June 21, 2010 -- Vitamin D deficiency, long suspected to be a risk factor for glucose intolerance, is commonly found in people with poor diabetes control, according to a new study.
''Our study could not show cause and effect," says Esther Krug, MD, an endocrinologist at Sinai Hospital of Baltimore and assistant professor of medicine at Johns Hopkins University School of Medicine, Baltimore, who presented the findings at ENDO 2010, the annual meeting of The Endocrine Society, in San Diego.
But she did find that vitamin D deficiency was common in her study, with more than 91% of participants deficient. As the deficiency worsened, so did diabetes control. Only eight of the 124 participants took vitamin D supplements, she found.
About 18 million people in the U.S. have been diagnosed with diabetes, according to the American Diabetes Association, and about 6 million more are believed to have the condition but are undiagnosed.
Krug and her colleagues decided to look at vitamin D deficiency in the wake of reports suggesting that vitamin D has an active role in regulating pancreatic beta cells, which make insulin.
So they evaluated the medical charts of 124 people with type 2 diabetes (in which the body doesn't make enough insulin or the cells ignore the insulin) seen at an outpatient clinic from 2003 to 2008. The charts contained information on the patients' age, race, vitamin D levels, calcium intake, family history of diabetes, and results of their hemoglobin A1c blood test. The A1c provides an average measurement of blood sugar control over about a 12-week span. (For people with diabetes, the goal is 7%; for people without, the normal range is 4%-6%.)
Krug's team divided the vitamin D levels they found into four groups: normal (defined in the study as above 32 nanograms per deciliter), mild deficiency, moderate deficiency, or severe.
In all, 113 of the 124 patients (91.1%) were vitamin D deficient -- 35.5% severely, 38.7% moderately, and 16.9% mildly.
The average A1c was higher in patients with severe vitamin D deficiency compared to those with normal levels of vitamin D. Those with severe deficiency had an average of 8.1%; those with normal vitamin D levels averaged 7.1%.
Krug found racial differences. ''In people of color, vitamin D levels were even lower than in Caucasians and they were associated with even poorer diabetes control," she tells WebMD.
Only 6.4% were on vitamin D supplementation. This was true, Krug says, even though they had medical coverage and saw their doctors. She suspects a lack of awareness on the part of the physicians partly explains the frequent deficiencies she found.
Aggressive screening of vitamin D levels is crucial for people with diabetes, Krug says. Once a supplement is recommended, she says, the blood levels should be rechecked to see if the supplement sufficiently increases vitamin D levels.
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