Serum 25-hydroxyvitamin D, diabetes, and ethnicity in the Third National Health and Nutrition Examination Survey.

OBJECTIVE To determine the association between serum 25-hydroxyvitamin D (25OHD) and diabetes risk and whether it varies by ethnicity. RESEARCH DESIGN AND METHODS We performed an analysis of data from participants who attended the morning examination of the Third National Health and Nutrition Examination Survey (1988-1994), a cross-sectional survey of a nationally representative sample of the U.S. population. Serum levels of 25OHD, which reflect vitamin D status, were available from 6,228 people (2,766 non-Hispanic whites, 1,736 non-Hispanic blacks, and 1,726 Mexican Americans) aged > or =20 years with fasting and/or 2-h plasma glucose and serum insulin measurements. RESULTS Adjusting for sex, age, BMI, leisure activity, and quarter of year, ethnicity-specific odds ratios (ORs) for diabetes (fasting glucose > or =7.0 mmol/l) varied inversely across quartiles of 25OHD in a dose-dependent pattern (OR 0.25 [95% CI 0.11-0.60] for non-Hispanic whites and 0.17 [0.08-0.37] for Mexican Americans) in the highest vitamin D quartile (25OHD > or =81.0 nmol/l) compared with the lowest 25OHD (< or =43.9 nmol/l). This inverse association was not observed in non-Hispanic blacks. Homeostasis model assessment of insulin resistance (log e) was inversely associated with serum 25OHD in Mexican Americans (P=0.0024) and non-Hispanic whites (P=0.058) but not non-Hispanic blacks (P=0.93), adjusting for confounders. CONCLUSIONS These results show an inverse association between vitamin D status and diabetes, possibly involving insulin resistance, in non-Hispanic whites and Mexican Americans. The lack of an inverse association in non-Hispanic blacks may reflect decreased sensitivity to vitamin D and/or related hormones such as the parathyroid hormone.