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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.  Stratification by Smoking Status Reveals an Association of CHRNA5-A3-B4 Genotype with Body Mass Index in Never Smokers 
PLoS Genetics  2014;10(12):e1004799.
We previously used a single nucleotide polymorphism (SNP) in the CHRNA5-A3-B4 gene cluster associated with heaviness of smoking within smokers to confirm the causal effect of smoking in reducing body mass index (BMI) in a Mendelian randomisation analysis. While seeking to extend these findings in a larger sample we found that this SNP is associated with 0.74% lower body mass index (BMI) per minor allele in current smokers (95% CI -0.97 to -0.51, P = 2.00×10−10), but also unexpectedly found that it was associated with 0.35% higher BMI in never smokers (95% CI +0.18 to +0.52, P = 6.38×10−5). An interaction test confirmed that these estimates differed from each other (P = 4.95×10−13). This difference in effects suggests the variant influences BMI both via pathways unrelated to smoking, and via the weight-reducing effects of smoking. It would therefore be essentially undetectable in an unstratified genome-wide association study of BMI, given the opposite association with BMI in never and current smokers. This demonstrates that novel associations may be obscured by hidden population sub-structure. Stratification on well-characterized environmental factors known to impact on health outcomes may therefore reveal novel genetic associations.
Author Summary
We found that a single nucleotide polymorphism in the CHRNA5-A3-B4 gene cluster, which is known to influence smoking heaviness, is associated with lower body mass index (BMI) in current smokers, but higher BMI in never smokers. This difference in effects suggests that the variant influences BMI both via pathways other than smoking, and via the weight-reducing effects of smoking, in opposite directions. The overall effect on BMI would therefore be undetectable in an unstratified genome-wide association study, indicating that novel associations may be obscured by hidden population sub-structure.
doi:10.1371/journal.pgen.1004799
PMCID: PMC4256159  PMID: 25474695
3.  Prepubertal start of father's smoking and increased body fat in his sons: further characterisation of paternal transgenerational responses 
European Journal of Human Genetics  2014;22(12):1382-1386.
Despite interest in the idea that transgenerational effects of adverse exposures might contribute to population health trends, there are few human data. This non-genetic inheritance is all the more remarkable when transmission is down the male-line as reported in a historical Swedish study, where the paternal grandfather's food supply in mid childhood was associated with the mortality rate in his grandsons. Using the Avon Longitudinal Study of Parents and Children's questionnaire data on smoking and smoking onset from 9886 fathers, we examined the growth of their children from 7–17 years. Adjusting for potential confounders, we assessed associations between body mass index (BMI), waist circumference, total fat mass and lean mass with the age at which the father had started smoking regularly. Of 5376 fathers who reported having ever smoked, 166 reported regular smoking <11 years of age. Before adjustment, those offspring whose fathers started smoking <11 years had the highest mean BMIs at each age tested. The adjusted mean differences in BMI, waist circumference and total fat mass in those sons whose fathers started smoking <11 years, compared with all other sons, increased with age, being significantly greater from 13 years onwards. There were no significant BMI associations in daughters, but they showed a reduction in total lean mass. Our results highlight the importance of the developmental timing of the paternal exposure as well as gender differences in offspring outcomes. Smoking by boys in mid childhood may contribute to obesity in adolescent boys of the next generation.
doi:10.1038/ejhg.2014.31
PMCID: PMC4085023  PMID: 24690679
4.  Haptoglobin Duplicon, Hemoglobin, and Vitamin C: Analyses in the British Women's Heart and Health Study and Caerphilly Prospective Study 
Disease Markers  2014;2014:529456.
Background. Haptoglobin acts as an antioxidant by limiting peroxidative tissue damage by free hemoglobin. The haptoglobin gene allele Hp2 comprises a 1.7 kb partial duplication. Relative to allele Hp1, Hp2 carriers form protein multimers, suboptimal for hemoglobin scavenging. Objective. To examine the association of haptoglobin genotype with a range of phenotypes, with emphasis on vitamin C and hemoglobin levels. Methods. We applied a quantitative PCR assay for the duplication junction to two population cohorts including 2747 British women and 1198 British men. We examined the association of haptoglobin duplicon copy number with hemoglobin and vitamin C and used the copy number to complete a phenome scan. Results. Hemoglobin concentrations were greater in those with Hp2,2 genotype, in women only (Hp1,1 13.45 g/dL, Hp1,2 13.49 g/dL, Hp2,2 13.61 g/dL; P = 0.002), though statistically there was no evidence of a difference between the sexes (z value = 1.2, P = 0.24). Haptoglobin genotype was not associated with vitamin C or any other phenotype in either cohort. Conclusions. Our results do not support association of haptoglobin genotype with vitamin C or with other phenotypes measured in two population cohorts. The apparent association between haptoglobin genotype and hemoglobin in the women's cohort merits further investigation.
