While observational studies have suggested that low blood levels of vitamin D are associated with higher risk of developing type 2 diabetes, a clinical trial recently published in The American Journal of Clinical Nutrition found that supplementation with vitamin D3 had no effect on insulin action in people with prediabetes. Sixty-four participants with prediabetes received 3,000 IU of vitamin D3 or a placebo daily for 26 weeks. While the blood levels of vitamin D (25-hydroxyvitamin D) rose significantly in the vitamin D3 group compared to the placebo group, confirming that subjects were taking the supplements, there was no difference in any measure of glycemic control or pancreatic cell function between groups at the end of the study period.
Improving blood sugar control in people with prediabetes can prevent the conversion to type 2 diabetes. Weight loss, a healthy dietary pattern, and physical activity are not as easy as popping a vitamin pill, but they are certainly more effective.