National Estimates of Serum Total 25-Hydroxyvitamin D and Metabolite Concentrations Measured by Liquid Chromatography-Tandem Mass Spectrometry in the US Population during 2007-2010.

BACKGROUND: The 2007-2010 NHANES provides the first US nationally representative serum 25-hydroxyvitamin D [25(OH)D] concentrations measured by standardized liquid chromatography-tandem mass spectrometry. OBJECTIVE: We describe patterns for total 25(OH)D and individual metabolites in persons aged ≥1 y stratified by race-ethnicity and grouped by demographic, intake, physiologic, and lifestyle variables. METHODS: We measured 25-hydroxycholecalciferol [25(OH)D3], 25-hydroxyergocalciferol [25(OH)D2], and C3-epimer of 25(OH)D3 [C3-epi-25(OH)D3] in serum samples (n = 15,652) from the 2007-2010 cross-sectional NHANES [total 25(OH)D = 25(OH)D3 + 25(OH)D2]. RESULTS: Concentrations (median, detection rate) of 25(OH)D3 (63.6 nmol/L, 100%) and C3-epi-25(OH)D3 (3.40 nmol/L, 86%) were generally detectable; 25(OH)D2 was detectable in 19% of the population. Total 25(OH)D, 25(OH)D3, and C3-epi-25(OH)D3 displayed similar demographic patterns and were strongly correlated (Spearman's r > 0.70). Concentrations of 25(OH)D2 (90th percentile) were much higher in persons aged ≥60 y (17.3 nmol/L) than in younger age groups (≤4.88 nmol/L). We noted significant race-ethnicity differences in mean total 25(OH)D [non-Hispanic blacks (NHBs), Hispanics, and non-Hispanic whites (NHWs): 46.6, 57.2, and 75.2 nmol/L, respectively] and in the prevalence of total 25(OH)D <30 nmol/L overall (24% of NHBs, 6.4% of Hispanics, and 2.3% of NHWs) as well as stratified by season (winter months: 30% of NHBs, 7.5% of Hispanics, and 3.8% of NHWs; summer months: 17% of NHBs, 4.4% of Hispanics, and 1.6% of NHWs). Persons with higher vitamin D intakes (diet, supplements, or both) and those examined during May-October had significantly higher total 25(OH)D. Significant race-ethnicity interactions in a multiple linear regression model confirmed the necessity of providing race-ethnicity-specific estimates of total 25(OH)D. CONCLUSIONS: Race-ethnicity differences in the prevalence of low total 25(OH)D remained strong even after adjustment for season to account for the NHANES design imbalance between season, latitude, and race-ethnicity. The strong correlation between C3-epi-25(OH)D3 and 25(OH)D3 may be because the epimer is a metabolite of 25(OH)D3. The presence of 25(OH)D2 mainly in older persons is likely a result of high-dose prescription vitamin D2.

Use and applications of systematic reviews in public health nutrition.

Decisions related to a spectrum of nutrition-related public health and clinical concerns must consider many factors and are best informed by evaluating the totality and quality of the evidence. Systematic review (SR) is a structured process to evaluate, compare, and synthesize relevant evidence for the SR-specific question(s). Applications of SR are exemplified here through the discussion of four case studies: research agendas, nutrient reference intakes, dietary guidance, and practice guidelines. Concerns that SR cannot be effectively applied to nutrition evidence because of the lack of an unexposed comparator and the complex homeostasis in nutrition are discussed. Central to understanding the applicability of SR is its flexibility in defining key inclusion criteria and rigorous elements as appropriate for the SR-specific question(s). Through the reduction of bias and random error by explicit, reproducible, comprehensive, and rigorous examination of all of the evidence, SR informs the scientific judgment needed for sound evidence-based public health nutrition.

Use of Folate-Based and Other Fortification Scenarios Illustrates Different Shifts for Tails of the Distribution of Serum 25-Hydroxyvitamin D Concentrations.