doi:10.1155/2014/529456
PMCID: PMC4265517  PMID: 25525287
5.  Variation in the SLC23A1 gene does not influence cardiometabolic outcomes to the extent expected given its association with l-ascorbic acid1234 
Background: Observational studies showed that circulating l-ascorbic acid (vitamin C) is inversely associated with cardiometabolic traits. However, these studies were susceptible to confounding and reverse causation.
Objectives: We assessed the relation between l-ascorbic acid and 10 cardiometabolic traits by using a single nucleotide polymorphism in the solute carrier family 23 member 1 (SLC23A1) gene (rs33972313) associated with circulating l-ascorbic acid concentrations. The observed association between rs33972313 and cardiometabolic outcomes was compared with that expected given the rs33972313-l-ascorbic acid and l-ascorbic acid–outcome associations.
Design: A meta-analysis was performed in the following 5 independent studies: the British Women's Heart and Health Study (n = 1833), the MIDSPAN study (n = 1138), the Ten Towns study (n = 1324), the British Regional Heart Study (n = 2521), and the European Prospective Investigation into Cancer (n = 3737).
Results: With the use of a meta-analysis of observational estimates, inverse associations were shown between l-ascorbic acid and systolic blood pressure, triglycerides, and the waist-hip ratio [the strongest of which was the waist-hip ratio (−0.13-SD change; 95% CI: −0.20-, −0.07-SD change; P = 0.0001) per SD increase in l-ascorbic acid], and a positive association was shown with high-density lipoprotein (HDL) cholesterol. The variation at rs33972313 was associated with a 0.18-SD (95% CI: 0.10-, 0.25-SD; P = 3.34 × 10−6) increase in l-ascorbic acid per effect allele. There was no evidence of a relation between the variation at rs33972313 and any cardiometabolic outcome. Although observed estimates were not statistically different from expected associations between rs33972313 and cardiometabolic outcomes, estimates for low-density lipoprotein cholesterol, HDL cholesterol, triglycerides, glucose, and body mass index were in the opposite direction to those expected.
Conclusions: The nature of the genetic association exploited in this study led to limited statistical application, but despite this, when all cardiometabolic traits were assessed, there was no evidence of any trend supporting a protective role of l-ascorbic acid. In the context of existing work, these results add to the suggestion that observational relations between l-ascorbic acid and cardiometabolic health may be attributable to confounding and reverse causation.
doi:10.3945/ajcn.114.092981
PMCID: PMC4266888  PMID: 25527764
l-ascorbic acid; cardiometabolic traits; confounding; genetic variants; reverse causation
6.  Analysis of Self-Selection Bias in a Population-Based Cohort Study of Autism Spectrum Disorders 
Paediatric and perinatal epidemiology  2013;27(6):10.1111/ppe.12077.
Background
This study examined potential self-selection bias in a large pregnancy cohort by comparing exposure-outcome associations from the cohort to similar associations obtained from nationwide registry data. The outcome under study was specialist-confirmed diagnosis of autism spectrum disorders.
Methods
The cohort sample (n = 89,836) was derived from the population-based prospective Norwegian Mother and Child Cohort Study and its sub-study of autism spectrum disorders, the Autism Birth Cohort study. The nationwide registry data were derived from the Medical Birth Registry of Norway (n = 507,856). The children were born in 1999-2007, and seven prenatal and perinatal exposures were selected for analyses.
Results
Autism spectrum disorders were reported for 234 (0.26%) children in the cohort and 2,072 (0.41%) in the nationwide population. Compared with the nationwide population, the cohort had an underrepresentation of the youngest women (<25 years), those who had single status, mothers who smoked during pregnancy, and nonusers of prenatal folic acid supplements. The ratios of the adjusted odds ratios in the cohort over the adjusted odds ratios in the nationwide population were as follows; primipara pregnancy: 1.39/1.22, prenatal folic acid use: 0.85/0.86, prenatal smoking: 1.20/1.17, preterm birth (<37 weeks): 1.48/1.42, low birthweight (<2,500 g): 1.60/1.58, male sex: 4.39/4.59 (unadjusted only); and cesarean section history: 1.03/1.04.
