differences in outcomes at 11.5 years between experimental vs. control groups were: 0.19 kg/m2 (95% 4 CI: −0.09, 0.46) for BMI; 0.12 kg/m2 (−0.03, 0.28) for FMI; 0.04 kg/m2 (−0.11, 0.18) for FFMI; 0.47% (−0.11, 1.05) for % body fat; 0.30 cm (−1.41, 2.01) for waist circumference; −0.07 mm (−1.71, 1.57) for triceps and −0.02 mm (−0.79, 0.75) for subscapular skinfold thicknesses; and −0.02 standard deviations (−0.12, 0.08) for IGF-I. The cluster-adjusted odds ratio for overweight / obesity (BMI ≥85th percentile vs <85th percentile) was 1.18 (1.01, 1.39) and for obesity (BMI ≥95th vs <85th percentile) was 1.17 (0.97, 1.41).
Conclusions and relevance
Among healthy term infants in Belarus, an intervention that succeeded in improving the duration and exclusivity of breastfeeding did not prevent overweight or obesity, nor did it affect IGF-I levels, at age 11.5 years. Breastfeeding has many advantages, but population strategies to increase the duration and exclusivity of breastfeeding are unlikely to curb the obesity epidemic.
doi:10.1001/jama.2013.167
PMCID: PMC3752893  PMID: 23483175
Breast feeding; lactation; adiposity; body mass index; randomized controlled trial; insulin-like growth factor-1; childhood
7.  Personality, Behavior and Environmental Features Associated with OXTR Genetic Variants in British Mothers 
PLoS ONE  2014;9(3):e90465.
Background
It is assumed that the oxytocin receptor gene (OXTR) is associated with factors that are related to features of reproduction as well as the currently emerging fields of mood and emotional response.
Methods
We analysed data from over 8000 mothers who participated in the Avon Longitudinal Study of Parents and Children (ALSPAC). We determined reproductive, emotional and personality differences related to the two SNPs rs53576 and rs2254298 of the oxytocin receptor gene to determine whether there was evidence in this population for: (i) associations with emotional and personality differences, and (ii) behavioural or environmental links with these SNPs using a hypothesis free approach with over 1000 types of exposure.
Results
Our analyses of 7723 women showed that there were no differences in 11 mood, social or relationship characteristics associated with the rs2254298, and just one with rs53576 (with emotional loneliness) – one statistically significant out of 22 tests is no more than would be expected by chance. There were no interactions with childhood abuse. Using a hypothesis-free approach we found few indicators of environmental or behavioural differences associated with rs2254298, but there was an excess of associations with eating habits with rs53576. The findings included an association with dieting to lose weight, and habits typical of bulimia for the women with GG. The nutrition of the women also showed negative associations of the GG genotype with 13 nutrients, including vitamins D, B12 and retinol, and intake of calcium, potassium and iodine.
Conclusions
We conclude that this large database of pregnant women was unable to provide confirmation of the types of personality associated with these two OXTR SNPs, but we have shown some evidence of eating differences in those with GG on rs53576. Confirmation of our hypothesis free associations using other data sets is important.
doi:10.1371/journal.pone.0090465
PMCID: PMC3951216  PMID: 24621820
8.  The Association of Early Life Supplemental Nutrition With Lean Body Mass and Grip Strength in Adulthood: Evidence From APCAPS 
American Journal of Epidemiology  2014;179(6):700-709.
In the present study, we examined the associations of early nutrition with adult lean body mass (LBM) and muscle strength in a birth cohort that was established to assess the long-term impact of a nutrition program. Participants (n = 1,446, 32% female) were born near Hyderabad, India, in 29 villages from 1987 to 1990, during which time only intervention villages (n = 15) had a government program that offered balanced protein-calorie supplementation to pregnant women and children. Participants’ LBM and appendicular skeletal muscle mass were measured using dual energy x-ray absorptiometry; grip strength and information on lifestyle indicators, including diet and physical activity level, were also obtained. Ages (mean = 20.3 years) and body mass indexes (weight (kg)/height (m)2; mean = 19.5) of participants in 2 groups were similar. Current dietary energy intake was higher in the intervention group. Unadjusted LBM and grip strength were similar in 2 groups. After adjustment for potential confounders, the intervention group had lower LBM (β = −0.75; P = 0.03), appendicular skeletal muscle mass, and grip strength than did controls, but these differences were small in magnitude (<0.1 standard deviation). Multivariable regression analyses showed that current socioeconomic position, energy intake, and physical activity level had a positive association with adult LBM and muscle strength. This study could not detect a “programming” effect of early nutrition supplementation on adult LBM and muscle strength.
doi:10.1093/aje/kwt332
PMCID: PMC3939852  PMID: 24553777
body composition; cohort study; developmental origins of health and disease; grip strength; lean body mass; muscle mass; nutrition; physical activity
9.  Is the Growth of the Fetus of a Non-Smoking Mother Influenced by the Smoking of Either Grandmother while Pregnant? 
PLoS ONE  2014;9(2):e86781.
Background
There are animal data that indicate that prenatal environmental exposures have sex-specific effects on subsequent generations. In humans, an increase in birthweight has been reported if the maternal grandmother had smoked in the pregnancy giving rise to the mother. Here we assess whether prenatal exposure of either parent to cigarette smoke has a sex-specific effect on the grandchild's birth measurements.
Methods
Information from 12707 maternal and 9677 paternal grandmothers of children in the Avon Longitudinal Study of Parents and Children (ALSPAC) concerned whether they had smoked while expecting the study parent. Study children were weighed and measured at birth. Analyses to test effects of grandmaternal prenatal smoking used multiple regression allowing for several potential confounders; analyses were restricted to births to non-smoking study mothers.
