Association of racial disparities in the prevalence of insulin resistance with racial disparities in vitamin D levels: National Health and Nutrition Examination Survey (2001-2006)

Abstract

We tested the hypothesis that racial differences in vitamin D levels are associated with racial disparities in insulin resistance between blacks and whites. Among 3628 non-Hispanic black and white adults in the National Health and Nutrition Examination Survey from 2001 to 2006, we examined the association between race and insulin resistance using the homeostasis assessment model for insulin resistance. We conducted analyses with and without serum 25-hydroxyvitamin D (25[OH]D). We adjusted for age, sex, educational level, body mass index, waist circumference, physical activity, alcohol intake, smoking, estimated glomerular filtration rate, and urinary albumin/creatinine ratio. Blacks had a lower mean serum 25(OH)D level compared with whites (14.6 [0.3] ng/mL vs 25.6 [0.4] ng/mL, respectively; P < .0001). Blacks had a higher odds ratio (OR) for insulin resistance without controlling for serum 25(OH)D levels (OR, 1.67; 95% confidence interval, 1.26-2.20). The association was not significant (OR, 1.28; 95% confidence interval, 0.90-1.82) after accounting for serum 25(OH)D levels. The higher burden of insulin resistance in blacks compared with whites may be partially mediated by the disparity in serum 25(OH)D levels.

Fig. 1

Prevalence of study participants (percent) in each quintile of serum 25[OH] D stratified by race/ethnicity. Serum 25[OH] D levels were grouped into quintiles based on the entire sample distribution. For serum 25[OH] D levels, the 1^st quintile was < 15.7 ng/ml; 2^nd quintile was 15.7 ng/ml to < 20.7 ng/ml; 3^rd quintile was 20.7 ng/ml to < 25.1 ng/ml; 4^th quintile was 25.1 ng/ml to < 31.0 ng/ml; and the 5^th quintile was > 31.0 ng/ml.