Conclusions
Associations estimated between autism spectrum disorders and perinatal and prenatal exposures in the cohort are close to those estimated in the nationwide population. Self-selection does not appear to compromise validity of exposure-outcome associations in the Autism Birth Cohort study.
doi:10.1111/ppe.12077
PMCID: PMC3851582  PMID: 23919580
7.  Associations Between Change in Sleep Duration and Inflammation: Findings on C-reactive Protein and Interleukin 6 in the Whitehall II Study 
American Journal of Epidemiology  2013;178(6):956-961.
Cross-sectional evidence suggests associations between sleep duration and levels of the inflammatory markers, C-reactive protein and interleukin-6. This longitudinal study uses data from the London-based Whitehall II study to examine whether changes in sleep duration are associated with average levels of inflammation from 2 measures 5 years apart. Sleep duration (≤5, 6, 7, 8, ≥9 hours on an average week night) was assessed in 5,003 middle-aged women and men in 1991/1994 and 1997/1999. Fasting levels of C-reactive protein and interleukin-6 were measured in 1997/1999 and 2002/2004. Cross-sectional analyses indicated that shorter sleep is associated with higher levels of inflammatory markers. Longitudinal analyses showed that each hour per night decrease in sleep duration between 1991/1994 and 1997/1999 was associated with higher levels of C-reactive protein (8.1%) and interleukin-6 (4.5%) averaged across measures in 1997/1999 and 2002/2004. Adjustment for longstanding illness and major cardiometabolic risk factors indicated that disease processes may partially underlie these associations. An increase in sleep duration was not associated with average levels of inflammatory markers. These results suggest that both short sleep and reductions in sleep are associated with average levels of inflammation over a 5-year period.
doi:10.1093/aje/kwt072
PMCID: PMC3817449  PMID: 23801012
change in sleep duration; C-reactive protein; inflammatory markers; interleukin-6; sleep duration
8.  Prenatal exposure to binge pattern of alcohol consumption: mental health and learning outcomes at age 11 
The objective of the study is to investigate whether episodic binge pattern of alcohol consumption during pregnancy is independently associated with child mental health and academic outcomes. Using data from the prospective, population-based Avon Longitudinal Study of Parents and Children (ALSPAC), we investigated the associations between binge patterns of alcohol consumption during pregnancy (≥4 drinks per day) and child mental health [as rated by both parent (n = 4,610) and teacher (n = 4,274)] and academic outcomes [based on examination results (n = 6,939)] at age 11 years. After adjusting for prenatal and postnatal risk factors, binge pattern of alcohol consumption (≥4 drinks in a day on at least one occasion) during pregnancy was associated with higher levels of mental health problems (especially hyperactivity/inattention) in girls at age 11 years, according to parental report. After disentangling binge-pattern and daily drinking, binge-pattern drinking was independently associated with teacher-rated hyperactivity/inattention and lower academic scores in both genders. Episodic drinking involving ≥4 drinks per day during pregnancy may increase risk for child mental health problems and lower academic attainment even if daily average levels of alcohol consumption are low. Episodic binge pattern of drinking appears to be a risk factor for these outcomes, especially hyperactivity and inattention problems, in the absence of daily drinking.
Electronic supplementary material
The online version of this article (doi:10.1007/s00787-014-0599-7) contains supplementary material, which is available to authorized users.
doi:10.1007/s00787-014-0599-7
PMCID: PMC4186965  PMID: 25209690
Prenatal alcohol exposure; Fetal alcohol spectrum disorder; Academic achievement; Mental health problems; Hyperactivity
9.  Perinatal depression and omega-3 fatty acids: A Mendelian randomisation study 
Journal of Affective Disorders  2014;166(100):124-131.
Background
There have been numerous studies investigating the association between omega-3 fatty acids (FAs) and depression, with mixed findings. We propose an approach which is largely free from issues such as confounding or reverse causality, to investigate this relationship using observational data from a pregnancy cohort.