Findings
After adjustment, the average birthweight, birth length and BMI measurements of the grandsons (but not granddaughters) were greater if the maternal grandmother smoked prenatally: birthweight  = +61 [95% CI +30, +92] g; birth length  = +0·19 [95% CI +0·02, +0·35] cm; BMI  = +1·6 [95% CI +0·6, +2·6] g/m2. Similar effects were seen in births to primiparae and multiparae. Additional allowance for maternal birthweight resulted in an average increase in boys to +100 g [95% CI +61, +140] g. There were no fetal growth differences if the paternal grandmother had smoked prenatally.
Conclusions
The evidence from this study suggests that when the mother does not smoke in pregnancy the maternal grandmother's smoking habit in pregnancy has a positive association with her grandson's fetal growth.
doi:10.1371/journal.pone.0086781
PMCID: PMC3913581  PMID: 24504157
10.  Differences in smoking associated DNA methylation patterns in South Asians and Europeans 
Clinical Epigenetics  2014;6(1):4.
Background
DNA methylation is strongly associated with smoking status at multiple sites across the genome. Studies have largely been restricted to European origin individuals yet the greatest increase in smoking is occurring in low income countries, such as the Indian subcontinent. We determined whether there are differences between South Asians and Europeans in smoking related loci, and if a smoking score, combining all smoking related DNA methylation scores, could differentiate smokers from non-smokers.
Results
Illumina HM450k BeadChip arrays were performed on 192 samples from the Southall And Brent REvisited (SABRE) cohort. Differential methylation in smokers was identified in 29 individual CpG sites at 18 unique loci. Interaction between smoking status and ethnic group was identified at the AHRR locus. Ethnic differences in DNA methylation were identified in non-smokers at two further loci, 6p21.33 and GNG12. With the exception of GFI1 and MYO1G these differences were largely unaffected by adjustment for cell composition. A smoking score based on methylation profile was constructed. Current smokers were identified with 100% sensitivity and 97% specificity in Europeans and with 80% sensitivity and 95% specificity in South Asians.
Conclusions
Differences in ethnic groups were identified in both single CpG sites and combined smoking score. The smoking score is a valuable tool for identification of true current smoking behaviour. Explanations for ethnic differences in DNA methylation in association with smoking may provide valuable clues to disease pathways.
doi:10.1186/1868-7083-6-4
PMCID: PMC3915234  PMID: 24485148
DNA methylation; Smoking; Prediction; Ethnic differences; Epigenetic epidemiology
11.  MATERNAL COTYLEDONS AT BIRTH PREDICT BLOOD PRESSURE IN CHILDHOOD 
Placenta  2013;34(8):672-675.
Introduction
A small placental surface at birth has been shown to be associated with the development of hypertension in later life. In this study we extend this observation by looking at the relationship between the number of placental cotyledons and blood pressure in childhood. Because the number of cotyledons is correlated with the surface area, we hypothesized that fewer cotyledons would be associated with higher blood pressure.
Methods
The Alspac study is a longitudinal study of 13,971 children born in Bristol. Their placentas were stored in formalin. We photographed the placentas of a sample of the children and related the number of maternal cotyledons to their blood pressure levels at age 9 years.
Results
Contrary to our hypothesis, a greater number of maternal cotyledons was associated with higher blood pressure. Among boys, a greater number of cotyledons was associated with higher systolic and diastolic pressure but not with higher pulse pressure. Diastolic pressure rose by 2.2 mmHg (95% CI 0.6 to 3.7, p =0.007) for every 10 additional cotyledons. Among girls, a greater number of cotyledons was associated with higher systolic pressure and pulse pressure but not with higher diastolic pressure. Pulse pressure rose by 2.7 mmHg (1.1 to 4.3, p<0.001) for every 10 additional cotyledons. These associations were little changed by adjustment for placental surface area.
Conclusion
Our study has shown that a large number of maternal cotyledons is associated with raised blood pressure in childhood. The associations differ in the two sexes.
doi:10.1016/j.placenta.2013.04.019
PMCID: PMC3733167  PMID: 23731799
Alspac; maternal cotyledons; blood pressure
13.  Socio-Demographic Inequalities in the Prevalence, Diagnosis and Management of Hypertension in India: Analysis of Nationally-Representative Survey Data 
PLoS ONE  2014;9(1):e86043.
Background
Hypertension is a major contributing factor to the current epidemic of cardiovascular disease in India. Small studies suggest high, and increasing, prevalence especially in urban areas, with poor detection and management, but national data has been lacking. The aim of the current study was to use nationally-representative survey data to examine socio-demographic inequalities in the prevalence, diagnosis and management of hypertension in Indian adults.
Methods
Using data on self-reported diagnosis and treatment, and blood pressure measurement, collected from 12,198 respondents aged 18+ in the 2007 WHO Study on Global Ageing and Adult Health in India, factors associated with prevalence, diagnosis and treatment of hypertension were investigated.
Results
22% men and 26% women had hypertension; prevalence increased steeply with body mass index (<18.5 kg/m2: 18% men, 21% women; 25-29.9 kg/m2: 35% men, 35% women), was higher in the least poor vs. poorest (men: odds ratio (95%CI) 1.82 (1.20 to 2.76); women: 1.40 (1.08 to 1.81)), urban vs. rural men (1.64 (1.19 to 2.25)), and men recently vs. never using alcohol (1.96 (1.40 to 2.76)). Over half the hypertension in women, and 70% in men, was undetected with particularly poor detection rates in young urban men, and in poorer households. Two-thirds of men and women with detected hypertension were treated. Two-thirds of women treated had their hypertension controlled, irrespective of urban/rural setting or wealth. Adequate blood pressure control was sub-optimal in urban men.
Conclusion
Hypertension is very common in India, even among underweight adults and those of lower socioeconomic position. Improved detection is needed to reduce the burden of disease attributable to hypertension. Levels of treatment and control are relatively good, particularly in women, although urban men require more careful attention.
doi:10.1371/journal.pone.0086043
PMCID: PMC3900470  PMID: 24465859
14.  A recall-by-genotype study of CHRNA5-A3-B4 genotype, cotinine and smoking topography: study protocol 
BMC Medical Genetics  2014;15:13.
