Reviewing Role of Vitamin D in Endocrine Disorders

It may be time for endocrinologists to rethink vitamin D levels in their patients, according to some experts. With research challenging the recommended daily intake of vitamin D as well as studies on the role vitamin D plays in inflammation and disease prevention, clinicians have a great deal to consider.

In a study published in the journal Cell Reports, for instance, researchers report that inactivation of the vitamin D receptor induced diabetes and atherosclerosis in animal models.¹

Researchers found that inactivating the vitamin D receptor on monocytes and macrophages promoted inflammation of the liver and in artery walls. It also increased the ability of monocytes in the blood to adhere and migrate into blood vessel walls.

“We found a novel factor in that the monocytes carry the cholesterol into the plaque and that is what is leading to atherosclerosis,” said senior study investigator Carlos Bernal-Mizrachi, MD, who is an associate professor of medicine and of cell biology and physiology at Washington University School of Medicine in St. Louis, Missouri.

He said inadequate vitamin D turned immune cells into transporters of fat. Bernal-Mizrachi, who is also an endocrinologist, said this may help pave the way for a better understanding of how diabetes and atherosclerosis are linked and provide new possibilities for therapy. 

It is well established that LDL cholesterol carries fat deposits to vessel walls. Now this study suggests that when monocytes don’t have enough vitamin D, they can do it, too.

“The findings are important for endocrinologists because we don’t just treat diabetes; we also treat heart disease. And as endocrinologists, we have to work to try to find out the role of vitamin D,” Bernal-Mizrachi said in an interview with Endocrinology Advisor.

Vitamin D and Inflammation

For years, researchers have been studying vitamin D’s possible roles in inflammation and inflammatory diseases, such as type 2 diabetes and atherosclerosis.

Co-study investigator Amy Riek, MD, who is an assistant professor of medicine at Washington University, said it was known that when monocytes matured and became macrophages, they would eat cholesterol deposited inside the blood vessel wall, according to a press release.

However, in these experiments when the monocytes didn’t have vitamin D, they were still in circulation absorbing cholesterol and carrying it in the bloodstream. This is an important discovery, Riek said, because it is much easier to find treatments that target something in the blood as opposed to targeting the same cells after they move into the wall of a blood vessel.

In the study, the researchers found the problem was reversible in the mice. When the animals that had developed type 2 diabetes and atherosclerosis received bone marrow transplants from mice with healthy vitamin D receptors on their monocytes and macrophages, their inflammation levels decreased, and the animals had lower blood glucose and became more sensitive to insulin.

Currently, Bernal-Mizrachi and Riek are conducting clinical studies in patients with type 2 diabetes, treating them with vitamin D to see whether it can prevent some of the complications of diabetes and inflammation. As part of their study, they are isolating monocytes from the blood of patients before and after vitamin D therapy.