Lee Swanson Research Update

Calcium, Vitamin D Appear to Improve Insulin Levels

April 2009

Increased intakes of calcium and vitamin D may improve insulin levels and offer protection against diabetes, independent of dairy intake.

Writing in the Journal of Nutrition, Tianying Wu, Walter C. Willett and Edward Giovannucci from Harvard School of Public Health report that women with high intakes of calcium had 20% lower levels of C-peptide, a marker of insulin levels, while men with high vitamin D levels had similarly lower levels of the marker.

"The results suggest that calcium intake or systemic vitamin D status, after adjustment for intake of dairy products, is associated with decreased insulin secretion," they wrote.

The study is in-line with previous reports, including a meta-analysis and review published in 2007 in the Journal of Clinical Endocrinology & Metabolism, which found that the data from observational studies showed a "relatively consistent association" between low intakes of calcium, vitamin D, or dairy intake and type 2 diabetes, with highest levels associated with a 64% lower prevalence of the disease, and a 29% lower prevalence of metabolic syndrome among non-blacks.

When intake of calcium and vitamin D was combined, the inverse associations were still observed, with the highest versus lowest combined intake being associated with an 18% lower incidence of diabetes.

The new study used data from healthy men participating in the Health Professionals Follow-Up Study, and healthy women participating in the Nurses’ Health Study I. Intakes of total calcium and vitamin D and blood levels of 25 hydroxyvitamin D (25(OH)D), the storage form of vitamin D in the body, and fasting levels of C-peptide were measured.

C-peptide is often used as a measure of insulin levels—insulin is produced by splitting so-called pro-insulin, which forms one insulin molecule and one C-peptide.

The Boston-based researchers report that C-peptide levels were 20% lower in men with the highest blood levels of 25(OH)D, but no such association was observed in women.

On the other hand, the highest levels of calcium were associated with a 20% reduction in C-peptide levels in women, and a 17% reduction in men, compared to those with the lowest levels.

When Wu, Willett and Giovannucci combined calcium intake and blood levels of 25(OH)D, they found that the highest levels were associated with 35% and 12% lower levels of C-peptide.

Journal of Nutrition 139(3):547-554, 2009

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