Background
Genome-wide association studies have revealed an association between several loci in the nicotinic acetylcholine receptor gene cluster CHRNA5-A3-B4 and daily cigarette consumption. Recent studies have sought to refine this phenotype, and have shown that a locus within this cluster, marked primarily by rs1051730 and rs16969968, is also associated with levels of cotinine, the primary metabolite of nicotine. This association remains after adjustment for self-reported smoking, which suggests that even amongst people who smoke the same number of cigarettes there is still genetically-influenced variation in nicotine consumption. This is likely to be due to differences in smoking topography, that is, how a cigarette is smoked (e.g., volume of smoke inhaled per puff, number of puffs taken per cigarette). The aim of this study is to determine potential mediation of the relationship between the rs1051730 locus and cotinine levels by smoking topography.
Methods/Design
Adopting a recall-by-genotype design, we will recruit 200 adults from the Avon Longitudinal Study of Parents and Children on the basis of minor or major homozygote status at rs1051730 (100 in each genotype group). All participants will be current, daily smokers. Our primary study outcome measures will be measures of smoking topography: total volume of smoke (ml) inhaled per cigarette, total volume of smoke (ml) inhaled over of the course of one day, and salivary cotinine level (ng/ml).
Discussion
This study will extend our understanding of the biological basis of inter-individual variability in heaviness of smoking, and therefore in exposure to smoking-related toxins. The novel recall-by-genotype approach we will use is efficient, maximising statistical power, and enables the collection of extremely precise phenotypic data that are impractical to collect in a larger sample. The methods described within this protocol also hold the potential for wider application in the field of molecular genetics.
doi:10.1186/1471-2350-15-13
PMCID: PMC3900674  PMID: 24451018
Smoking; Cotinine; Genetics; CHRNA3; CHRNA5; Smoking topography
15.  Prenatal alcohol exposure and childhood atopic disease: A Mendelian randomization approach☆ 
Background
Alcohol consumption in western pregnant women is not uncommon and could be a risk factor for childhood atopic disease. However, reported alcohol intake may be unreliable, and associations are likely to be confounded.
Objective
We aimed to study the relation between prenatal alcohol exposure and atopic phenotypes in a large population-based birth cohort with the use of a Mendelian randomization approach to minimize bias and confounding.
Methods
In white mothers and children in the Avon Longitudinal Study of Parents and Children (ALSPAC) we first analyzed associations between reported maternal alcohol consumption during pregnancy and atopic outcomes in the offspring measured at 7 years of age (asthma, wheezing, hay fever, eczema, atopy, and total IgE). We then analyzed the relation of maternal alcohol dehydrogenase (ADH)1B genotype (rs1229984) with these outcomes (the A allele is associated with faster metabolism and reduced alcohol consumption and, among drinkers, would be expected to reduce fetal exposure to ethanol).
Results
After controlling for confounders, reported maternal drinking in late pregnancy was negatively associated with childhood asthma and hay fever (adjusted odds ratio [OR] per category increase in intake: 0.91 [95% CI, 0.82-1.01] and 0.87 [95% CI, 0.78-0.98], respectively). However, maternal ADH1B genotype was not associated with asthma comparing carriers of A allele with persons homozygous for G allele (OR, 0.98 [95% CI, 0.66-1.47]) or hay fever (OR, 1.11 [95% CI, 0.71-1.72]), nor with any other atopic outcome.
Conclusion
We have found no evidence to suggest that prenatal alcohol exposure increases the risk of asthma or atopy in childhood.
doi:10.1016/j.jaci.2013.04.051
PMCID: PMC3884122  PMID: 23806636
Alcohol; ADH1B; Mendelian randomization; prenatal exposure; ALSPAC; pregnancy; birth cohort; asthma; atopy; ADH, Alcohol dehydrogenase; ALSPAC, Avon Longitudinal Study of Parents and Children (ALSPAC); GWAS, Genome Wide Association Study; PCA, Principal Components Analysis
16.  Effects of Nutritional Supplementation during Pregnancy on Early Adult Disease Risk: Follow Up of Offspring of Participants in a Randomised Controlled Trial Investigating Effects of Supplementation on Infant Birth Weight 
PLoS ONE  2013;8(12):e83371.
Background
Observational evidence suggests that improving fetal growth may improve adult health. Experimental evidence from nutritional supplementation trials undertaken amongst pregnant women in the less developed world does not show strong or consistent effects on adult disease risk and no trials from the more developed world have previously been reported.
Objective
To test the hypothesis that nutritional supplementation during pregnancy influences offspring disease risk in adulthood
Design
Clinical assessment of a range of established diseases risk markers in young adult offspring of 283 South Asian mothers who participated in two trials of nutritional supplementation during pregnancy (protein/energy/vitamins; energy/vitamins or vitamins only) at Sorrento Maternity Hospital in Birmingham UK either unselected or selected on the basis of nutritional status.
Results
236 (83%) offspring were traced and 118 (50%) of these were assessed in clinic. Protein/energy/vitamins supplementation amongst undernourished mothers was associated with increased infant birthweight. Nutritional supplementation showed no strong association with any one of a comprehensive range of markers of adult disease risk and no consistent pattern of association with risk across markers in offspring of either unselected or undernourished mothers.
Conclusions
We found no evidence that nutritional supplements given to pregnant women are an important influence on adult disease risk however our study lacked power to estimate small effects. Our findings do not provide support for a policy of nutritional supplementation for pregnant women as an effective means to improve adult health in more developed societies.
doi:10.1371/journal.pone.0083371
PMCID: PMC3862758  PMID: 24349496
17.  Association of a Body Mass Index Genetic Risk Score with Growth throughout Childhood and Adolescence 
PLoS ONE  2013;8(11):e79547.
Background
While the number of established genetic variants associated with adult body mass index (BMI) is growing, the relationships between these variants and growth during childhood are yet to be fully characterised. We examined the association between validated adult BMI associated single nucleotide polymorphisms (SNPs) and growth trajectories across childhood. We investigated the timing of onset of the genetic effect and whether it was sex specific.
