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nightsurfer on 2009-09-0225-Hydroxylation of vitamin D3: relation to circulating vitamin D3 under various input conditions.
Heaney RP, Armas LA, Shary JR, Bell NH, Binkley N, Hollis BW.
Am J Clin Nutr. 2008 Jun;87(6):1738-42.
Conclusions: At physiologic inputs, there is rapid conversion of precursor to product at low vitamin D3 concentrations and a much slower rate of conversion at higher concentrations. These data suggest that, at typical vitamin D3 inputs and serum concentrations, there is very little native cholecalciferol in the body, and 25(OH)D constitutes the bulk of vitamin D reserves. However, at supraphysiologic inputs, large quantities of vitamin D3 are stored as the native compound, presumably in body fat, and are slowly released to be converted to 25(OH)D.