Increased intakes of calcium and vitamin D may improve the regulation of insulin levels, and offer protection against diabetes, independent of dairy intake, suggests a new Harvard study. The new study specifically looked at a protein in the blood called C-Peptide because C-peptide is found in the blood in amounts equal to the level of insulin in the blood. Insulin is released from your pancreas and is used by the body to control blood sugar levels. Before it becomes active, insulin and C-peptide are linked together when first made by the pancreas (C-peptide stands for connecting peptide). Therefore the level of C-peptide in the blood can show how much insulin is being made by the pancreas. C-peptide is often used as a measure of insulin levels - insulin is produced in the body by splitting so-called pro-insulin, forming one insulin molecule and one C-peptide.
Dr. Edward Giovannucci and his team 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 (Vol. 92), 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.
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. The Boston-based researchers report that C-peptide levels were 20 % lower in men with the highest blood levels of 25(OH)D.
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 Dr. Giovannucci et al combined calcium intake and blood levels of 25(OH)D, they found that the highest levels were associated with 35 and 12 per cent lower levels of C-peptide. However, no benefits were observed when the researchers considered dairy intake, a result that is at odds with the earlier meta-analysis and review. The study is published in the January 13th, 2009 issue of the Journal of Nutrition.
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