Journal
CURRENT DEVELOPMENTS IN NUTRITION
Volume 3, Issue 10, Pages -Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/cdn/nzz087
Keywords
vitamin D status; 25-hydroxyvitamin D; seasonal variation; ultraviolet light; vitamin D-binding protein; muscle
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Funding
- Australian Research Council [DP170104408]
- Zayed University
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The status of vitamin D is determined mainly by its formation in skin by the photochemical action of solar UVB light (wavelength 290-320 nm) on the precursor 7-dehydrocholesterol. Because of seasonal variation in intensity of solar UV 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 winter months. 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 [25(OH)D]. The repeated passage of 25(OH)D into and out of muscle cells would account for its long residence time in blood.
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