Vit D in US  1988 to 2004
Serum 25-hydroxyvitamin D status of the US population: 1988–1994 compared with 2000–20041,2,3
Anne C Looker, Christine M Pfeiffer, David A Lacher, Rosemary L Schleicher, Mary Frances Picciano and Elizabeth A Yetley
American Journal of Clinical Nutrition, doi:10.3945/ajcn.2008.26182
Vol. 88, No. 6, 1519-1527, December 2008
1 From the National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD (ACL and DAL); the National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA (CMP and RLS); and the Office of Dietary Supplements, National Institutes of Health, Bethesda, MD (MFP and EAY)
See corresponding editorial on page 1455.

2 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.

3 Reprints not available. Address correspondence to AC Looker, Room 4310, National Center for Health Statistics, 3311 Belcrest Road, Hyattsville, MD 20782. E-mail: acl1@cdc.gov.

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 {approx}10 nmol/L, and adjustment for changes in the factors likely related to real changes in vitamin D status (ie, BMI, 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.