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1.  Assessing vitamin status in large population surveys by measuring biomarkers and dietary intake – two case studies: folate and vitamin D 
Food & Nutrition Research  2012;56:10.3402/fnr.v56i0.5944.
The National Health and Nutrition Examination Survey (NHANES) provides the most comprehensive assessment of the health and nutrition status of the US population. Up-to-date reference intervals on biomarkers and dietary intake inform the scientific and public health policy communities on current status and trends over time.
The main purpose of dietary assessment methods such as the food-frequency questionnaire, food record (or diary), and 24-hr dietary recall is to estimate intake of nutrients and, together with supplement usage information, describe total intake of various foods or nutrients. As with all self-reporting methods, these tools are challenging to use and interpret. Yet, they are needed to establish dietary reference intake recommendations and to evaluate what proportion of the population meets these recommendations. While biomarkers are generally expensive and, to some degree, invasive, there is no question as to their ability to assess nutrition status. In some cases biomarkers can also be used to assess intake or function, although rarely can one biomarker fulfill all these purposes. For example, serum folate is a good indicator of folate intake, red blood cell (RBC) folate is a good status indicator, and plasma total homocysteine is a good functional indicator of one-carbon metabolism.
Using folate and vitamin D – two vitamins that are currently hotly debated in the public health arena – as two case studies, we discuss the complexities of using biomarkers and total intake information to assess nutrition status. These two examples also show how biomarkers and intake provide different information and how both are needed to evaluate and set public health policy. We also provide guidance on general requirements for using nutrition biomarkers and food and supplement intake information in longitudinal, population-based surveys.
PMCID: PMC3321254  PMID: 22489219
nutrition survey; NHANES; monitoring; trend; biochemical indicator; nutrition status; food intake; dietary questionnaire; folate; vitamin D
3.  Serum Cotinine and Whole Blood Folate Concentrations in Pregnancy 
Annals of epidemiology  2014;24(7):498-503.e1.
Prenatal tobacco smoke exposure may be associated with low maternal folate levels that increase the risk of adverse infant and child health outcomes by reducing folate availability during fetal development.
Using data from the HOME Study, we examined the relationship between secondhand or active tobacco smoke exposure and whole blood folate concentrations in pregnant women from Cincinnati, OH (n=362) at approximately 16 weeks gestation. We used multivariable linear regression to examine the association between continuous or categorical serum cotinine levels and whole blood folate levels, adjusting for sociodemographic, dietary, and perinatal variables.
After adjustment for potential confounders, an interquartile range increase in serum cotinine concentration (0.012 to 0.224 ng/mL) was suggestively associated with decreased whole blood folate levels (β:−23 nmol/L; 95% CI:−49, 3, p-value=0.08). Compared to unexposed women, reductions in mean whole blood folate were observed among active smokers (β:−94, 95% CI:−195, 6 nmol/L, p-value=0.40); smaller reductions were observed among women with secondhand exposure (β:−26; CI:−84, 32 nmol/L, p-value=0.07).
Consistent with prior studies, active smoking was associated with reduced whole blood folate levels among these pregnant women. Secondhand tobacco smoke exposures were associated with small and imprecise reductions in whole blood folate levels.
PMCID: PMC4071615  PMID: 24854185
Epidemiology; folic acid; pregnancy; tobacco smoke pollution; smoking
4.  The association between circulating total folate and folate vitamers with overall survival after post-menopausal breast cancer diagnosis 
Nutrition and cancer  2015;67(3):442-448.
We studied the relationship between plasma total folate and folate vitamer concentrations (5-methyltetrahydrofolic acid [5-methylTHF], pteroylglutamic acid [folic acid] and tetrahydrofolic acid [THF] with overall survival after breast cancer diagnosis. A secondary aim was to assess the relationship between folic acid supplement use with circulating total folate and folate vitamer concentrations. Participants were post-menopausal women diagnosed with breast cancer (n = 498) with an average follow-up of 6.7 years. Plasma total folate and folate vitamers were measured by isotope-dilution LC-MS/MS in samples collected at or post-diagnosis. Cox proportional multivariate hazards models (controlled for stage, age at diagnosis, body mass index, parity, HRT use, treatment, alcohol use, folic acid use, and energy intake), were used to assess overall survival after breast cancer diagnosis. We found that the relative risk of dying for women with plasma total folate concentrations in the highest quartile was 59% lower (HR: 0.41, 95% CI: 0.19 –0.90) compared with the lowest quartile. Data on supplement use showed that women taking folic acid supplements had significantly higher circulating total folate and folate vitamer concentrations (p < 0.0001), suggesting that increased folate consumption through diet and/or supplementation may improve prognosis after breast cancer diagnosis.