Methods
The Avon Longitudinal Study of Parents and Children (ALSPAC) cohort collected information on FA levels from antenatal blood samples and depressive symptoms at several time points during pregnancy and the postnatal period. Conventional epidemiological analyses were used in addition to a Mendelian randomisation (MR) approach to investigate the association between levels of two omega-3 FAs (docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)) and perinatal onset depression, antenatal depression (AND) and postnatal depression (PND).
Results
Weak evidence of a positive association with both EPA (OR=1.07; 95% CI: 0.99–1.15) and DHA (OR=1.08; 95% CI: 0.98–1.19) with perinatal onset depression was found using a multivariable logistic regression adjusting for social class and maternal age. However, the strength of association was found to attenuate when using an MR analysis to investigate DHA.
Limitations
Pleiotropy is a potential limitation in MR analyses; we assume that the genetic variants included in the instrumental variable are associated only with our trait of interest (FAs) and thus cannot influence the outcome via any other pathway.
Conclusions
We found weak evidence of a positive association between omega-3 FAs and perinatal onset depression. However, without confirmation from the MR analysis, we are unable to draw conclusions regarding causality.
doi:10.1016/j.jad.2014.04.077
PMCID: PMC4101243  PMID: 25012420
Depression; Perinatal; Mendelian randomisation; Omega-3; ALSPAC
10.  Can a genotype for lactase persistence be used as a tool to assess the relationship between renal cell carcinoma and milk drinking? Pitfalls in the application of Mendelian randomization 
Background
Increased risk of renal cell carcinoma (RCC) with milk consumption has been reported from observational studies including that involved here. Whether this represents causal association or whether it is the result of confounding or bias is unclear. We aimed to assess the potential for genetic variation in lactase persistence to be used as a tool for the interrogation of these relationships.
Methods
Using a large, hospital based case control study, we use a combination of observational genetic and phenotypic data to determine whether the MCM6 -13910 C/T(rs4988235) variant may be used as an non-confounded and unbiased marker for milk consumption.
Results
Consumption of milk during adulthood was associated with increased risk of RCC (OR=1.35 95% CI 1.03, 1.76 p=0.03). Among controls, consumption of milk was associated with the lactase persistence genotype at rs4988235 (2.39[1.81, 3.15], p=6.9*10−10), however the same genotype was not associated with RCC (OR=1.01 95% CI 0.83, 1.22 p=0.9). In controls, milk consumption was associated with confounding factors including smoking, and educational attainment, while the lactase persistence genotype at rs4988235 genotype showed negligible association with confounding factors.
Conclusions
The absence of an association between the MCM6 genotype and RCC suggests that observational associations between milk consumption and RCC may be due to confounding or bias. However, if the association between genotype and behavioral exposure is weak, then the power of this test may be low. The nature of intermediate risk factor instrumentation is an important consideration in the undertaking and interpretation of this type of causal analysis experiment.
doi:10.1158/1055-9965.EPI-09-1019
PMCID: PMC4141143  PMID: 20447925
Mendelian randomization; lactase persistence; renal carcinoma
11.  Differences between blood donors and a population sample: implications for case–control studies 
Background Selecting appropriate controls for studies of genetic variation in case series is important. The two major candidates involve the use of blood donors or a random sample of the population.
Methods We compare and contrast the two different populations of controls for studies of genetic variation using data from parents enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC). In addition we compute different biases using a series of hypothetical assumptions.
Results The study subjects who had been blood donors differed markedly from the general population in social, health-related, anthropometric, and personality-related variables. Using theoretical examples, we show that blood donors are a poor control group for non-genetic studies of diseases related to environmentally, behaviourally, or socially patterned exposures. However, we show that if blood donors are used as controls in genetic studies, these factors are unlikely to make a major difference in detecting true associations with relatively rare disorders (cumulative incidence through life of <10%). Nevertheless, for more common disorders, the reduction in accuracy resulting from the inclusion in any control population of individuals who have or will develop the disease in question can create a greater bias than can socially patterned factors.
Conclusions Information about the medical history of a control and the parents of the control (as a proxy for whether the control will develop the disease) is more important with regard to the choice of controls than whether the controls are a random population sample or blood donors.
doi:10.1093/ije/dyt095
PMCID: PMC3781001  PMID: 23825379
ALSPAC; blood donors; genetic studies; case-control studies; methodology
12.  Phenotype Refinement Strengthens the Association of AHR and CYP1A1 Genotype with Caffeine Consumption 
PLoS ONE  2014;9(7):e103448.