BACKGROUND: The purpose of food fortification is to affect those at the lower end of the distribution curve for nutrient status while avoiding unintended consequences for those at the high end of the distribution. Vitamin D presents challenges in this regard. OBJECTIVES: We used scenarios to model changes in concentrations of serum 25-hydroxyvitamin D [25(OH)D] based on increases made because of assumptions about fortification. We then examined the outcomes for balance between improving serum 25(OH)D status for those at risk of inadequacy while avoiding high concentrations for those not at risk. METHODS: Data from NHANES 2001-2006 served as baseline serum 25(OH)D concentrations and were used to model shifts in serum 25(OH)D distribution after application of 3 fortification scenarios, including conceptual scenarios and an experiential predictive scenario we developed with the use of statistical modeling of changes in NHANES serum folate concentrations between prefortification and postfortification time periods. RESULTS: All scenarios suggested the possibility of increasing serum 25(OH)D above 125 nmol/L among the proportion of the population at the high end of baseline serum 25(OH)D distribution. The scenario based on serum folate change struck a middle ground between the 2 conceptual scenarios. It predicted a prevalence of 11% <40 nmol/L serum 25(OH)D compared with 17% currently (study baseline), and 8% prevalence of serum 25(OH)D >125 nmol/L compared with <1% currently (study baseline). It also confirmed that fortification affects those at the low end of the status distribution curve differently from those at the high end. CONCLUSIONS: Nutrient inadequacy of the type demonstrated by vitamin D--in which the risk is not universal--requires a thorough exploration of the unintended consequences of the overall shift in the distribution of serum 25(OH)D if efforts are made to use fortification to increase the status of persons at risk of deficiency. Fortification is at best a blunt instrument that must be implemented with caution. Moreover, fortification must be preceded by more research to elucidate the dose-response relation between intake and changes in serum 25(OH)D.

Including food 25-hydroxyvitamin D in intake estimates may reduce the discrepancy between dietary and serum measures of vitamin D status.

The discrepancy between the commonly used vitamin D status measures-intake and serum 25-hydroxyvitamin D [25(OH)D] concentrations--has been perplexing. Sun exposure increases serum 25(OH)D concentrations and is often used as an explanation for the higher population-based serum concentrations in the face of apparently low vitamin D intake. However, sun exposure may not be the total explanation. 25(OH)D, a metabolite of vitamin D, is known to be present in animal-based foods. It has been measured and reported only sporadically and is not currently factored into U.S. estimates of vitamin D intake. Previously unavailable preliminary USDA data specifying the 25(OH)D content of a subset of foods allowed exploration of the potential change in the reported overall vitamin D content of foods when the presence of 25(OH)D was included. The issue of 25(OH)D potency was addressed, and available commodity intake estimates were used to outline trends in projected vitamin D intake when 25(OH)D in foods was taken into account. Given the data available, there were notable increases in the total vitamin D content of a number of animal-based foods when potency-adjusted 25(OH)D was included, and in turn there was a potentially meaningful increase (1.7-2.9 µg or 15-30% of average requirement) in vitamin D intake estimates. The apparent increase could reduce discrepancies between intake estimates and serum 25(OH)D concentrations. The relevance to dietary interventions is discussed, and the need for continued exploration regarding 25(OH)D measurement is highlighted.

Critical data at the crossroads: the National Health and Nutrition Examination Survey faces growing challenges.

NHANES needs urgent attention to ensure its future, which is facing emerging challenges associated with data collection, stagnant funding that has undercut innovation, and the increased call for granular data for subpopulations and groups at risk. The concerns do not rest merely on securing more funding but focus on the need for a constructive review of the survey to explore new approaches and identify appropriate change. This white paper, developed under the auspices of the ASN's Committee on Advocacy and Science Policy (CASP), is a call to the nutrition community to advocate for and support activities to prepare NHANES for future success in a changing nutrition world. Furthermore, because NHANES is much more than a nutrition survey and serves the needs of many in health fields and even commercial arenas, effective advocacy must be grounded in alliances among the survey's diverse stakeholders so that the full range of expertise and interests can engage. This article highlights the complicated nature of the survey along with key overarching challenges to underscore the importance of a measured, thoughtful, comprehensive, and collaborative approach to considering the future of NHANES. Starting-point questions are identified for the purposes of focusing dialog, discussion forums, and research. In particular, the CASP calls for a National Academies of Sciences, Engineering, and Medicine study on NHANES to articulate an actionable framework for NHANES going forward. With a well-informed and integrated set of goals and recommendations that could be provided by such a study, a secure future for NHANES is more readily achievable.

