Is there a reverse J-shaped association between 25-hydroxyvitamin D and all-cause mortality? Results from the U.S. nationally representative NHANES.

Context: A reverse J-shaped association between serum 25-hydroxyvitamin D (25[OH]D) concentration and all-cause mortality was suggested in a 9-year follow-up (1991-2000) analysis of the Third National Health and Nutrition Examination Survey (NHANES III, 1988-1994).

Objective: Our objective was to repeat the analyses with 6 years additional follow-up to evaluate whether the association persists through 15 years of follow-up.

Participants: The study included 15 099 participants aged ≥ 20 years with 3784 deaths.

Development and certification of a standard reference material for vitamin D metabolites in human serum.

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)D(2), 25(OH)D(3), and 3-epi-25(OH)D(3). 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).

Vitamin D in pregnancy and lactation in humans.

Concerns exist about the adequacy of vitamin D in pregnant and lactating women. This review assesses the evidence that maternal vitamin D status influences maternal, fetal, and breast-fed infant bone health; maternal adverse outcomes (preeclampsia, gestational diabetes, obstructed labor, and infectious disease); fetal adverse outcomes (growth, gestational age, and developmental programming); and infant adverse outcomes. The evidence for all of these outcomes is contradictory (except for maternal infectious disease) and lacking causality; thus, it is inconclusive.

Comparison of serum and red blood cell folate microbiologic assays for national population surveys.

Three laboratories participated with their laboratory-specific microbiologic growth assays (MA) in the NHANES 2007-2008 to assess whether the distributions of serum (n = 2645) and RBC folate (n = 2613) for the same one-third sample of participants were comparable among laboratories. Laboratory (L) 2 produced the highest and L1 the lowest serum and RBC folate geometric means (nmol/L) in the NHANES sample (serum: L1, 39.5; L2, 59.

Biomarkers of vitamin B-12 status in NHANES: a roundtable summary.

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.

Biomarkers of folate status in NHANES: a roundtable summary.

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.

Dietary supplement use among U.S. adults has increased since NHANES III (1988-1994).

Use of dietary supplements is common among the U.S. adult population.

Dietary supplement use in the United States, 2003-2006.

Dietary supplement use has steadily increased over time since the 1970s; however, no current data exist for the U.S. population.

NHANES monitoring of serum 25-hydroxyvitamin D: a roundtable summary.

A roundtable to discuss monitoring of serum 25-hydroxyvitamin D [25(OH)D] in the NHANES was held in late July 2009. Topics included the following: 1) options for dealing with assay fluctuations in serum 25(OH)D in the NHANES conducted between 1988 and 2006; 2) approaches for transitioning between the RIA used in the NHANES between 1988 and 2006 to the liquid chromatography tandem MS (LC-MS/MS) measurement procedure to be used in NHANES 2007 and later; 3) approaches for integrating the recently available standard reference material for vitamin D in human serum (SRM 972) from the National Institute of Standards and Technology (NIST) into the NHANES; 4) questions regarding whether the C-3 epimer of 25-hydroxyvitamin D3 [3-epi-25(OH)D3] should be measured in NHANES 2007 and later; and 5) identification of research and educational needs. The roundtable experts agreed that the NHANES data needed to be adjusted to control for assay fluctuations and offered several options for addressing this issue.

Unmetabolized serum folic acid and its relation to folic acid intake from diet and supplements in a nationally representative sample of adults aged > or =60 y in the United States.

Background: Unmetabolized serum folic acid (UMFA) has been detected in adults. Previous research indicates that high folic acid intakes may be associated with risk of cancer.

Objective: The objective was to examine UMFA concentrations in relation to dietary and supplemental folate and status biomarkers in the US population aged > or =60 y.

Total folate and folic acid intakes from foods and dietary supplements of US children aged 1-13 y.

Background: Total folate intake includes naturally occurring food folate and folic acid from fortified foods and dietary supplements. Recent reports have focused on total folate intakes of persons aged > or =14 y. Information on total folate intakes of young children, however, is limited.

Estimation of total usual calcium and vitamin D intakes in the United States.

Our objective in this study was to estimate calcium intakes from food, water, dietary supplements, and antacids for U.S. citizens aged >or=1 y using NHANES 2003-2006 data and the Dietary Reference Intake panel age groupings.

Three-phase model harmonizes estimates of the maximal suppression of parathyroid hormone by 25-hydroxyvitamin D in persons 65 years of age and older.

