There is increasing evidence that vitamin D influences many non-skeletal medical conditions, including heart disease, cancer, certain autoimmune diseases and type 2 diabetes. Observational research has shown that seasonal variation in blood sugar control in the winter may be partly due to vitamin D, since levels are generally much lower in the winter.
In a study published in the European Journal of Clinical Nutrition, researchers examined the association between vitamin D status and the incidence of Type 2 diabetes. After a thorough review of the literature, 8 observational studies and 11 randomly controlled trials were included in the review. When compared to those with a vitamin D intake of <200 IU/day, intake of >500 IU/day decreased the risk of type 2 diabetes by 13%. Compared to those with the lowest serum vitamin D levels (<14 ng/ml or 35 mmol/L), adults with the highest vitamin D status (>25 ng/ml or 62.5 mmol/L) had a 43% lower risk of developing type 2 diabetes. In two trials that included patients with glucose intolerance, vitamin D supplementation improved measures of insulin resistance. No significant effect of vitamin D on glycemic outcomes was evident in the trials that included subjects with normal glucose tolerance at baseline.
The results of this review show that vitamin D may play a role in the development of type 2 diabetes, although high-quality studies are still needed to determine a potential mechanism between vitamin D concentration and relevant glycemic outcomes.
SOURCE J Mitri, M D Muraru and A G Pittas. Vitamin D and type 2 diabetes: a systematic review. European Journal of Clinical Nutrition (2011) 65, 1005–1015.