Vitamin D has long been known to be critical for calcium metabolism and research has shown that deficiency of this fat soluble vitamin has been linked to a variety of diseases ranging from cancer to cardiovascular disease and Type 2 Diabetes (T2D). Although underlying mechanisms are still not completely understood, it’s thought that the association of low serum levels of vitamin D with T2D may be mediated by a direct effect of vitamin D on β-cell function, and thus insulin secretion. Studies have indicated that vitamin D deficiency is linked to insulin resistance and associated with markers of impaired glucose metabolism such as HbA1c.
In this systematic review and meta-analysis of 24 randomized clinical trials (RCTs), researchers wanted to assess if supplementation with vitamin D affected glycemic control in patients with T2D. They found that supplementation with vitamin D was associated with lower HbA1c levels but not lower fasting blood glucose (FBG). However in a subgroup analysis of patients with vitamin D at baseline (or at study entry), supplementation was associated with both reducing HbA1c and FBG levels. A second subgroup analysis on patients with BMI < 30, also showed statistically significant reductions in HbA1c levels with vitamin D supplementation.
Why is this clinically relevant?
- Vitamin D is crucial for more than calcium metabolism and deficiency may be linked to various health conditions
- Low levels of vitamin D may be linked to impaired glucose metabolism
- Results from this study suggest that supplementation with vitamin D may be useful for improving glycemic control in T2D patients, particularly those with underlying vitamin D deficiency and also individuals who are not obese
 Dalgard C, Petersen MS, Weihe, P et al. Diabetes Care. 2011 Jun;34(6):1284-8