Methods
Children from the ALSPAC and Raine birth cohorts were used for analysis (n = 9,328). Genotype data from 32 adult BMI associated SNPs were investigated individually and as an allelic score. Linear mixed effects models with smoothing splines were used for longitudinal modelling of the growth parameters and measures of adiposity peak and rebound were derived.
Results
The allelic score was associated with BMI growth throughout childhood, explaining 0.58% of the total variance in BMI in females and 0.44% in males. The allelic score was associated with higher BMI at the adiposity peak (females  =  0.0163 kg/m2 per allele, males  =  0.0123 kg/m2 per allele) and earlier age (-0.0362 years per allele in males and females) and higher BMI (0.0332 kg/m2 per allele in females and 0.0364 kg/m2 per allele in males) at the adiposity rebound. No gene:sex interactions were detected for BMI growth.
Conclusions
This study suggests that known adult genetic determinants of BMI have observable effects on growth from early childhood, and is consistent with the hypothesis that genetic determinants of adult susceptibility to obesity act from early childhood and develop over the life course.
doi:10.1371/journal.pone.0079547
PMCID: PMC3823612  PMID: 24244521
18.  KCTD8 Gene and Brain Growth in Adverse Intrauterine Environment: A Genome-wide Association Study 
Cerebral Cortex (New York, NY)  2011;22(11):2634-2642.
The most dramatic growth of the human brain occurs in utero and during the first 2 years of postnatal life. Genesis of the cerebral cortex involves cell proliferation, migration, and apoptosis, all of which may be influenced by prenatal environment. Here, we show that variation in KCTD8 (potassium channel tetramerization domain 8) is associated with brain size in female adolescents (rs716890, P = 5.40 × 10−09). Furthermore, we found that the KCTD8 locus interacts with prenatal exposure to maternal cigarette smoking vis-à-vis cortical area and cortical folding: In exposed girls only, the KCTD8 locus explains up to 21% of variance. Using head circumference as a proxy of brain size at 7 years of age, we have replicated this gene–environment interaction in an independent sample. We speculate that KCTD8 might modulate adverse effects of smoking during pregnancy on brain development via apoptosis triggered by low intracellular levels of potassium, possibly reducing the number of progenitor cells.
doi:10.1093/cercor/bhr350
PMCID: PMC3464418  PMID: 22156575
adolescence; brain; GWAS; pregnancy
19.  Mining the Human Phenome Using Allelic Scores That Index Biological Intermediates 
PLoS Genetics  2013;9(10):e1003919.
It is common practice in genome-wide association studies (GWAS) to focus on the relationship between disease risk and genetic variants one marker at a time. When relevant genes are identified it is often possible to implicate biological intermediates and pathways likely to be involved in disease aetiology. However, single genetic variants typically explain small amounts of disease risk. Our idea is to construct allelic scores that explain greater proportions of the variance in biological intermediates, and subsequently use these scores to data mine GWAS. To investigate the approach's properties, we indexed three biological intermediates where the results of large GWAS meta-analyses were available: body mass index, C-reactive protein and low density lipoprotein levels. We generated allelic scores in the Avon Longitudinal Study of Parents and Children, and in publicly available data from the first Wellcome Trust Case Control Consortium. We compared the explanatory ability of allelic scores in terms of their capacity to proxy for the intermediate of interest, and the extent to which they associated with disease. We found that allelic scores derived from known variants and allelic scores derived from hundreds of thousands of genetic markers explained significant portions of the variance in biological intermediates of interest, and many of these scores showed expected correlations with disease. Genome-wide allelic scores however tended to lack specificity suggesting that they should be used with caution and perhaps only to proxy biological intermediates for which there are no known individual variants. Power calculations confirm the feasibility of extending our strategy to the analysis of tens of thousands of molecular phenotypes in large genome-wide meta-analyses. We conclude that our method represents a simple way in which potentially tens of thousands of molecular phenotypes could be screened for causal relationships with disease without having to expensively measure these variables in individual disease collections.
Author Summary
The standard approach in genome-wide association studies is to analyse the relationship between genetic variants and disease one marker at a time. Significant associations between markers and disease are then used as evidence to implicate biological intermediates and pathways likely to be involved in disease aetiology. However, single genetic variants typically only explain small amounts of disease risk. Our idea is to construct allelic scores that explain greater proportions of the variance in biological intermediates than single markers, and then use these scores to data mine genome-wide association studies. We show how allelic scores derived from known variants as well as allelic scores derived from hundreds of thousands of genetic markers across the genome explain significant portions of the variance in body mass index, levels of C-reactive protein, and LDLc cholesterol, and many of these scores show expected correlations with disease. Power calculations confirm the feasibility of scaling our strategy to the analysis of tens of thousands of molecular phenotypes in large genome-wide meta-analyses. Our method represents a simple way in which tens of thousands of molecular phenotypes could be screened for potential causal relationships with disease.
doi:10.1371/journal.pgen.1003919
PMCID: PMC3814299  PMID: 24204319
20.  Effect of Prenatal Alcohol Exposure on Childhood Academic Outcomes: Contrasting Maternal and Paternal Associations in the ALSPAC Study 
PLoS ONE  2013;8(10):e74844.
Background
The impact of low-to-moderate levels of alcohol consumption during pregnancy on child cognitive outcomes has been of recent concern. This study has tested the hypothesis that low-to-moderate maternal alcohol use in pregnancy is associated with lower school test scores at age 11 in the offspring via intrauterine mechanisms.
