Vitamin D prevents diabetes and clogged arteries in mice

In recent years, a deficiency of vitamin D has been linked to type 2 diabetes and heart disease, two illnesses that commonly occur together and are the most common cause of illness and death in Western countries. Both disorders are rooted in chronic inflammation, which leads to insulin resistance and the buildup of artery-clogging plaque.

Now, new research in mice at Washington University School of Medicine in St. Louis suggests vitamin D plays a major role in preventing the inflammation that leads to type 2 diabetes and atherosclerosis. Further, the way key immune cells behave without adequate vitamin D may provide scientists with new therapeutic targets for patients with those disorders.

The study appears March 19 in the journal Cell Reports.

Studying mice that lacked the ability to process vitamin D in immune cells involved in inflammation, the researchers found that the animals made excess glucose, became resistant to insulin action and accumulated plaques in their blood vessels.

"The finding that vitamin D helps regulate glucose metabolism may explain previous epidemiological studies identifying an increased risk of diabetes in patients with vitamin D deficiency," said senior investigator Carlos Bernal-Mizrachi, MD, associate professor of medicine and of cell biology and physiology. "In our study, inactivation of the vitamin D receptor induced diabetes and atherosclerosis, so normalizing vitamin D levels may have the opposite effect."

In addition, he said inadequate vitamin D turned immune cells into transporters of fat. That may help researchers better understand how diabetes and atherosclerosis are linked and provide new possibilities for therapy.

For years, researchers have been studying vitamin D's possible roles in inflammation and inflammatory diseases, such as type 2 diabetes and atherosclerosis. By engineering mice without the vitamin D receptor on important immune cells called monocytes and macrophages, the researchers were able to learn how those conditions are linked, according to Bernal-Mizrachi.

Monocytes are white blood cells made in the bone marrow that circulate in the bloodstream. After a few days, they typically move into the body's tissues where they mature into cells called macrophages.

"Inactivating the vitamin D receptor on monocytes and macrophages promotes inflammation of the liver and in artery walls," he said. "It also increases the ability of monocytes in the blood to adhere and migrate into blood vessel walls, where they deposit cholesterol and secrete inflammatory substances that lead to diabetes and heart disease."

He said the findings suggest that getting enough vitamin D may reduce those properties in immune cells, decreasing inflammation and reducing the onset of a combination of heart disease and diabetes, which is often referred to as cardiometabolic disease. In addition, the researchers found that without vitamin D, monocytes carried fat to the walls of blood vessels, which is something that hadn't been observed previously.