Perspectives and progress on upper levels of intake in the United States.

In the US, recognition of the appropriateness of including an upper level of intake estimate among reference values for nutrient substances was made in 1994 when the Food and Nutrition Board of the Institute of Medicine (IOM) specified the inclusion of an "upper safe" level among its proposed reference points for intake of nutrients and food components. By 1998, a group convened by the IOM had established a risk assessment model for establishing upper intake levels for nutrients, eventually termed the tolerable upper intake levels (UL). A risk assessment framework (i.e., a scientific undertaking intended to characterize the nature and likelihood of harm resulting from human exposure to agents in the environment), as developed in other fields of study, was a logical fit for application to nutrients. But importantly, whereas risk assessment requires that information be organized in specific ways, it does not require specific scientific evaluation methods. Rather, it makes transparent and documents the decision-making that occurs given the available data and the related uncertainties. During the 1990s and beyond, the various IOM committees charged with developing UL for a range of nutrients utilized the risk assessment framework, making modifications and adjustments as dictated by the data. This experience informed the general organizational process for establishing UL but also underscored the dearth of data. For many reasons, undertaking scientific research and obtaining data about the effects of excessive intake have been challenging. It is time to consider creative and focused strategies for modeling, simulating, and otherwise studying the effects of excessive intake of nutrient substances.

Summary of workshop discussions on establishing upper limits for amino acids with specific attention to available data for the essential amino acids leucine and tryptophan.

The morning of the first day of the 8th Amino Acid Assessment Workshop was organized and co-sponsored by the International Council on Amino Acid Science (ICAAS) and the International Life Sciences Institute Research Foundation and was focused on the International Life Sciences Institute Research Foundation's approach to establishing upper limits of nutrients. The remainder of d 1 and all of d 2 were focused on the safety of leucine and tryptophan, with special emphasis on determining the upper level of the safe range of intake. It was recognized that some toxicological frameworks, mainly the key-events dose response framework, might be applicable to amino acids and provide appropriate assistance to regulators in establishing upper limits for amino acids as a group of nutrients used in dietary supplements. ICAAS-funded projects for determining the upper intake limits for the essential amino acid leucine provided the main pool of leucine data discussed at the workshop. The acute clinical study suggests 500 mg/(kg · d) as a possible upper limit for leucine in healthy humans, but the safety margin needed to widen this limit to the general population has not been determined. For tryptophan, the workshop participants found less ground for consensus. Older efficacy studies suggested that tryptophan at 8-15 g/d was well tolerated, but human research was abruptly terminated in the late 1980s and no new data are available. Animal results obtained in pigs and rodents were discussed and 2 possible strategies for applying those outcomes to humans were described.

Nutrient risk assessment as a tool for providing scientific assessments to regulators.

Regulatory officials world-wide are paying attention to the process for establishing the upper level of intake for nutrient substances. The rapidly expanding use of dietary supplements, fortified foods, and functional foods, coupled with increased trade in these products, has focused attention on ensuring their safety and on harmonizing standards internationally. The more traditional approaches, in which the regulators either provided no standards for upper levels of intake or developed standards based on some arbitrary multiple of the intake level known to provide an adequate amount of the nutrient, are recognized as outdated or inappropriate for the emerging issues. Preferred approaches are those that rely on the systematic scientific assessment of risk to determine the levels of intake below which no harm may occur. The scientific study of risk is playing an increased role in establishing the regulatory upper levels of "safe" nutrient intake. Risk assessment, as a component of risk analysis, offers a scientific basis for regulatory decision-making regarding the regulators' task associated with specifying safe upper levels of intake for nutrient substances. This article describes the key components of risk assessment as they are applied within the nutrition field. Although regulatory frameworks vary from country to country and all countries retain their right to determine their own level of protection, regulatory systems operate most effectively and are more likely to converge toward harmonization if they are informed by independent, organized, and scientific reviews that are conducted systematically in a transparent manner.