Methods
We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a birth cohort study based in the South West of England. Analyses were conducted on 7062 participants who had complete data on: maternal and paternal patterns of alcohol use in the first trimester and at 18 weeks' gestation, child's academic outcomes measured at age 11, gender, maternal age, parity, marital status, ethnicity, household crowding, home ownership status and parental education. We contrasted the association of mother's alcohol consumption during pregnancy with child's National Curriculum Key Stage 2 (KS2) test scores with the association for father's alcohol consumption (during the time the mother was pregnant) with child's National Curriculum Key Stage 2 (KS2) test scores. We used multivariate linear regression to estimate mean differences and 95% confidence intervals [CI] in KS2 scores across the exposure categories and computed f statistics to compare maternal and paternal associations.
Findings and conclusions
Drinking up to 1 unit of alcohol a day during pregnancy was not associated with lower test scores. However, frequent prenatal consumption of 4 units (equivalent to 32 grams of alcohol) on each single drinking occasion was associated with reduced educational attainment [Mean change in offspring KS2 score was −0.68 (−1.03, −0.33) for maternal alcohol categories compared to 0.27 (0.07, 0.46) for paternal alcohol categories]. Frequent consumption of 4 units of alcohol during pregnancy may adversely affect childhood academic outcomes via intrauterine mechanisms.
doi:10.1371/journal.pone.0074844
PMCID: PMC3794033  PMID: 24130672
21.  Prenatal alcohol exposure and offspring cognition and school performance. A ‘Mendelian randomization’ natural experiment 
Background There is substantial debate as to whether moderate alcohol use during pregnancy could have subtle but important effects on offspring, by impairing later cognitive function and thus school performance. The authors aimed to investigate the unconfounded effect of moderately increased prenatal alcohol exposure on cognitive/educational performance.
Methods We used mother-offspring pairs participating in the Avon Longitudinal Study of Parents and Children (ALSPAC) and performed both conventional observational analyses and Mendelian randomization using an ADH1B variant (rs1229984) associated with reduced alcohol consumption. Women of White European origin with genotype and self-reported prenatal alcohol consumption, whose offspring’s IQ score had been assessed in clinic (N = 4061 pairs) or Key Stage 2 (KS2) academic achievement score was available through linkage to the National Pupil Database (N = 6268), contributed to the analyses.
Results Women reporting moderate drinking before and during early pregnancy were relatively affluent compared with women reporting lighter drinking, and their children had higher KS2 and IQ scores. In contrast, children whose mothers’ genotype predisposes to lower consumption or abstinence during early pregnancy had higher KS2 scores (mean difference +1.7, 95% confidence interval +0.4, +3.0) than children of mothers whose genotype predisposed to heavier drinking, after adjustment for population stratification.
Conclusions Better offspring cognitive/educational outcomes observed in association with prenatal alcohol exposure presumably reflected residual confounding by factors associated with social position and maternal education. The unconfounded Mendelian randomization estimates suggest a small but potentially important detrimental effect of small increases in prenatal alcohol exposure, at least on educational outcomes.
doi:10.1093/ije/dyt172
PMCID: PMC3807618  PMID: 24065783
Alcohol dehydrogenase; causality; cognition; confounding factors; educational measurement; ethanol; Mendelian randomization analysis; pregnancy
22.  GWAS of 126,559 Individuals Identifies Genetic Variants Associated with Educational Attainment 
Rietveld, Cornelius A. | Medland, Sarah E. | Derringer, Jaime | Yang, Jian | Esko, Tõnu | Martin, Nicolas W. | Westra, Harm-Jan | Shakhbazov, Konstantin | Abdellaoui, Abdel | Agrawal, Arpana | Albrecht, Eva | Alizadeh, Behrooz Z. | Amin, Najaf | Barnard, John | Baumeister, Sebastian E. | Benke, Kelly S. | Bielak, Lawrence F. | Boatman, Jeffrey A. | Boyle, Patricia A. | Davies, Gail | de Leeuw, Christiaan | Eklund, Niina | Evans, Daniel S. | Ferhmann, Rudolf | Fischer, Krista | Gieger, Christian | Gjessing, Håkon K. | Hägg, Sara | Harris, Jennifer R. | Hayward, Caroline | Holzapfel, Christina | Ibrahim-Verbaas, Carla A. | Ingelsson, Erik | Jacobsson, Bo | Joshi, Peter K. | Jugessur, Astanand | Kaakinen, Marika | Kanoni, Stavroula | Karjalainen, Juha | Kolcic, Ivana | Kristiansson, Kati | Kutalik, Zoltán | Lahti, Jari | Lee, Sang H. | Lin, Peng | Lind, Penelope A. | Liu, Yongmei | Lohman, Kurt | Loitfelder, Marisa | McMahon, George | Vidal, Pedro Marques | Meirelles, Osorio | Milani, Lili | Myhre, Ronny | Nuotio, Marja-Liisa | Oldmeadow, Christopher J. | Petrovic, Katja E. | Peyrot, Wouter J. | Polašek, Ozren | Quaye, Lydia | Reinmaa, Eva | Rice, John P. | Rizzi, Thais S. | Schmidt, Helena | Schmidt, Reinhold | Smith, Albert V. | Smith, Jennifer A. | Tanaka, Toshiko | Terracciano, Antonio | van der Loos, Matthijs J.H.M. | Vitart, Veronique | Völzke, Henry | Wellmann, Jürgen | Yu, Lei | Zhao, Wei | Allik, Jüri | Attia, John R. | Bandinelli, Stefania | Bastardot, François | Beauchamp, Jonathan | Bennett, David A. | Berger, Klaus | Bierut, Laura J. | Boomsma, Dorret I. | Bültmann, Ute | Campbell, Harry | Chabris, Christopher F. | Cherkas, Lynn | Chung, Mina K. | Cucca, Francesco | de Andrade, Mariza | De Jager, Philip L. | De