Two genetic loci, one in the cytochrome P450 1A1 (CYP1A1) and 1A2 (CYP1A2) gene region (rs2472297) and one near the aryl-hydrocarbon receptor (AHR) gene (rs6968865), have been associated with habitual caffeine consumption. We sought to establish whether a more refined and comprehensive assessment of caffeine consumption would provide stronger evidence of association, and whether a combined allelic score comprising these two variants would further strengthen the association. We used data from between 4,460 and 7,520 women in the Avon Longitudinal Study of Parents and Children, a longitudinal birth cohort based in the United Kingdom. Self-report data on coffee, tea and cola consumption (including consumption of decaffeinated drinks) were available at multiple time points. Both genotypes were individually associated with total caffeine consumption, and with coffee and tea consumption. There was no association with cola consumption, possibly due to low levels of consumption in this sample. There was also no association with measures of decaffeinated drink consumption, indicating that the observed association is most likely mediated via caffeine. The association was strengthened when a combined allelic score was used, accounting for up to 1.28% of phenotypic variance. This was not associated with potential confounders of observational association. A combined allelic score accounts for sufficient phenotypic variance in caffeine consumption that this may be useful in Mendelian randomization studies. Future studies may therefore be able to use this combined allelic score to explore causal effects of habitual caffeine consumption on health outcomes.
doi:10.1371/journal.pone.0103448
PMCID: PMC4116211  PMID: 25075865
13.  Cis and Trans Effects of Human Genomic Variants on Gene Expression 
PLoS Genetics  2014;10(7):e1004461.
Gene expression is a heritable cellular phenotype that defines the function of a cell and can lead to diseases in case of misregulation. In order to detect genetic variations affecting gene expression, we performed association analysis of single nucleotide polymorphisms (SNPs) and copy number variants (CNVs) with gene expression measured in 869 lymphoblastoid cell lines of the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort in cis and in trans. We discovered that 3,534 genes (false discovery rate (FDR) = 5%) are affected by an expression quantitative trait locus (eQTL) in cis and 48 genes are affected in trans. We observed that CNVs are more likely to be eQTLs than SNPs. In addition, we found that variants associated to complex traits and diseases are enriched for trans-eQTLs and that trans-eQTLs are enriched for cis-eQTLs. As a variant affecting both a gene in cis and in trans suggests that the cis gene is functionally linked to the trans gene expression, we looked specifically for trans effects of cis-eQTLs. We discovered that 26 cis-eQTLs are associated to 92 genes in trans with the cis-eQTLs of the transcriptions factors BATF3 and HMX2 affecting the most genes. We then explored if the variation of the level of expression of the cis genes were causally affecting the level of expression of the trans genes and discovered several causal relationships between variation in the level of expression of the cis gene and variation of the level of expression of the trans gene. This analysis shows that a large sample size allows the discovery of secondary effects of human variations on gene expression that can be used to construct short directed gene regulatory networks.
Author Summary
Humans differ in their genetic sequences at millions of positions but only a subset of these differences have a functional effect. In order to detect functional genetic differences, we assessed the impact of common genetic variants on gene expression in 869 individuals and discovered that the expression of many genes is affected by common variants in cis or in trans. We show that the effect of some variants on gene expression cannot be detected in other tissues, highlighting the tissue specificity of gene regulation. In addition, we show that variants associated to common diseases are more likely to affect gene expression in cis and in trans. Finally, we show that variants affecting gene expression in cis often affect gene expression in trans, which suggests that the trans effects are due to the cis genes expression. We tested this hypothesis and discovered several cases of genes regulated in trans by a cis regulated gene in a causal manner. This shows that a population-based strategy with a large number of individuals has the potential to detect secondary effects of common variants that can be used to construct short directed regulatory networks.
doi:10.1371/journal.pgen.1004461
PMCID: PMC4091791  PMID: 25010687
14.  Genome Wide Association Identifies Common Variants at the SERPINA6/SERPINA1 Locus Influencing Plasma Cortisol and Corticosteroid Binding Globulin 
PLoS Genetics  2014;10(7):e1004474.
