Low vitamin D levels have been linked to increased risk of diabetes, heart disease, and cancer. But will taking a D supplement lower your risk? Nutrition Diva reviews the latest research.
Q. "I was recently diagnosed with pre-diabetes. The doctor prescribed metformin as well as vitamin D3. I thought that was kind of funny but he described a recent study that showed that the great majority of patients suffering from diabetes, heart problems, and cancer are vitamin D3 deficient. He thinks this deficiency may be causing my rise in sugar levels. What is vitamin D3 and how is it different from regular vitamin D found in milk?"
A. Vitamin D3 (cholecalciferol) is the form of vitamin D that your skin makes when it is exposed to sunlight or ultraviolet light. Vitamin D2 (ergocalciferol) is the form that's commonly used to fortify milk. In the past, vitamin D supplements almost always provided D2. Since D3 is now understood to be the more active form, supplements are more likely to contain D3 these days. The best dietary sources of vitamin D are cod liver oil, oily fish, liver, egg yolks, mushrooms, and fortified dairy products.
See also: What are the Benefits of Vitamin D?
But what does any of that have to do with diabetes, you might ask? Over the last decade or so, studies have linked low vitamin D levels to an increasing number of common diseases, everything from cancer to multiple sclerosis. This led to the hypothesis that D deficiency might be causing these diseases - which offered the tantalizing hope that giving people vitamin D supplements would lower the risk of these diseases.
We've now had a while to test this hypothesis and some of the results have been pretty disappointing. Contrary to a lot of hopes and expectations (not least among those who sell supplements), giving people more vitamin D has not been shown to make a difference in rates of cancer or cardiovascular disease.
See also: Understanding Vitamin D Deficiency
It could be that these diseases cause low vitamin D levels, rather than the other way around. Or maybe vitamin D was a red herring. People with low vitamin D tend to be people who don't get a lot of exposure to natural sunlight. Maybe there's something else about sunlight that lowers disease risk.
Vitamin D Improves Blood Sugar and Insulin
Diabetes is the one bright spot in this picture. Preliminary studies suggest that vitamin D supplements may actually improve blood sugar and insulin levels in diabetics, especially those who are vitamin D deficient.
You don't say whether your doctor tested your vitamin D levels before prescribing the supplements. He may not have felt it was necessary. Low levels are pretty common and vitamin D is pretty safe and well-tolerated.
See also: How Much Vitamin D Is Safe?
At this point, it's really a "might help, probably can't hurt" sort of therapy. But if you wanted to hedge your bets, you might also want to try to get a little more sunshine into your life!
Check out my episode on Reversing Diabetes with Diet for more tips on how to control diabetes without medication.