Neve, Jan-Emmanuel | Deary, Ian J. | Dedoussis, George V. | Deloukas, Panos | Dimitriou, Maria | Eiriksdottir, Gudny | Elderson, Martin F. | Eriksson, Johan G. | Evans, David M. | Faul, Jessica D. | Ferrucci, Luigi | Garcia, Melissa E. | Grönberg, Henrik | Gudnason, Vilmundur | Hall, Per | Harris, Juliette M. | Harris, Tamara B. | Hastie, Nicholas D. | Heath, Andrew C. | Hernandez, Dena G. | Hoffmann, Wolfgang | Hofman, Adriaan | Holle, Rolf | Holliday, Elizabeth G. | Hottenga, Jouke-Jan | Iacono, William G. | Illig, Thomas | Järvelin, Marjo-Riitta | Kähönen, Mika | Kaprio, Jaakko | Kirkpatrick, Robert M. | Kowgier, Matthew | Latvala, Antti | Launer, Lenore J. | Lawlor, Debbie A. | Lehtimäki, Terho | Li, Jingmei | Lichtenstein, Paul | Lichtner, Peter | Liewald, David C. | Madden, Pamela A. | Magnusson, Patrik K. E. | Mäkinen, Tomi E. | Masala, Marco | McGue, Matt | Metspalu, Andres | Mielck, Andreas | Miller, Michael B. | Montgomery, Grant W. | Mukherjee, Sutapa | Nyholt, Dale R. | Oostra, Ben A. | Palmer, Lyle J. | Palotie, Aarno | Penninx, Brenda | Perola, Markus | Peyser, Patricia A. | Preisig, Martin | Räikkönen, Katri | Raitakari, Olli T. | Realo, Anu | Ring, Susan M. | Ripatti, Samuli | Rivadeneira, Fernando | Rudan, Igor | Rustichini, Aldo | Salomaa, Veikko | Sarin, Antti-Pekka | Schlessinger, David | Scott, Rodney J. | Snieder, Harold | Pourcain, Beate St | Starr, John M. | Sul, Jae Hoon | Surakka, Ida | Svento, Rauli | Teumer, Alexander | Tiemeier, Henning | Rooij, Frank JAan | Van Wagoner, David R. | Vartiainen, Erkki | Viikari, Jorma | Vollenweider, Peter | Vonk, Judith M. | Waeber, Gérard | Weir, David R. | Wichmann, H.-Erich | Widen, Elisabeth | Willemsen, Gonneke | Wilson, James F. | Wright, Alan F. | Conley, Dalton | Davey-Smith, George | Franke, Lude | Groenen, Patrick J. F. | Hofman, Albert | Johannesson, Magnus | Kardia, Sharon L.R. | Krueger, Robert F. | Laibson, David | Martin, Nicholas G. | Meyer, Michelle N. | Posthuma, Danielle | Thurik, A. Roy | Timpson, Nicholas J. | Uitterlinden, André G. | van Duijn, Cornelia M. | Visscher, Peter M. | Benjamin, Daniel J. | Cesarini, David | Koellinger, Philipp D.
Science (New York, N.Y.)  2013;340(6139):1467-1471.
A genome-wide association study of educational attainment was conducted in a discovery sample of 101,069 individuals and a replication sample of 25,490. Three independent SNPs are genome-wide significant (rs9320913, rs11584700, rs4851266), and all three replicate. Estimated effects sizes are small (R2 ≈ 0.02%), approximately 1 month of schooling per allele. A linear polygenic score from all measured SNPs accounts for ≈ 2% of the variance in both educational attainment and cognitive function. Genes in the region of the loci have previously been associated with health, cognitive, and central nervous system phenotypes, and bioinformatics analyses suggest the involvement of the anterior caudate nucleus. These findings provide promising candidate SNPs for follow-up work, and our effect size estimates can anchor power analyses in social-science genetics.
doi:10.1126/science.1235488
PMCID: PMC3751588  PMID: 23722424
23.  Parent-Offspring Body Mass Index Associations in the Norwegian Mother and Child Cohort Study: A Family-based Approach to Studying the Role of the Intrauterine Environment in Childhood Adiposity 
American Journal of Epidemiology  2012;176(2):83-92.
In the present study, the authors investigated the role of the intrauterine environment in childhood adiposity by comparing the maternal-offspring body mass index (BMI) association with the paternal-offspring BMI association when the offspring were 3 years of age, using parental prepregnancy BMI (measured as weight in kilograms divided by height in meters squared). The parent-offspring trios (n = 29,216) were recruited during pregnancy from 2001 to 2008 into the Norwegian Mother and Child Cohort Study conducted by The Norwegian Institute of Public Health. Data from self-administered questionnaires were used in linear regression analyses. Crude analyses showed similar parental-offspring BMI associations; the mean difference in offspring BMI was 0.15 (95% confidence interval: 0.13, 0.16) per each 1-standard-deviation increase in maternal BMI and 0.15 (95% confidence interval: 0.13, 0.17) per each 1-standard-deviation increase in paternal BMI. After all adjustments, the mean difference in offspring BMI per each 1-standard-deviation increment of maternal BMI was 0.12, and the mean difference in offspring BMI per each 1-standard-deviation increment of paternal BMI was 0.13. There was no strong support for heterogeneity between the associations (P > 0.6). In conclusion, results from the present large population-based study showed similar parental-offspring BMI associations when the offspring were 3 years of age, which indicates that the maternal-offspring association may be explained by shared familial (environmental and genetic) risk factors rather than by the intrauterine environment.
doi:10.1093/aje/kws134
PMCID: PMC3493198  PMID: 22771730
adiposity; body mass index; child, preschool; fathers; infant; mothers; overweight; pregnancy
24.  Associations of mortality with own height using son's height as an instrumental variable 
Economics and Human Biology  2013;11(3):351-359.
Highlights
► Associations of exposures with mortality may be confounded by existing ill health. ► We used a son's height as an instrument for parents’ height to avoid confounding. ► Parents of taller sons had lower cardiovascular and respiratory disease mortality. ► Parents of taller sons had higher mortality from cancer. ► Previous studies of height are not substantially confounded by existing ill health.