Variation in plasma levels of cortisol, an essential hormone in the stress response, is associated in population-based studies with cardio-metabolic, inflammatory and neuro-cognitive traits and diseases. Heritability of plasma cortisol is estimated at 30–60% but no common genetic contribution has been identified. The CORtisol NETwork (CORNET) consortium undertook genome wide association meta-analysis for plasma cortisol in 12,597 Caucasian participants, replicated in 2,795 participants. The results indicate that <1% of variance in plasma cortisol is accounted for by genetic variation in a single region of chromosome 14. This locus spans SERPINA6, encoding corticosteroid binding globulin (CBG, the major cortisol-binding protein in plasma), and SERPINA1, encoding α1-antitrypsin (which inhibits cleavage of the reactive centre loop that releases cortisol from CBG). Three partially independent signals were identified within the region, represented by common SNPs; detailed biochemical investigation in a nested sub-cohort showed all these SNPs were associated with variation in total cortisol binding activity in plasma, but some variants influenced total CBG concentrations while the top hit (rs12589136) influenced the immunoreactivity of the reactive centre loop of CBG. Exome chip and 1000 Genomes imputation analysis of this locus in the CROATIA-Korcula cohort identified missense mutations in SERPINA6 and SERPINA1 that did not account for the effects of common variants. These findings reveal a novel common genetic source of variation in binding of cortisol by CBG, and reinforce the key role of CBG in determining plasma cortisol levels. In turn this genetic variation may contribute to cortisol-associated degenerative diseases.
Author Summary
Cortisol is a steroid hormone from the adrenal glands that is essential in the response to stress. Most cortisol in blood is bound to corticosteroid binding globulin (CBG). Diseases causing cortisol deficiency (Addison's disease) or excess (Cushing's syndrome) are life-threatening. Variations in plasma cortisol have been associated with cardiovascular and psychiatric diseases and their risk factors. To dissect the genetic contribution to variation in plasma cortisol, we formed the CORtisol NETwork (CORNET) consortium and recruited collaborators with suitable samples from more than 15,000 people. The results reveal that the major genetic influence on plasma cortisol is mediated by variations in the binding capacity of CBG. This is determined by differences in the circulating concentrations of CBG and also in the immunoreactivity of its ‘reactive centre loop’, potentially influencing not only binding affinity for cortisol but also the stability of CBG and hence the tissue delivery of cortisol. These findings provide the first evidence for a common genetic effect on levels of this clinically important hormone, suggest that differences in CBG between individuals are biologically important, and pave the way for further research to dissect causality in the associations of plasma cortisol with common diseases.
doi:10.1371/journal.pgen.1004474
PMCID: PMC4091794  PMID: 25010111
15.  Mendelian randomization: genetic anchors for causal inference in epidemiological studies 
Human Molecular Genetics  2014;23(R1):R89-R98.
Observational epidemiological studies are prone to confounding, reverse causation and various biases and have generated findings that have proved to be unreliable indicators of the causal effects of modifiable exposures on disease outcomes. Mendelian randomization (MR) is a method that utilizes genetic variants that are robustly associated with such modifiable exposures to generate more reliable evidence regarding which interventions should produce health benefits. The approach is being widely applied, and various ways to strengthen inference given the known potential limitations of MR are now available. Developments of MR, including two-sample MR, bidirectional MR, network MR, two-step MR, factorial MR and multiphenotype MR, are outlined in this review. The integration of genetic information into population-based epidemiological studies presents translational opportunities, which capitalize on the investment in genomic discovery research.
doi:10.1093/hmg/ddu328
PMCID: PMC4170722  PMID: 25064373
16.  Phenotypic Dissection of Bone Mineral Density Reveals Skeletal Site Specificity and Facilitates the Identification of Novel Loci in the Genetic Regulation of Bone Mass Attainment 
PLoS Genetics  2014;10(6):e1004423.
