Vitamin D May Help Prevent Diabetes

Low levels of vitamin D and calcium in the body appear to be associated with type 2 diabetes.  There is no evidence from clinical trials, however, to support this impression. This study focused on the effect of vitamin D and calcium supplementation, taken together or alone, on type 2 diabetes in adults. It found that vitamin D, with or without calcium, can help in delaying the onset of type 2 diabetes in individuals who have a high risk of developing the disease.

Insulin is a hormone that plays a key role in regulating the uptake of blood sugar by cells. Lack of insulin or faulty insulin function results in a rise in blood sugar, leading to diabetes. Insulin is produced in pancreatic β-cells. Type 1 diabetes results when β-cells cannot produce enough insulin. Type 2 diabetes results when cells do not respond well to insulin, a condition called insulin resistance. The authors evaluated the role of vitamin D and calcium in the prevention of diabetes in high-risk individuals. The effects of vitamin D and calcium supplementation on the function of pancreatic β-cells, tolerance to glucose, and sensitivity to insulin were evaluated in clinical trials.

* Participants who were at a high risk of diabetes were identified through medical tests. All participants lived in the Boston metropolitan area.
* Ninety-two participants were selected and they were divided into four groups. The first group received vitamin D alone, the second received a placebo, the third received both vitamin D and calcium, and the fourth received calcium alone. Neither the participant nor the provider knew which treatment the participant received.
* A test measuring the function of insulin-producing cells was carried out five times during the 16-week period.
* Blood tests indicated blood sugar levels.

* Improved β-cell function, insulin secretion, and increased sensitivity to insulin appeared to improve in those who received vitamin D supplementation with or without calcium. These properties appeared to get worse in those who did not receive vitamin D supplements.
* Insulin secretion increased the most in those who received both vitamin D and calcium.
* Blood glucose levels increased less in the vitamin D group.

Next steps/shortcomings
Most of the participants in this study were white. People from different races should be considered for a more generalizable study on the effect of vitamin D and calcium on diabetes risk. In addition, participants from different geographical regions should be evaluated in future studies to obtain a reliable conclusion on the effects of vitamin D.

In this study, the authors propose vitamin D supplementation for adults who have a high risk of developing type 2 diabetes. By using a highly sensitive measure of β-cell function, this study showed that vitamin D helps to improve pancreatic β-cell function and insulin secretion. This can lead to lowered blood glucose levels, which in turn can prevent the progression of diabetes in people at high risk. Since the clinical trial for this study was carried out for a short term, it cannot be held accountable for the safety and long-term effects of vitamin D supplementation. The study should be extended to long-term clinical trials to establish the safety of such treatment.

For More Information:
Effects of Vitamin D and Calcium Supplementation on the Function of Insulin-producing Cells, Insulin Sensitivity, and Blood Glucose Levels in Adults at High Risk of Diabetes
Publication Journal: American Journal of Clinical Nutrition, June 2011
By Joanna Mitri; Bess Dawson-Hughes, et al. The Tufts Medical Center, Boston, Massachusetts

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