High doses of the supplement—up to 10 times the recommended daily allowance—help the body regain its capacity to process glucose, or blood sugar. Diabetics have become insulin resistant, and, as a result, can't break down glucose properly.
But after taking the supplement for six months, glucose metabolism was starting to improve, say researchers from Laval University in Quebec. It had a positive effect even among diabetics whose vitamin D levels were normal.
The researchers tested glucose metabolism in a group of diabetics and prediabetics before and after they were given the supplements. After six months, tests showed that the supplements had "significantly improved" the ability of insulin to break down glucose.