Vitamin D and incidence of diabetes: a prospective cohort study

To investigate the relationship between levels of 25-hydroxyvitamin D and the incidence of type 2 diabetes in a Spanish population.

We undertook a population-based prospective study in a population from southern Spain. The first phase of the study (1996-1998) included 1226 individuals. Of this original cohort, 988 persons were reassessed in 2002-2004 and 961 in 2005-2007. Measurements were made of 25-hydroxyvitamin D and intact parathyroid hormone in 2002-2004 and an oral glucose tolerance test was done in three time points.

The incidence of diabetes in subjects with 25-hydroxyvitamin D levels ≤ 18.5 ng/mL (percentile 25) was 12.4% vs 4.7% in subjects with levels >18.5 ng/mL. The likelihood of having diabetes during the four years of follow-up was significantly lower in the subjects with higher levels of 25-hydroxyvitamin D [OR = 0.17 (0.05-0.61)]. None of the subjects with levels higher than 30 ng/mL developed diabetes.

In this prospective study, we found a significant inverse association between serum 25-hydroxyvitamin D levels and the risk for type 2 diabetes in a population from the south of Spain.