Introduction to workshop on iron screening and supplementation in iron-replete pregnant women and young children.

The NIH Office of Dietary Supplements convened a public workshop on iron screening and supplementation in iron-replete pregnant women and young children in 2016 in Bethesda, Maryland. The starting point for the workshop was the recent reports from the US Preventive Services Task Force concluding that there was insufficient evidence to evaluate the benefits and harms associated with iron screening and routine supplementation among asymptomatic pregnant women and young children (6-24 mo old) in the United States. The goal of the workshop was to explore and refine understanding about the existing knowledge gaps and research needs associated with these preventive services for these groups. Given the focus on the United States, planning for the workshop took into account the higher iron status in the United States compared with developing countries and, in turn, included a focus on iron-replete individuals consistent with the U-shaped risk curve for nutrient-health relations. Topic areas included adaptations in iron homeostasis associated with pregnancy and young childhood, the impact of inflammation, measurement of iron status, current estimates of iron status for pregnant women and young children in the United States and in Europe, and emerging evidence suggesting adverse effects associated with iron supplementation of iron-replete individuals. A crosscutting dialogue conducted at the close of the workshop formed the basis for a workshop summary that specified evidence gaps and research needs in a range of areas centered on the relation of these adaptations of iron homeostasis with the response to and risk from iron supplementation as well as the need for indicators informative of the full continuum of iron status and based on health outcomes, not just erythropoiesis.

Iron Supplementation during Pregnancy and Infancy: Uncertainties and Implications for Research and Policy.

Iron is particularly important in pregnancy and infancy to meet the high demands for hematopoiesis, growth and development. Much attention has been given to conditions of iron deficiency (ID) and iron deficient anemia (IDA) because of the high global prevalence estimated in these vulnerable life stages. Emerging and preliminary evidence demonstrates, however, a U-shaped risk at both low and high iron status for birth and infant adverse health outcomes including growth, preterm birth, gestational diabetes, gastrointestinal health, and neurodegenerative diseases during aging. Such evidence raises questions about the effects of high iron intakes through supplementation or food fortification during pregnancy and infancy in iron-replete individuals. This review examines the emerging as well as the current understanding of iron needs and homeostasis during pregnancy and infancy, uncertainties in ascertaining iron status in these populations, and issues surrounding U-shaped risk curves in iron-replete pregnant women and infants. Implications for research and policy are discussed relative to screening and supplementation in these vulnerable populations, especially in developed countries in which the majority of these populations are likely iron-replete.

Integrating themes, evidence gaps, and research needs identified by workshop on iron screening and supplementation in iron-replete pregnant women and young children.

This report addresses the evidence and the uncertainties, knowledge gaps, and research needs identified by participants at the NIH workshop related to iron screening and routine iron supplementation of largely iron-replete pregnant women and young children (6-24 mo) in developed countries. The workshop presentations and panel discussions focused on current understanding and knowledge gaps related to iron homeostasis, measurement of and evidence for iron status, and emerging concerns about supplementing iron-replete members of these vulnerable populations. Four integrating themes emerged across workshop presentations and discussion and centered on 1) physiologic or developmental adaptations of iron homeostasis to pregnancy and early infancy, respectively, and their implications, 2) improvement of the assessment of iron status across the full continuum from iron deficiency anemia to iron deficiency to iron replete to iron excess, 3) the linkage of iron status with health outcomes beyond hematologic outcomes, and 4) the balance of benefit and harm of iron supplementation of iron-replete pregnant women and young children. Research that addresses these themes in the context of the full continuum of iron status is needed to inform approaches to the balancing of benefits and harms of screening and routine supplementation.

Iron status in pregnant women and women of reproductive age in Europe.

