Vitamin D is a hormone that research has shown to have been underestimated with regard to its importance in human health. The traditional view of vitamin D is that deficiency leads to the bone diseases osteomalacia in adults and rickets in children. However, over the last decade, mounting evidence suggests that vitamin D insufficiency plays an important role in the aetiology of a number of major diseases. In particular, associations between vitamin D and type I and type II diabetes have been established. The reason for this association is not understood, but may relate to the high parathyroid hormone levels associated with low vitamin D levels. Parathyroid hormone may inhibit insulin synthesis and secretion from the pancreas and cause peripheral insulin insensitivity by regulating intracellular calcium levels. The vitamin D metabolite 1,25-dihydroxyvitmanim D may also directly stimulate expression of the insulin receptor.
Researchers are therefore interested in the association between diabetes and vitamin D plasma concentrations, but many studies have taken single measurements that do not account for seasonal variation. Because of this problem, a group of researchers1 used a predicted vitamin D score to assess the vitamin D status of a number of individuals. This method used potential determinants of plasma 25-hydroxyvitamin D [25(OH)D] concentrations, which removed the seasonal effects on vitamin D by holding the season constant. A total of 133 cases of diabetes were identified from the total sample of 3066 over a 7 year period. Those individuals in the highest tertile for 25(OH)D had a 40% lower incidence of type II diabetes compared to those in the lowest tertile for 25(OH)D, after adjustment for possible confounding variables such as age, hypertension, sex, waist circumference and parental history of diabetes.
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