Over the past decade, a low level of vitamin D in the blood has emerged as a possible risk factor for type 2 diabetes, and vitamin D supplementation has been proposed as a potential intervention to lower diabetes risk.
But if you have pre-diabetes -- meaning you have factors that put you at risk for developing diabetes -- taking excessive amounts of vitamin D to prevent diabetes won't help, says a recent major study published recently in the New England Journal of Medicine.
Cyrus Desouza, M.B.B.S., professor in UNMC Department of Internal Medicine's Division of Diabetes, Endocrinology and Metabolism, co-authored an article about the five-year clinical research study. He directed the UNMC and Omaha VA Medical Center clinical study site to evaluate whether larger than standard doses of vitamin D prevent progression from pre-diabetes to diabetes.
More than 84 million adults in the United States have an increased risk of type 2 diabetes based on a fasting glucose or glycated hemoglobin level above the normal range but below the threshold for diabetes.
"Billions of dollars are being spent on vitamin D. Preliminary studies had showed benefit in preventing diabetes," said Dr. Desouza said. "Vitamin D may be necessary to prevent diabetes, if you have low levels of vitamin D, but not if you have normal levels of vitamin D. Taking excessive amounts is not helpful. It can sometimes be harmful."
The clinical research study, led by Tufts Medical Center in Boston by Anastassios Pittas, M.D., evaluated the safety and effectiveness of oral administration of 4,000 IUs of vitamin D3 per day for diabetes prevention in adults at high risk for type 2 diabetes.
Of 2,423 study participants, 1,211 took vitamin D and 1,212 took placebo. A total of 170 study participants were recruited from UNMC and the Omaha VA Hospital. At the end of the study, which took place at 22 sites, diabetes occurred in 293 participants in the vitamin D group and 323 in the placebo group.
Dr. Desouza advises patients who don't want to get type 2 diabetes to concentrate on lifestyle changes such as diet and exercise.
"Lose weight if you're overweight and watch what you eat. That's the only effective way to prevent diabetes -- it's been proven in many research studies," Dr. Desouza said.
The study was funded primarily by the National Institute of Diabetes and Digestive and Kidney Diseases, the Office of Dietary Supplements of the National Institutes of Health and the American Diabetes Association.