The concentration or threshold of 25-hydroxyvitamin D [25(OH)D] needed to maximally suppress intact serum parathyroid hormone (iPTH) has been suggested as a measure of optimal vitamin D status. Depending upon the definition of maximal suppression of iPTH and the 2-phase regression approach used, 2 distinct clusters for a single 25(OH)D threshold have been reported: 16-20 ng/mL (40-50 nmol/L) and 30-32 ng/mL (75-80 nmol/L). To rationalize the apparently disparate published results, we compared thresholds from several regression models including a 3-phase one to estimate simultaneously 2 thresholds before and after adjusting for possible confounding for age, BMI, glomerular filtration rate, dietary calcium, and season (April-September vs.

Total folate and folic acid intake from foods and dietary supplements in the United States: 2003-2006.

Background: The term total folate intake is used to represent folate that occurs naturally in food as well as folic acid from fortified foods and dietary supplements. Folic acid has been referred to as a double-edged sword because of its beneficial role in the prevention of neural tube defects and yet possible deleterious effects on certain cancers and cognitive function. Previous monitoring efforts did not include folic acid from dietary supplements and are therefore not complete.

Vitamin B-6 intake is inversely related to, and the requirement is affected by, inflammation status.

Low circulating pyridoxal 5'-phosphate (PLP) concentrations have been linked to inflammatory markers and the occurrence of inflammatory diseases. However, the implications of these findings are unclear. The measurement of PLP and C-reactive protein (CRP) in blood samples collected from participants in the 2003-2004 NHANES afforded us the opportunity to investigate this relationship in the general U.

Use of dietary supplements by pregnant and lactating women in North America.

Nutrient requirements increase during periods of growth and development such as pregnancy and lactation. In response, many clinicians recommend dietary supplements during these important periods of the life cycle. Although there exist some recommendations concerning the need for a limited number of nutrients in supplemental form (eg, iron, folic acid, and iodine), there is a relative paucity of data concerning the use of dietary supplements during pregnancy and lactation.

Serum 25-hydroxyvitamin D status of the US population: 1988-1994 compared with 2000-2004.

Background: Changes in serum 25-hydroxyvitamin D [25(OH)D] concentrations in the US population have not been described.

Objective: We used data from the National Health and Nutrition Examination Surveys (NHANES) to compare serum 25(OH)D concentrations in the US population in 2000-2004 with those in 1988-1994 and to identify contributing factors.

Design: Serum 25(OH)D was measured with a radioimmunoassay kit in 20 289 participants in NHANES 2000-2004 and in 18 158 participants in NHANES III (1988-1994).

Summary of roundtable discussion on vitamin D research needs.

We summarize the discussions of a roundtable following the conference "Vitamin D and Health in the 21st Century: an Update." The roundtable participants offered additional information on vitamin D research needs from a critical, impartial, and interdisciplinary perspective. Although the group recognized the progress to date, they found that the available evidence on the relation of 25-hydroxyvitamin D, dietary intake, status, functional health, and adverse outcomes has significant limitations because most studies have been short term, have failed to consider important confounders such as baseline vitamin D status and body mass index, and did not study key populations.

Overview of the conference "Vitamin D and Health in the 21st Century: an Update".

We summarize the key findings, strength of the evidence, and research needs identified in the National Institutes of Health conference "Vitamin D and Health in the 21st Century: an Update," which was held in September 2007; a systematic evidence-based review; and a National Institutes of Health roundtable discussion held after the conference by scientists with relevant expertise. The evidence-based review addressed 5 questions on 25-hydroxyvitamin D [25(OH)D] and functional outcomes across the life cycle and response to exposure, bone health outcomes of supplementation, risks and benefits of sun exposure, and adverse outcomes. These questions also framed the conference and roundtable discussions.

Plasma pyridoxal 5'-phosphate in the US population: the National Health and Nutrition Examination Survey, 2003-2004.

Background: No large-scale, population-based study has considered the descriptive epidemiology of vitamin B-6 status with use of plasma pyridoxal 5'-phosphate (PLP), the indicator of vitamin B-6 adequacy used to set the current Recommended Dietary Allowance, which is < or = 2 mg/d for all subgroups.

Objectives: We sought to examine the epidemiology of vitamin B-6 status in the US population.

Methods: In > 6000 participants aged > or = 1 y in the National Health and Nutrition Examination Survey (2003-2004), we considered relations between plasma PLP and various subject characteristics and examined trends in plasma PLP and homocysteine with vitamin B-6 intake, both overall and in selected subgroups.

Trends in circulating concentrations of total homocysteine among US adolescents and adults: findings from the 1991-1994 and 1999-2004 National Health and Nutrition Examination Surveys.

Background: The National Health and Nutrition Examination Survey (NHANES) has monitored total homocysteine (tHcy) concentrations in a nationally-representative sample of the US population since 1991. Until recently, however, data could not be compared across survey periods because of changes in analytical methods and specimen matrices. Such an analysis of these data could supplement current knowledge regarding whether the US folic acid fortification program has modified national plasma tHcy concentrations.