92 adults were randomly assigned in a 2-by-2 factorial-design, double-blinded, placebo-controlled trial to receive either D3 (2000 IU once daily) or calcium carbonate (400 mg twice daily) for 16 weeks. Participants had a mean age of 57 y, a body mass index (BMI) of 32, and glycated hemoglobin (Hb A1c) of 5.9%.
Results showed that the vitamin D3 group had improvements in insulin secretion, and Hb A1c did not increase significantly (compared to the non-vitamin D3 group). There was no significant effect of calcium in any of the outcomes measured.
About two weeks ago, I had discussed another study (a meta-analysis) that confirmed vitamin D3's ability to reduce the risk of type 2 diabetes.
So the take home message is, if you're at risk of diabetes (and who isn't?) or have diabetes (type 2, but I believe type 1 as well, since an improvement in beta-cell function would help), you should be taking vitamin D3. As I mentioned in other posts on vitamin D, most experts are suggesting 5000 IU daily is what's needed. Yes, this is a relatively high dose if you're stuck in the old ways of thinking about vitamin D. Not so high if you're aware of the newer research on vitamin D in the last few years.
Source: Effects of vitamin D and calcium supplementation on pancreatic β cell function, insulin sensitivity, and glycemia in adults at high risk of diabetes: the Calcium and Vitamin D for Diabetes Mellitus (CaDDM) randomized controlled trial
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