Plasma 25-hydroxyvitamin D concentration and risk of type 2 diabetes and pre-diabetes: 12-year cohort study

BackgroundIt has been reported that higher plasma 25-hydroxyvitamin D is associated with lower risk of type 2 diabetes. However the results to date have been mixed and no adequate data based on a cohort are available for the high end of the normal range, above approximately 32 ng/ml or 80 nmol/L.MethodsWe performed a cohort study of 903 adults who were known to be free of diabetes or pre-diabetes during a 1997–1999 visit to a NIH Lipid Research Centers clinic. Plasma 25(OH)D was measured at Visit 8 in 1977–1979. The mean age was 74 years. The visit also included fasting plasma glucose and oral glucose tolerance testing.Follow-up continued through 2009.ResultsThere were 47 cases of diabetes and 337 cases of pre-diabetes. Higher 25(OH)D concentrations (> 30 ng/ml) were associated with lower hazard ratios (HR) for diabetes: 30–39 ng/ml or 75–98 nmol/L: HR = 0.31, 95% CI = 0.14–0.70; for 40–49 ng/ml or 100–122 nmol/L: HR = 0.29, CI = 0.12–0.68; for > 50 ng/ml or 125 nmol/L: HR = 0.19, CI = 0.06–0.56. All HRs are compared to p for trend of 0.005. Each 10 ng/mL or 25 nmol/L higher 25(OH)D concentration was associated with a HR of 0.64, CI = 0.48–0.86. 25(OH)D concentrations were more weakly inversely associated with pre-diabetes risk, and the trend was not significant.ConclusionFurther research is needed on whether high 25(OH)D might prevent type 2 diabetes or transition of prediabetes to diabetes.