Influence of obesity on vitamin D-binding protein and 25-hydroxy vitamin D levels in African American and white women.

25-Hydroxy vitamin D (25OHD) is lipophilic and highly bound to vitamin D-binding protein (VDBP) in plasma. In the present study, we examined VDBP and 25OHD levels by race and body mass index (BMI) in young adult women to determine whether circulating VDBP plays a role in the low levels of 25OHD with obesity and among African Americans. In agreement with previous studies, mean 25OHD levels were lower in African American women than in whites (P < .01). In a hierarchical multiple regression model, BMI was associated with 25OHD after adjustment for age in white women (P = .02, R(2) = .10) but not in African American women. The VDBP levels, by contrast, were similar in African Americans and whites, and were unrelated to BMI in either racial group. Furthermore, VDBP was unrelated to the plasma level of 25OHD. These data confirm an interaction between race and obesity in vitamin D metabolism, and imply that the carrier protein is not an important determinant of circulating 25OHD in women, nor is it affected by race or adiposity.