Heritability of bone mineral density (BMD) varies across skeletal sites, reflecting different relative contributions of genetic and environmental influences. To quantify the degree to which common genetic variants tag and environmental factors influence BMD, at different sites, we estimated the genetic (rg) and residual (re) correlations between BMD measured at the upper limbs (UL-BMD), lower limbs (LL-BMD) and skull (SK-BMD), using total-body DXA scans of ∼4,890 participants recruited by the Avon Longitudinal Study of Parents and their Children (ALSPAC). Point estimates of rg indicated that appendicular sites have a greater proportion of shared genetic architecture (LL-/UL-BMD rg = 0.78) between them, than with the skull (UL-/SK-BMD rg = 0.58 and LL-/SK-BMD rg = 0.43). Likewise, the residual correlation between BMD at appendicular sites (re = 0.55) was higher than the residual correlation between SK-BMD and BMD at appendicular sites (re = 0.20–0.24). To explore the basis for the observed differences in rg and re, genome-wide association meta-analyses were performed (n∼9,395), combining data from ALSPAC and the Generation R Study identifying 15 independent signals from 13 loci associated at genome-wide significant level across different skeletal regions. Results suggested that previously identified BMD-associated variants may exert site-specific effects (i.e. differ in the strength of their association and magnitude of effect across different skeletal sites). In particular, variants at CPED1 exerted a larger influence on SK-BMD and UL-BMD when compared to LL-BMD (P = 2.01×10−37), whilst variants at WNT16 influenced UL-BMD to a greater degree when compared to SK- and LL-BMD (P = 2.31×10−14). In addition, we report a novel association between RIN3 (previously associated with Paget's disease) and LL-BMD (rs754388: β = 0.13, SE = 0.02, P = 1.4×10−10). Our results suggest that BMD at different skeletal sites is under a mixture of shared and specific genetic and environmental influences. Allowing for these differences by performing genome-wide association at different skeletal sites may help uncover new genetic influences on BMD.
Author Summary
The heritability of bone mineral density (BMD) varies across skeletal sites, reflecting different relative contributions of genetic and environmental influences. To investigate whether the genes underlying bone acquisition act in a site-specific manner, we quantified the shared genetic influences across axial and appendicular skeletal sites by estimating the genetic and residual correlation of BMD at the upper limb, lower limb and the skull. Our results suggest that different skeletal sites as measured by total-body Dual-Energy X-Ray Absorptiometry are to a certain extent under distinct genetic and environmental influences. To further explore the basis for these differences, genome-wide association meta-analyses were performed to identify genetic loci that are preferentially associated with one or more skeletal regions. Variants at 13 loci (including RIN3, a novel BMD associated locus) reached genome-wide significance and several displayed evidence of differential association with BMD across the different skeletal sites in particular CPED1 and WNT16. Our results suggest that it may be advantageous to decompose the total-body BMD measures and perform GWAS at separate skeletal regions. By allowing for site-specific differences, new genetic variants affecting BMD and future risk of osteoporosis may be uncovered.
doi:10.1371/journal.pgen.1004423
PMCID: PMC4063697  PMID: 24945404
17.  Skin pigmentation, sun exposure and vitamin D levels in children of the Avon Longitudinal Study of Parents and Children 
BMC Public Health  2014;14:597.
Background
It has been hypothesised that light skin pigmentation has arisen to ensure adequate levels of vitamin D as human populations moved out of Africa and into higher latitudes. Vitamin D, which is primarily obtained through exposure to sunlight (specifically ultraviolet radiation B (UVR-B)), has been inversely associated with several complex diseases. Greater sun exposure, on the other hand, is a well-known cause of skin cancer. The potential of UVR to be beneficial for some health outcomes but detrimental for others has prompted a public health debate on how to balance the positive and negative consequences of sun exposure. In this study we aimed to determine the validity of the evolutionary hypothesis linking lighter skin with higher vitamin D concentrations in a European population. Additionally, we aimed to examine the influence of pigmentation on personal behaviour towards sunlight exposure and the effects of this behaviour on vitamin D.
Methods
We combined genetic variants strongly associated with skin colour, tanning or freckling to create genetic scores for each of these phenotypes. We examined the association of the scores with pigmentary traits, sun exposure and serum 25-hydroxyvitamin D (25(OH)D) levels among children of the Avon Longitudinal Study of Parents and Children (ALSPAC, N = 661 to 5649).
Results
We found that fairer-skinned children, i.e. those with higher pigmentation score values, had higher levels of 25(OH)D (0.6 nmol/l; 95% CI 0.2, 1.0; per unit increase in skin colour score; N = 5649). These children also used more protection against the damaging effects of UVR.
Conclusions
In this population taking protective measures against sunburn and skin cancer does not seem to remove the positive effect that having a less pigmented skin has on vitamin D production. Our findings require further replication as skin pigmentation showed only a small effect on circulating 25(OH)D.
doi:10.1186/1471-2458-14-597
PMCID: PMC4067096  PMID: 24924479
Pigmentation; Sun exposure; Vitamin D; ALSPAC; Genetic scores
18.  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
19.  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
20.  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
21.  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
22.  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
23.  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
24.  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
25.  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

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