New York: Vitamin D supplements reduced risk factors for type 2 diabetes by improving the function of insulin-producing cells in pre-diabetic volunteers, a new study has found.
"The results...suggest that vitamin D supplementation may help to improve the main defect in type 2 diabetes," co-author Dr. Anastassios Pittas, an endocrinologist at Tufts University Medical Center in Boston, said.
Type 2 diabetes, the most common form of the disease, affects millions of Americans. The condition is characterized by high blood-sugar levels resulting from the body`s poor response to insulin, a chemical that removes sugar from the bloodstream and stores it in the liver and muscles. Insulin is made by beta cells in the pancreas.
To see whether taking vitamin D would improve people`s ability to handle blood sugar, researchers gave 92 pre-diabetic adults either vitamin D3 supplements, calcium supplements, both, or placebos. After four months, the participants` blood was tested for several known diabetes risk factors.
The measures included hemoglobin A1C, an indicator of blood-sugar levels over time, and beta-cell function, as reflected by how much insulin is being released and how well the body responds to it.
At the outset, participants were considered pre-diabetic if they were overweight and had blood-sugar levels that were above normal but not high enough to be classified as diabetic.
The researchers found that vitamin D significantly increased the beta-cell function of pre-diabetic adults, according to results published in the American Journal of Clinical Nutrition. The vitamin D group also had slightly more favorable hemoglobin A1C levels.
Calcium had no effect on beta-cell function, either alone or in combination with vitamin D.
The results don`t necessarily indicate that vitamin D will reduce the likelihood of diabetes, since the study just measures blood test results. However, the important finding is that "supplementation affects biology," Dr. Ian De Boer, a nephrologist at the University of Washington in Seattle who was not involved in the study said.
De Boer estimated that in the study vitamin D improved beta-cell function between 15 and 30 percent.
Previous research has explored the connection between vitamin D and diabetes, with mixed results. Several studies have shown that people with low levels of vitamin D may be at a higher risk for diabetes, but most have been unable to demonstrate that vitamin D supplementation can help prevent diabetes.
One recent study from Iran did show that vitamin D could help control blood sugar, which in itself may stave off diabetes.
"These findings are interesting but preliminary," cautioned Dr. Susan Kirkman of the American Diabetes Association.
"Vitamin D may have a role in delaying the progression to clinical diabetes in adults at high risk of Type 2 diabetes," wrote the authors of the new study, but they agree that role has not been adequately demonstrated.
"At this point, I would not recommend vitamin D based on the results of our study for prevention of diabetes," Pittas said. However, with larger and longer studies of vitamin D`s connection to diabetes currently underway, he said, a more definitive answer could be forthcoming.