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Lack of vitamin D tied to insulin resistance
  By David Douglas
NEW YORK (Reuters Health) - Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction, even in glucose-tolerant subjects, according to California-based researchers.
"Low vitamin D is extremely common," lead investigator Dr. Ken C. Chiu told Reuters Health. Moreover, "our observations indicate that low vitamin D has a small but significant impact" on blood glucose metabolism and diabetes, he said.
In the May issue of the American Journal of Clinical Nutrition, Dr. Chiu and colleagues at the University of California, Los Angeles note that they came to this conclusion after a study involving 126 healthy, glucose-tolerant subjects.
Analysis showed that 25-hydroxyvitamin D concentration was positively correlated with insulin sensitivity index and first- and second-phase insulin responses assessed using a hyperglycemic clamp. However, only the correlation with insulin sensitivity index was confirmed with further analysis.
Nevertheless, there was an independent negative correlation of vitamin D concentration and plasma glucose concentration at fasting and at 60, 90 and 120 minutes during oral glucose tolerance tests.
Overall, subjects with concentrations of vitamin D below 20 ng per mL had a greater prevalence of components of metabolic syndrome than did those with higher concentrations. In particular, 14 of 49 subjects with hypovitaminosis D (30%) were deemed at risk of the syndrome versus 9 of 79 without such deficiency (11%).
Thus the researchers conclude that low vitamin D leads to insulin resistance and beta cell dysfunction.
"Now, we have one more reason to keep up vitamin D," Dr. Chiu added. However, he also emphasized that "correction of low vitamin D itself is not sufficient in the treatment of these conditions and too much vitamin D could also be harmful."
Am J Clin Nutr 2004;79:820-825.


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