[For a commentary on this report, recommending it “be required reading for all nutritionists, clinicians, and vitamin D aficionados who are decision makers with regard to 25(OH)D assays, vitamin D nutritional policy, and the care of patients with vitamin D-related diseases,” see the corresponding editorial “A vitamin D nutritional cornucopia: New insights concerning the serum 25-hydroxyvitam D status of the US population,” by vitamin D expert Anthony W. Norman at University of California-Riverside.]
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). 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 serum specimens from NHANES III with the current assay.
Results: Age-adjusted mean serum 25(OH)D concentrations were 5–20 nmol/L lower in NHANES 2000–2004 than in NHANES III. After adjustment 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, adjustment for the confounding effects of assay differences changed mean serum 25(OH)D concentrations by [about] 10 nmol/L, and adjustment for changes in the factors likely related to real changes in vitamin D status (i.e., BMI [body mass index], milk intake, and sun protection) changed mean serum 25(OH)D concentrations by 1–1.6 nmol/L.
Conclusions: Overall, mean serum 25(OH)D 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.
[Authors' Note:] The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention, the National Institutes of Health, or the US Department of Health and Human Services. Reprints are not available. Address correspondence to AC Looker - e-mail email@example.com.
Source: American Journal of Clinical Nutrition, Dec 1, 2008;88(6) 1519-1527. doi:10.3945/ajcn.2008.26594, by Looker AC, Pfeiffer CM, Lacher DA, Schleicher RL, Picciano MF, Yetley EA. National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, Maryland; National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia; Office of Dietary Supplements, National Institutes of Health, Bethesda, Maryland, USA. [E-mail: AC Looker firstname.lastname@example.org]