PMCID: PMC4385432  PMID: 25647689
folate; folate vitamers; breast cancer survival; epidemiological study
5.  Assessing U.S. Sodium Intake through Dietary Data and Urine Biomarkers123 
Advances in Nutrition  2013;4(5):560-562.
Sodium intake is related to blood pressure, an established risk factor for heart disease and stroke. Reducing intake may save billions in United States health care dollars annually. Efforts targeting sodium reductions make accurate monitoring vital, yet limited information exists on the accuracy of the current data to assess sodium intake in the United States population. In this symposium, new findings were presented on the accuracy of estimating population 24-h urinary excretion of sodium from spot urine specimens or sodium intake from 24-h dietary recalls. Differences in accuracy by sex, BMI, and race were apparent as well as by timing of spot urine collections. Although some published equations appear promising for estimating group means, others are biased. Individual estimates of sodium intake were highly variable and adjustment for within-individual variation in intake is required for estimating population prevalence or percentiles. Estimates indicated United States sodium intake remains high.
PMCID: PMC3771149  PMID: 24038257
6.  Blood levels of folate at birth and risk of childhood leukemia 
A role for folate in cancer etiology has long been suspected due to folate’s function as a cofactor in DNA methylation and maintenance of DNA synthesis. Previous case-control studies examining the association between risk of childhood acute lymphoblastic leukemia (ALL) and mothers’ self-reported folate intake and supplementation have been inconclusive.
Materials and Methods
We utilized a quantitative microbiologic assay to measure newborn folate concentrations in archived dried bloodspots collected at birth from 313 incident ALL cases, 44 incident acute myeloid leukemia (AML) cases, and 405 matched population-based controls.
Overall, we found no difference in hemoglobin-normalized newborn folate concentrations (HbFol, nmol/g) between ALL cases and controls (2.76 vs. 2.77, p=0.97) or between AML cases and controls (2.93 vs. 2.76, p=0.32). Null results persisted after stratification by both birth period (1982-94, 1995-98, and 1999-2002) to account for the start of folate fortification of grain products in the US, and by self-reported maternal pre-pregnancy supplement use. Similarly, no association was observed for major ALL subgroups.
Our results do not support an association between birth folate concentrations and risk of childhood AML or major ALL subgroups.
However, they do not rule out a role for folate through exposures after birth or in early stages of fetal development.
PMCID: PMC3681890  PMID: 23576692
childhood leukemia; dried blood spot specimens; California; folate
7.  Changes in the concentrations of biochemical indicators of diet and nutritional status of pregnant women across pregnancy trimesters in Trujillo, Peru, 2004–2005 
Nutrition Journal  2013;12:80.
In developing countries, deficiencies in essential micronutrients are common, particularly in pregnant women. Although, biochemical indicators of diet and nutrition are useful to assess nutritional status, few studies have examined such indicators throughout pregnancy in women in developing countries.
The primary objective of this study was to assess the nutritional status of 78 Peruvian women throughout pregnancy for 16 different nutritional indicators including fat-soluble vitamins and carotenoids, iron-status indicators, and selenium. Venous blood samples from which serum was prepared were collected during trimesters one (n = 78), two (n = 65), three (n = 62), and at term via the umbilical cord (n = 52). Questionnaires were completed to determine the demographic characteristics of subjects. Linear mixed effects models were used to study the associations between each maternal indicator and the demographic characteristics.
None of the women were vitamin A and E deficient at any stage of pregnancy and only 1/62 women (1.6%) was selenium deficient during the third trimester. However, 6.4%, 44% and 64% of women had ferritin levels indicative of iron deficiency during the first, second and third trimester, respectively. Statistically significant changes (p ≤ 0.05) throughout pregnancy were noted for 15/16 nutritional indicators for this Peruvian cohort, with little-to-no association with demographic characteristics. Three carotenoids (beta-carotene, beta-cryptoxanthin and trans-lycopene) were significantly associated with education status, while trans-lycopene was associated with age and beta-cryptoxanthin with SES (p < 0.05). Concentrations of retinol, tocopherol, beta-cryptoxanthin, lutein + zeaxanthin and selenium were lower in cord serum compared with maternal serum (p < 0.05). Conversely, levels of iron status indicators (ferritin, transferrin saturation and iron) were higher in cord serum (p < 0.05).