Understanding the iron status in pregnant women in Europe provides a foundation for considering the role of iron screening and supplementation. However, available reports and studies have used different approaches that challenge the devising of overall summaries. Moreover, data on pregnant women are limited, and thus, data on women of reproductive age provide useful background information including baseline iron stores in pregnant women. This review considered data that are available from >15 European countries including national surveys and relevant clinical studies. In European women of reproductive age, median or geometric mean serum ferritin (SF) concentrations were estimated at 26-38 µg/L. Approximately 40-55% of this population had small or depleted iron stores (i.e., SF concentration ≤30 µg/L), and 45-60% of this population had apparently replete iron stores. The prevalence of iron deficiency (ID) and iron deficiency anemia (IDA) was 10-32% and 2-5%, respectively, depending on the cutoffs used. Approximately 20-35% of European women of reproductive age had sufficient iron stores (SF concentration >70 µg/L) to complete a pregnancy without supplementary iron. During pregnancy, European women in controlled supplementation trials who were not receiving iron supplements displayed increasing prevalences of ID and IDA during pregnancy, which peaked in the middle to late third trimester. Available evidence has suggested that, in gestational weeks 32-39, the median or geometric mean SF concentrations were 6-21 µg/L, and prevalences of ID and IDA were 28-85% and 21-35%, respectively. Women who were taking iron supplements had higher iron status and lower prevalences of ID and IDA, which were dependent on the dose of iron and compliance. The data suggest that, in Europe, the iron status of reproductive-aged women varies by region and worsens in pregnancy without iron supplementation.

Vitamin D: Moving Forward to Address Emerging Science.

The science surrounding vitamin D presents both challenges and opportunities. Although many uncertainties are associated with the understandings concerning vitamin D, including its physiological function, the effects of excessive intake, and its role in health, it is at the same time a major interest in the research and health communities. The approach to evaluating and interpreting the available evidence about vitamin D should be founded on the quality of the data and on the conclusions that take into account the totality of the evidence. In addition, these activities can be used to identify critical data gaps and to help structure future research. The Office of Dietary Supplements (ODS) at the National Institutes of Health has as part of its mission the goal of supporting research and dialogues for topics with uncertain data, including vitamin D. This review considers vitamin D in the context of systematically addressing the uncertainty and in identifying research needs through the filter of the work of ODS. The focus includes the role of systematic reviews, activities that encompass considerations of the totality of the evidence, and collaborative activities to clarify unknowns or to fix methodological problems, as well as a case study using the relationship between cancer and vitamin D.

Correspondence of folate dietary intake and biomarker data.

Background: Public health concerns with regard to both low and high folate status exist in the United States. Recent publications have questioned the utility of self-reported dietary intake data in research and monitoring.Objectives: The purpose of this analysis was to examine the relation between self-reported folate intakes and folate status biomarkers and to evaluate their usefulness for several types of applications.Design: We examined usual dietary intakes of folate by using the National Cancer Institute method to adjust two 24-h dietary recalls (including dietary supplements) for within-person variation and then compared these intakes with serum and red blood cell (RBC) folate among 4878 men and nonpregnant, nonlactating women aged ≥19 y in NHANES 2011-2012, a nationally representative, cross-sectional survey, with respect to consistency across prevalence estimates and rank order comparisons.Results: There was a very low prevalence (<1%) of folate deficiency when serum (<7 nmol/L) and RBC (<305 nmol/L) folate were considered, whereas a higher proportion of the population reported inadequate total dietary folate intakes (6%). Similar patterns of change occurred between intakes and biomarkers of folate status when distributions were examined (i.e., dose response), particularly when diet was expressed in µg. Intakes greater than the Tolerable Upper Intake Level greatly increased the odds of having high serum folate (OR: 17.6; 95% CI: 5.5, 56.0).Conclusions: When assessing folate status in the United States, where fortification and supplement use are common, similar patterns in the distributions of diet and biomarkers suggest that these 2 types of status indicators reflect the same underlying folate status; however, the higher prevalence estimates for inadequate intakes compared with biomarkers suggest, among other factors, a systematic underestimation bias in intake data. Caution is needed in the use of dietary folate data to estimate the prevalence of inadequacy among population groups. The use of dietary data for rank order comparisons or to estimate the potential for dietary excess is likely more reliable.

