25-Hydroxyvitamin D deficiency is associated with fatal stroke among whites but not blacks: The NHANES-III linked mortality files

Objective: Deficient 25-hydroxyvitamin D (25[OH]D) levels are associated with cardiovascular disease (CVD) events and mortality. 25(OH)D deficiency and stroke are more prevalent in blacks. We examined whether low 25(OH)D contributes to the excess risk of fatal stroke in blacks compared with whites. Methods: The Third National Health and Nutrition Examination Survey, a probability sample of U.S. civilians, measured 25(OH)D levels and CVD risk factors from 1988 through 1994. Vital status through December 2006 was obtained by a linkage with the National Death Index. In white and black adults without CVD reported at baseline (n = 7981), Cox regression models were fit to estimate hazard ratios (HR) for fatal stroke by 25(OH)D status and race. Results: During a median of 14.1 y, there were 116 and 60 fatal strokes in whites and blacks, respectively. The risk of fatal stroke was greater in blacks compared with whites in models adjusted for socioeconomic status and CVD risk factors (HR 1.60, 95% confidence interval 1.01-2.53). Mean baseline 25(OH)D levels were significantly lower in blacks compared with whites (19.4 versus 30.8 ng/mL, respectively). In multivariable-adjusted models, deficient 25(OH)D levels lower than 15 ng/mL were associated with fatal stroke in whites (HR 2.13, 1.01-4.50) but not blacks (HR 0.93, 0.49-1.80). Conclusions: Vitamin D deficiency was associated with an increased risk of stroke death in whites but not in blacks. Although blacks had a higher rate of fatal stroke compared with whites, the low 25(OH)D levels in blacks were unrelated to stroke incidence. Therefore 25(OH)D levels did not explain this excess risk.