Calcium and vitamin D, whether from food or supplements, may help lower the risk of developing type 2 diabetes, according to a research review.

A number of studies have found links between type 2 diabetes risk and calcium, vitamin D and dairy food intake. When the results from these studies are combined, the new review found, people with the highest intakes of vitamin D and calcium had an 18 percent lower risk of diabetes than those with the lowest intakes.

Similarly, people who ate the most dairy food had a 14 percent lower diabetes risk than those who ate the least dairy.

Though it's not clear why calcium and vitamin D are linked to diabetes risk, lab research has pointed to some possibilities, according to the review authors, led by Dr. Anastassios G. Pittas of Tufts-New England Medical Center in Boston.

Both nutrients may be important in the functioning of insulin-producing cells in the pancreas, and in the body's proper use of insulin, the researchers explain in their report, published in the Journal of Clinical Endocrinology & Metabolism.

Insulin is a hormone that helps move sugar from the blood into the body's cells to be used for energy; type 2 diabetes develops when the body becomes resistant to insulin, allowing blood sugar levels to soar.

Only a limited number of studies have tested whether calcium or vitamin D supplements can improve the body's insulin sensitivity and blood sugar metabolism. And the studies that have been done have reached conflicting conclusions, the review found.

A few trials have, however, suggested that the supplements may forestall type 2 diabetes in people who are on the verge of developing diabetes, or "pre-diabetic," based on their blood sugar levels, according to Pittas and his colleagues.

It's too soon to recommend calcium or vitamin D for managing diabetes, the researchers conclude, but more clinical trials are warranted.

Many Americans do not get enough vitamin D or calcium, they note, and supplementing people's diets with the nutrients would be an easy, inexpensive way to prevent or treat type 2 diabetes.