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NEW YORK (Reuters Health) - 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, told Reuters Health in an email.
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, told Reuters Health.
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.
SOURCE: bit.ly/qauWcN American Journal of Clinical Nutrition, online June 29, 2011