Vitamin D and type 2 diabetes mellitus: where do we stand?

In-vitro and observational studies have established a link between vitamin D deficiency and different type 2 diabetes outcomes (insulin resistance, insulin secretion, glucose intolerance). Although the number of randomized controlled trials vs placebo is small, vitamin D (VTD) has been shown to prevent increases in glucose concentration and insulin resistance, enhance insulin sensitivity and reduce systolic blood pressure in type 2 diabetic patients.

In this review, we have focused on the potential mechanisms that might explain the association between VTD and type 2 diabetes mellitus (T2DM). We have also evaluated the different epidemiological and observational studies on the topic, as well as the various interventional studies.

Although the in vitro studies appear to be promising in explaining the link between VTD metabolism and T2DM, the results of in vivo studies are conflicting. This could be related to differences in their methodological approaches.

Although more studies are needed to confirm the role of VTD in the treatment of T2DM, there is nevertheless enough evidence at this time to suggest a need to maintain 25-OH vitamin D levels in T2DM patients around 30 ng/mL over the course of a year.