Height is associated with mortality from many diseases, but it remains unclear whether the association is causal or due to confounding by social factors, genetic pleiotropy,1 or existing ill-health. The authors investigated whether the association of height with mortality is causal by using a son's height as an instrumental variable (IV) for parents’ height among the parents of a cohort of 1,036,963 Swedish men born between 1951 and 1980 who had their height measured at military conscription, aged around 18, between 1969 and 2001. In a two-sample IV analysis adjusting for son's age at examination and secular trends in height, as well as parental age, and socioeconomic position, the hazard ratio (HR) for all-cause paternal mortality per standard deviation (SD, 6.49 cm) of height was 0.96 (95% confidence interval (CI): 0.95, 0.96). The results of IV analyses of mortality from all causes, cardiovascular disease (CVD), respiratory disease, cancer, external causes and suicide were comparable to those obtained using son's height as a simple proxy for own height and to conventional analyses of own height in the present data and elsewhere, suggesting that such conventional analyses are not substantially confounded by existing ill-health.
doi:10.1016/j.ehb.2012.04.003
PMCID: PMC3685807  PMID: 22560304
IV, instrumental variable; HR, hazard ratio; SD, standard deviation; CI, confidence interval; CVD, cardiovascular disease; BMI, body mass index; SEP, socioeconomic position; CHD, coronary heart disease; Body height; Mortality; Confounding factor; Causality; Cohort studies
25.  The Role of Adiposity in Cardiometabolic Traits: A Mendelian Randomization Analysis 
Fall, Tove | Hägg, Sara | Mägi, Reedik | Ploner, Alexander | Fischer, Krista | Horikoshi, Momoko | Sarin, Antti-Pekka | Thorleifsson, Gudmar | Ladenvall, Claes | Kals, Mart | Kuningas, Maris | Draisma, Harmen H. M. | Ried, Janina S. | van Zuydam, Natalie R. | Huikari, Ville | Mangino, Massimo | Sonestedt, Emily | Benyamin, Beben | Nelson, Christopher P. | Rivera, Natalia V. | Kristiansson, Kati | Shen, Huei-yi | Havulinna, Aki S. | Dehghan, Abbas | Donnelly, Louise A. | Kaakinen, Marika | Nuotio, Marja-Liisa | Robertson, Neil | de Bruijn, Renée F. A. G. | Ikram, M. Arfan | Amin, Najaf | Balmforth, Anthony J. | Braund, Peter S. | Doney, Alexander S. F. | Döring, Angela | Elliott, Paul | Esko, Tõnu | Franco, Oscar H. | Gretarsdottir, Solveig | Hartikainen, Anna-Liisa | Heikkilä, Kauko | Herzig, Karl-Heinz | Holm, Hilma | Hottenga, Jouke Jan | Hyppönen, Elina | Illig, Thomas | Isaacs, Aaron | Isomaa, Bo | Karssen, Lennart C. | Kettunen, Johannes | Koenig, Wolfgang | Kuulasmaa, Kari | Laatikainen, Tiina | Laitinen, Jaana | Lindgren, Cecilia | Lyssenko, Valeriya | Läärä, Esa | Rayner, Nigel W. | Männistö, Satu | Pouta, Anneli | Rathmann, Wolfgang | Rivadeneira, Fernando | Ruokonen, Aimo | Savolainen, Markku J. | Sijbrands, Eric J. G. | Small, Kerrin S. | Smit, Jan H. | Steinthorsdottir, Valgerdur | Syvänen, Ann-Christine | Taanila, Anja | Tobin, Martin D. | Uitterlinden, Andre G. | Willems, Sara M. | Willemsen, Gonneke | Witteman, Jacqueline | Perola, Markus | Evans, Alun | Ferrières, Jean | Virtamo, Jarmo | Kee, Frank | Tregouet, David-Alexandre | Arveiler, Dominique | Amouyel, Philippe | Ferrario, Marco M. | Brambilla, Paolo | Hall, Alistair S. | Heath, Andrew C. | Madden, Pamela A. F. | Martin, Nicholas G. | Montgomery, Grant W. | Whitfield, John B. | Jula, Antti | Knekt, Paul | Oostra, Ben | van Duijn, Cornelia M. | Penninx, Brenda W. J. H. | Davey Smith, George | Kaprio, Jaakko | Samani, Nilesh J. | Gieger, Christian | Peters, Annette | Wichmann, H.-Erich | Boomsma, Dorret I. | de Geus, Eco J. C. | Tuomi, TiinaMaija | Power, Chris | Hammond, Christopher J. | Spector, Tim D. | Lind, Lars | Orho-Melander, Marju | Palmer, Colin Neil Alexander | Morris, Andrew D. | Groop, Leif | Järvelin, Marjo-Riitta | Salomaa, Veikko | Vartiainen, Erkki | Hofman, Albert | Ripatti, Samuli | Metspalu, Andres | Thorsteinsdottir, Unnur | Stefansson, Kari | Pedersen, Nancy L. | McCarthy, Mark I. | Ingelsson, Erik | Prokopenko, Inga
PLoS Medicine  2013;10(6):e1001474.
In this study, Prokopenko and colleagues provide novel evidence for causal relationship between adiposity and heart failure and increased liver enzymes using a Mendelian randomization study design.
Please see later in the article for the Editors' Summary
Background
The association between adiposity and cardiometabolic traits is well known from epidemiological studies. Whilst the causal relationship is clear for some of these traits, for others it is not. We aimed to determine whether adiposity is causally related to various cardiometabolic traits using the Mendelian randomization approach.
Methods and Findings
We used the adiposity-associated variant rs9939609 at the FTO locus as an instrumental variable (IV) for body mass index (BMI) in a Mendelian randomization design. Thirty-six population-based studies of individuals of European descent contributed to the analyses.
