In a recent study of the relationship between vitamin D deficiency and glucose intolerance in people with type 2 diabetes, more than 90% of the type 2 diabetes patients were found to be deficient in vitamin D, with their control over the disease worsening as their deficiency increased.
The study team, led by Esther Krug, MD, an endocrinologist at Sinai Hospital of Baltimore and assistant professor of medicine at Johns Hopkins University School of Medicine, looked at the medical charts of 124 people with type 2, tracking their numbers over a five-year span, from 2003 to 2008. In addition to such data as age, ethnicity, family history of diabetes, and A1c numbers, the charts recorded vitamin D levels.
The researchers divided the patients into four groups based on their levels of vitamin D: normal (32 nanograms of the vitamin per deciliter of blood); mildly deficient; moderately deficient; and severely deficient. They found that only 8.9% of the patients could be classified as normal. The remaining 91.1% were described as vitamin D deficient-35.5% severely, 38.7% moderately, and 16.9% mildly.
Krug's team found that patients with a severe deficiency had average A1c's of 8.1%, while those with normal vitamin D levels averaged 7.1% -very close to the "ideal" 7% level advocated by the American Diabetes Association. Ethnic differences also emerged: In nonwhites, vitamin D levels generally were lower than in whites. Only eight of the 124 patients tracked took vitamin D supplements.
Previous research has established a link between vitamin D and the regulation of pancreatic beta cells, which produce insulin. However, Krug's research does not establish a direct causal link between vitamin D deficiency and poor glycemic control in type 2. For one thing, a significant percentage of the U.S. population is considered to be vitamin D deficient*, but does not suffer from poor glycemic control. This means that the vitamin D deficiency in type 2 may simply correlate with patients' already poor glycemic control, brought on by lack of exercise and poor dietary choices.
Vitamin D, considered essential to the maintenance of bone strength, may also affect cardiovascular health and immune system functioning, as well as insulin production. Most people derive the vitamin from exposure to sunlight, although fish and dairy products are also good sources. Current medical guidelines call for 200 IU (international units) of vitamin D daily for people up to age 50; 400 IU for people ages 51 to 70; and 600 IU for people 71 and older.
The study does show that type 2 patients and their doctors should be aware of vitamin D deficiency and its possible effect on good glycemic control. Diet, supplements, and exposure to sunlight through outdoor exercises and activities are simple ways for people with type 2 diabetes to obtain adequate amounts of vitamin D.
Krug presented her findings recently at ENDO 2010, the annual meeting of The Endocrine Society, in San Diego, California.
*According to 2005-2006 data from the National Health and Nutrition Examination Survey, 29% of U.S. men and 17% of U.S. women aged 19 and older derive sufficient vitamin D intake from food alone. Overall, only about one-third of the U.S. population derives sufficient vitamin D just from eating. However, 37% of the population takes vitamin supplements, which probably significantly boosts the percentage of people getting adequate vitamin D. Still, even in a best-case scenario, at least 30% of the population can be considered vitamin D deficient.