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The Role of Skeletal Muscle in Maintaining Vitamin D Status in Winter

Rebecca S Mason, Mark S Rybchyn, Myriam Abboud, Tara C Brennan-Speranza, David R Fraser
Current Developments in Nutrition ; doi:10.1093/cdn/nzz087

Abstract: Vitamin D status is determined mainly by its formation in skin by the photochemical action of solar UVB light on precursor, 7-dehydrocholesterol. Because of seasonal variation in intensity of solar ultraviolet light, vitamin D status falls in winter and rises in summer. It has been presumed that there is no functional store of vitamin D. Thus, to avoid deficiency, a nutritional supply would be required in winter. However, there is now evidence that the main circulating metabolite of vitamin D, 25-hydroxyvitamin D, accumulates in skeletal muscle cells which provide a functional store during the months of winter. The mechanism is mediated by muscle cell uptake of circulating vitamin D-binding protein (DBP) through a megalin-cubilin membrane transport process. DBP then binds to cytoplasmic actin to provide an array of high affinity binding sites for 25-hydroxyvitamin D. The repeated passage of 25-hydroxyvitamin D into and out of muscle cells would account for its long residence time in blood.
Keywords: Protein / functional / solar / winter / Skeletal / vitamin D status / DBP / Store / hydroxyvitamin

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