While the benefits of vitamin D in promoting bone health are well known, there is evidence from Brazil showing that vitamin D may promote greater insulin sensitivity, thus lowering glucose levels and the risk of developing type 2 diabetes. Results are published online in Menopause, the journal of The North American Menopause Society (NAMS).
Other recent studies have shown a clear relationship between vitamin D and glycemic control, 
suggesting that vitamin D increases insulin sensitivity and improves pancreatic beta-cell function. In this was a cross-sectional study involving 680 Brazilian women, 35 to 74 years of age, selected through systematic sampling. Each participant, fasting blood samples were collected for the determination of 25(OH)D and glucose levels.
Among the participants, 176 women self identified as having diabetes, 92 women took at least one hypoglycemic medication and 30 used insulin. One woman had serum 25(OH)D level of 96.5 ng/mL, and therefore was excluded from the study. Of the women interviewed, 24 (3.5%) reported using vitamin D supplements. The study authors reported the following results:
- Vitamin D supplementation was found to be negatively associated with high glucose levels.
- Habitual exposure to the sun also provided the same association, demonstrating that vitamin D deficiencies are associated with high blood glucose levels.
- The mean fasting blood glucose level was 105 mg/dL (range 26-401 mg/dL).
- Fasting serum levels of 25(OH)D were <30 ng/mL in 65.4% of the participants and <20 ng/mL in 25.6%.
- Serum 25(OH)D level <30 ng/mL was positively associated with a blood glucose level ≥100 mg/dL (odds ratio [OR] 1.29, 95% confidence interval [CI] 1.05-1.57), as was a serum 25(OH)D level <20 ng/mL (OR 1.25, 95% CI 1.04-1.50).
- A glucose level of ≥100 mg/dL was also significantly tied to obesity, hypertension, and older age among women:
- BMI ≥30: OR 1.42 (95% CI 1.19-1.69, P<0.001)
- SBP ≥130 or DBP ≥85 mmHg: OR 1.27 (95% CI 1.03-1.56, P=0.025)
- Ages >60: OR 1.33 (95% CI 1.11-1.61, P=0.003)
“Although a causal relationship has not been proven, low levels of vitamin D may play a significant role in type 2 diabetes mellitus,” says Dr. JoAnn Pinkerton, NAMS executive director. “Vitamin D supplementation may help improve blood sugar control, but intervention studies are still needed.”
The authors noted: “evidence from the literature which suggested that vitamin D plays a role in pancreatic beta cell function, improving the insulin response to an increase in the blood glucose level.” There is now evidence that a higher serum level of 25-hydroxyvitamin D (25[OH]D) is associated with a lower risk of developing type 2 diabetes mellitus, because it provides better glycemic control, possibly by promoting greater insulin sensitivity, and also by improving pancreatic beta cell function.