The increasing prevalence of iron deficiency throughout pregnancy in these Peruvian women was expected. It was surprising though not to find deficiencies in other nutrients. The results highlight the importance of continual monitoring of women throughout pregnancy for iron deficiency which could be caused by increasing fetal needs and/or inadequate iron intake as pregnancy progresses.
PMCID: PMC3685542  PMID: 23758715
Micronutrients; Pregnant women; Trimester; Serum; Cord blood; Peru
8.  Development and Certification of a Standard Reference Material for Vitamin D Metabolites in Human Seruma 
Analytical Chemistry  2011;84(2):956-962.
The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health’s Office of Dietary Supplements (NIH-ODS), has developed a Standard Reference Material (SRM) for the determination of 25-hydroxyvitamin D [25(OH)D] in serum. SRM 972 Vitamin D in Human Serum consists of four serum pools with different levels of vitamin D metabolites and has certified and reference values for 25(OH)D2, 25(OH)D3, and 3-epi-25(OH)D3. Value assignment of this SRM was accomplished using a combination of three isotope-dilution mass spectrometry approaches, with measurements performed at NIST and at the Centers for Disease Control and Prevention (CDC). Chromatographic resolution of the 3-epimer of 25(OH)D3 proved to be essential for accurate determination of the metabolites.
PMCID: PMC3287345  PMID: 22141317
10.  Biomarkers of folate status in NHANES: a roundtable summary123456 
A roundtable to discuss the measurement of folate status biomarkers in NHANES took place in July 2010. NHANES has measured serum folate since 1974 and red blood cell (RBC) folate since 1978 with the use of several different measurement procedures. Data on serum 5-methyltetrahydrofolate (5MTHF) and folic acid (FA) concentrations in persons aged ≥60 y are available in NHANES 1999–2002. The roundtable reviewed data that showed that folate concentrations from the Bio-Rad Quantaphase II procedure (Bio-Rad Laboratories, Hercules, CA; used in NHANES 1991–1994 and NHANES 1999–2006) were, on average, 29% lower for serum and 45% lower for RBC than were those from the microbiological assay (MA), which was used in NHANES 2007–2010. Roundtable experts agreed that these differences required a data adjustment for time-trend analyses. The roundtable reviewed the possible use of an isotope-dilution liquid chromatography–tandem mass spectrometry (LC-MS/MS) measurement procedure for future NHANES and agreed that the close agreement between the MA and LC-MS/MS results for serum folate supported conversion to the LC-MS/MS procedure. However, for RBC folate, the MA gave 25% higher concentrations than did the LC-MS/MS procedure. The roundtable agreed that the use of the LC-MS/MS procedure to measure RBC folate is premature at this time. The roundtable reviewed the reference materials available or under development at the National Institute of Standards and Technology and recognized the challenges related to, and the scientific need for, these materials. They noted the need for a commutability study for the available reference materials for serum 5MTHF and FA.
PMCID: PMC3127517  PMID: 21593502
11.  Biomarkers of vitamin B-12 status in NHANES: a roundtable summary123456 
A roundtable to discuss the measurement of vitamin B-12 (cobalamin) status biomarkers in NHANES took place in July 2010. NHANES stopped measuring vitamin B-12–related biomarkers after 2006. The roundtable reviewed 3 biomarkers of vitamin B-12 status used in past NHANES—serum vitamin B-12, methylmalonic acid (MMA), and total homocysteine (tHcy)—and discussed the potential utility of measuring holotranscobalamin (holoTC) for future NHANES. The roundtable focused on public health considerations and the quality of the measurement procedures and reference methods and materials that past NHANES used or that are available for future NHANES. Roundtable members supported reinstating vitamin B-12 status measures in NHANES. They noted evolving concerns and uncertainties regarding whether subclinical (mild, asymptomatic) vitamin B-12 deficiency is a public health concern. They identified the need for evidence from clinical trials to address causal relations between subclinical vitamin B-12 deficiency and adverse health outcomes as well as appropriate cutoffs for interpreting vitamin B-12–related biomarkers. They agreed that problems with sensitivity and specificity of individual biomarkers underscore the need for including at least one biomarker of circulating vitamin B-12 (serum vitamin B-12 or holoTC) and one functional biomarker (MMA or tHcy) in NHANES. The inclusion of both serum vitamin B-12 and plasma MMA, which have been associated with cognitive dysfunction and anemia in NHANES and in other population-based studies, was preferable to provide continuity with past NHANES. Reliable measurement procedures are available, and National Institute of Standards and Technology reference materials are available or in development for serum vitamin B-12 and MMA.