Developmental Ethanol Exposure Leads to Long-Term Deficits in Attention and Its Underlying Prefrontal Circuitry.

Chronic prenatal exposure to ethanol can lead to a spectrum of teratogenic outcomes that are classified in humans as fetal alcohol spectrum disorders (FASD). One of the most prevalent and persistent neurocognitive components of FASD is attention deficits, and it is now thought that these attention deficits differ from traditional attention deficit hyperactivity disorder (ADHD) in their quality and response to medication. However, the neuronal mechanisms underlying attention deficits in FASD are not well understood. We show here that after developmental binge-pattern ethanol exposure, adult mice exhibit impaired performance on the five-choice serial reaction time test for visual attention, with lower accuracy during initial training and a higher rate of omissions under challenging conditions of high attention demand. Whole-cell electrophysiology experiments in these same mice find dysregulated pyramidal neurons in layer VI of the medial prefrontal cortex, which are critical for normal attention performance. Layer VI neurons show decreased intrinsic excitability and increased responses to stimulation of both nicotinic acetylcholine receptors and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors. Moreover, although nicotinic acetylcholine responses correlate with performance on the five-choice task in control mice, these relationships are completely disrupted in mice exposed to ethanol during development. These findings demonstrate a novel outcome of developmental binge-pattern ethanol exposure and suggest that persistent alterations to the function of prefrontal layer VI neurons play an important mechanistic role in attention deficits associated with FASD.

Interlaboratory Trial for Measurement of Vitamin D and 25-Hydroxyvitamin D [25(OH)D] in Foods and a Dietary Supplement Using Liquid Chromatography-Mass Spectrometry.

Assessment of total vitamin D intake from foods and dietary supplements (DSs) may be incomplete if 25-hydroxyvitamin D [25(OH)D] intake is not included. However, 25(OH)D data for such intake assessments are lacking, no food or DS reference materials (RMs) are available, and comparison of laboratory performance has been needed. The primary goal of this study was to evaluate whether vitamin D3 and 25(OH)D3 concentrations in food and DS materials could be measured with acceptable reproducibility. Five experienced laboratories from the United States and other countries participated, all using liquid chromatography tandem-mass spectrometry but no common analytical protocol; however, various methods were used for determining vitamin D3 in the DS. Five animal-based materials (including three commercially available RMs) and one DS were analyzed. Reproducibility results for the materials were acceptable. Thus, it is possible to obtain consistent results among experienced laboratories for vitamin D3 and 25(OH)D3 in foods and a DS.

Questions About Vitamin D for Primary Care Practice: Input From an NIH Conference.

There is considerable consumer and physician interest in vitamin D as a possible therapeutic agent for a range of clinical conditions and, despite mixed evidence, the interest does not appear to lessen. Some clinicians believe that consumption of vitamin D is inadequate and, in turn, advocate vitamin D supplementation to increase serum levels of the nutrient. However, evidence concerning the role of vitamin D in health and disease is conflicting, and primary care physicians have little time to sort through the data and may find it difficult to advise their patients. To better understand the challenges that primary care physicians face regarding vitamin D, and to help inform those who provide guidance for clinical decision-making, the Office of Dietary Supplements at the National Institutes of Health, with co-sponsorship from other federal health agencies, held a conference titled Vitamin D: Moving Toward Evidence-based Decision Making in Primary Care in December 2014. More than 20 invited presenters and panelists considered laboratory methods for measuring vitamin D status, discussed how clinical studies of vitamin D should be evaluated and used in developing recommendations, noted the role of values and preferences in clinical decision-making, debated the current science related to at-risk groups, and described emerging data about health risks of excessive intakes of vitamin D. Eight questions about vitamin D stem from the Conference presentations as well as other expert sources.