Age- and sex-adjusted regression models were fitted to test for association between (i) rs9939609 and BMI (n = 198,502), (ii) rs9939609 and 24 traits, and (iii) BMI and 24 traits. The causal effect of BMI on the outcome measures was quantified by IV estimators. The estimators were compared to the BMI–trait associations derived from the same individuals. In the IV analysis, we demonstrated novel evidence for a causal relationship between adiposity and incident heart failure (hazard ratio, 1.19 per BMI-unit increase; 95% CI, 1.03–1.39) and replicated earlier reports of a causal association with type 2 diabetes, metabolic syndrome, dyslipidemia, and hypertension (odds ratio for IV estimator, 1.1–1.4; all p<0.05). For quantitative traits, our results provide novel evidence for a causal effect of adiposity on the liver enzymes alanine aminotransferase and gamma-glutamyl transferase and confirm previous reports of a causal effect of adiposity on systolic and diastolic blood pressure, fasting insulin, 2-h post-load glucose from the oral glucose tolerance test, C-reactive protein, triglycerides, and high-density lipoprotein cholesterol levels (all p<0.05). The estimated causal effects were in agreement with traditional observational measures in all instances except for type 2 diabetes, where the causal estimate was larger than the observational estimate (p = 0.001).
Conclusions
We provide novel evidence for a causal relationship between adiposity and heart failure as well as between adiposity and increased liver enzymes.
Please see later in the article for the Editors' Summary
Editors' Summary
Cardiovascular disease (CVD)—disease that affects the heart and/or the blood vessels—is a major cause of illness and death worldwide. In the US, for example, coronary heart disease—a CVD in which narrowing of the heart's blood vessels by fatty deposits slows the blood supply to the heart and may eventually cause a heart attack—is the leading cause of death, and stroke—a CVD in which the brain's blood supply is interrupted—is the fourth leading cause of death. Globally, both the incidence of CVD (the number of new cases in a population every year) and its prevalence (the proportion of the population with CVD) are increasing, particularly in low- and middle-income countries. This increasing burden of CVD is occurring in parallel with a global increase in the incidence and prevalence of obesity—having an unhealthy amount of body fat (adiposity)—and of metabolic diseases—conditions such as diabetes in which metabolism (the processes that the body uses to make energy from food) is disrupted, with resulting high blood sugar and damage to the blood vessels.
Why Was This Study Done?
Epidemiological studies—investigations that record the patterns and causes of disease in populations—have reported an association between adiposity (indicated by an increased body mass index [BMI], which is calculated by dividing body weight in kilograms by height in meters squared) and cardiometabolic traits such as coronary heart disease, stroke, heart failure (a condition in which the heart is incapable of pumping sufficient amounts of blood around the body), diabetes, high blood pressure (hypertension), and high blood cholesterol (dyslipidemia). However, observational studies cannot prove that adiposity causes any particular cardiometabolic trait because overweight individuals may share other characteristics (confounding factors) that are the real causes of both obesity and the cardiometabolic disease. Moreover, it is possible that having CVD or a metabolic disease causes obesity (reverse causation). For example, individuals with heart failure cannot do much exercise, so heart failure may cause obesity rather than vice versa. Here, the researchers use “Mendelian randomization” to examine whether adiposity is causally related to various cardiometabolic traits. Because gene variants are inherited randomly, they are not prone to confounding and are free from reverse causation. It is known that a genetic variant (rs9939609) within the genome region that encodes the fat-mass- and obesity-associated gene (FTO) is associated with increased BMI. Thus, an investigation of the associations between rs9939609 and cardiometabolic traits can indicate whether obesity is causally related to these traits.
What Did the Researchers Do and Find?
The researchers analyzed the association between rs9939609 (the “instrumental variable,” or IV) and BMI, between rs9939609 and 24 cardiometabolic traits, and between BMI and the same traits using genetic and health data collected in 36 population-based studies of nearly 200,000 individuals of European descent. They then quantified the strength of the causal association between BMI and the cardiometabolic traits by calculating “IV estimators.” Higher BMI showed a causal relationship with heart failure, metabolic syndrome (a combination of medical disorders that increases the risk of developing CVD), type 2 diabetes, dyslipidemia, hypertension, increased blood levels of liver enzymes (an indicator of liver damage; some metabolic disorders involve liver damage), and several other cardiometabolic traits. All the IV estimators were similar to the BMI–cardiovascular trait associations (observational estimates) derived from the same individuals, with the exception of diabetes, where the causal estimate was higher than the observational estimate, probably because the observational estimate is based on a single BMI measurement, whereas the causal estimate considers lifetime changes in BMI.
What Do These Findings Mean?
Like all Mendelian randomization studies, the reliability of the causal associations reported here depends on several assumptions made by the researchers. Nevertheless, these findings provide support for many previously suspected and biologically plausible causal relationships, such as that between adiposity and hypertension. They also provide new insights into the causal effect of obesity on liver enzyme levels and on heart failure. In the latter case, these findings suggest that a one-unit increase in BMI might increase the incidence of heart failure by 17%. In the US, this corresponds to 113,000 additional cases of heart failure for every unit increase in BMI at the population level. Although additional studies are needed to confirm and extend these findings, these results suggest that global efforts to reduce the burden of obesity will likely also reduce the occurrence of CVD and metabolic disorders.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001474.
The American Heart Association provides information on all aspects of cardiovascular disease and tips on keeping the heart healthy, including weight management (in several languages); its website includes personal stories about stroke and heart attacks
The US Centers for Disease Control and Prevention has information on heart disease, stroke, and all aspects of overweight and obesity (in English and Spanish)
The UK National Health Service Choices website provides information about cardiovascular disease and obesity, including a personal story about losing weight
The World Health Organization provides information on obesity (in several languages)
The International Obesity Taskforce provides information about the global obesity epidemic
Wikipedia has a page on Mendelian randomization (note: Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
MedlinePlus provides links to other sources of information on heart disease, on vascular disease, on obesity, and on metabolic disorders (in English and Spanish)
The International Association for the Study of Obesity provides maps and information about obesity worldwide
The International Diabetes Federation has a web page that describes types, complications, and risk factors of diabetes
doi:10.1371/journal.pmed.1001474
PMCID: PMC3692470  PMID: 23824655

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