Objective: The purpose of this study was to prospectively examine the association between vitamin D and calcium intake and risk of type 2 diabetes.
Research design and methods: In the Nurses' Health Study, we followed 83,779 women who had no history of diabetes, cardiovascular disease, or cancer at baseline for the development of type 2 diabetes. Vitamin D and calcium intake from diet and supplements was assessed every 2-4 years. During 20 years of follow-up, we documented 4,843 incident cases of type 2 diabetes.
Results: After adjusting for multiple potential confounders, there was no association between total vitamin D intake and type 2 diabetes. However, the relative risk (RR) of type 2 diabetes was 0.87 (95% CI 0.75-1.00; P for trend = 0.04) comparing the highest with the lowest category of vitamin D intake from supplements. The multivariate RRs of type 2 diabetes were 0.79 (0.70-0.90; P for trend <0.001) comparing the highest with the lowest category of calcium intake from all sources and 0.82 (0.72-0.92; P for trend <0.001) comparing the highest with the lowest category of calcium intake from supplements. A combined daily intake of >1,200 mg calcium and >800 IU vitamin D was associated with a 33% lower risk of type 2 diabetes with RR of 0.67 (0.49-0.90) compared with an intake of <600 mg and 400 IU calcium and vitamin D, respectively.
Conclusions: The results of this large prospective study suggest a potential beneficial role for both vitamin D and calcium intake in reducing the risk of type 2 diabetes.