Vitamin D may reduce the chances of type 2 diabetes, doctors said. In one review of 19 studies, people who got more than 500 IU of vitamin D per day were 13 percent less likely to develop type 2 diabetes compared to those who got less than 200 IU per day. People with the highest blood levels of vitamin D—more than 25 nanograms per milliliter of blood (ng/mL)—were 43 percent less likely to develop type 2 diabetes compared to those with levels below 14 ng/mL.
In two studies, people with insulin resistance—where the body does not efficiently use insulin to metabolize blood sugar—insulin sensitivity increased as vitamin D levels rose. Doctors believe the optimal range for vitamin D blood levels is between 20 and 60 ng/mL, and measurement tests are now readily available.