PMCID: PMC3127527  PMID: 21593512
12.  Serum 25-hydroxyvitamin D status of the US population: 1988–1994 versus 2000–20041 
Changes in serum 25-hydroxyvitamin D (25OHD) concentrations in the US population have not been described.
Use data from the National Health and Nutrition Examination Surveys (NHANES) to compare serum 25OHD concentrations in the US population in 2000–2004 versus 1988–1994, and to identify contributing factors.
Serum 25OHD was measured with a radioimmunoassay kit in 20,289 participants in NHANES 2000–2004 and 18,158 participants in NHANES III (1988–1994). Body mass index (BMI) was calculated from measured height and weight. Milk intake and sun protection were assessed by questionnaire. Assay differences were assessed by re-analyzing 150 stored sera specimens from NHANES III with the current assay.
Age-adjusted mean serum 25OHD concentrations were significantly lower by 5–20 nmol/L in NHANES 2000–2004 than in NHANES III. After accounting for assay shifts, age-adjusted means in NHANES 2000–2004 remained significantly lower (by 5–9 nmol/L) in most males, but not in most females. In a study subsample, accounting for the confounding effects of assay differences changed mean serum 25OHD by ~10 nmol/L, while accounting for changes in the factors likely related to real changes in vitamin D status (BMI, milk intake, and sun protection) changed means by 1–1.6 nmol/L.
Overall, mean serum 25OHD was lower in 2000–2004 than 1988–1994. Assay changes unrelated to changes in vitamin D status accounted for much of the difference in most population groups. In an adult subgroup, combined changes in BMI, milk intake and sun protection appeared to contribute to a real decline in vitamin D status.
PMCID: PMC2745830  PMID: 19064511
Serum 25-hydroxyvitamin D; Vitamin D status; NHANES
13.  Pilot Study of Urinary Biomarkers of Phytoestrogens, Phthalates, and Phenols in Girls 
Environmental Health Perspectives  2006;115(1):116-121.
Hormonally active environmental agents have been measured among U.S. children using exposure biomarkers in urine. However, little is known about their variation by race, age, sex, and geography, and no data exist for newly developed biomarkers.
Our goal was to characterize relevant, prevalent exposures for a study of female pubertal development.
In a pilot study among 90 girls from New York City, New York, Cincinnati, Ohio, and northern California, we measured 25 urinary analytes representing 22 separate agents from three chemical families: phytoestrogens, phthalates, and phenols. Exposures occur chiefly from the diet and from household or personal care products.
Participants represented four racial/ethnic groups (Asian, black, Hispanic, white), with mean age of 7.77 years. Most analytes were detectable in > 94% of samples. The highest median concentrations for individual analytes in each family were for enterolactone (298 μg/L), monoethylphthalate (MEP; 83.2 μg/L), and benzophenone-3 (BP3; 14.7 μg/L). Few or no data have been reported previously for four metabolites: mono(2-ethyl-5-carboxypentyl) phthalate, triclosan, bisphenol A (BPA), and BP3; these were detected in 67–100% of samples with medians of 1.8–53.2 μg/L. After multivariate adjustment, two analytes, enterolactone and BPA, were higher among girls with body mass index < 85th reference percentile than those at or above the 85th percentile. Three phthalate metabolites differed by race/ethnicity [MEP, mono(2-ethylhexyl) phthalate, and mono-3-carboxypropylphthalate].
A wide spectrum of hormonally active exposure biomarkers were detectable and variable among young girls, with high maximal concentrations (> 1,000 μg/L) found for several analytes. They varied by characteristics that may be relevant to development.
PMCID: PMC1797844  PMID: 17366830
biomarkers; children; exposure; phenols; phthalates; phytoestrogen; urine

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