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25-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. PMID: 18541563 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.

Relation of body fat indexes to vitamin D status and deficiency among obese adolescents. Lenders CM, Feldman HA, Von Scheven E, Merewood A, Sweeney C, Wilson DM, Lee PD, Abrams SH, Gitelman SE, Wertz MS, Klish WJ, Taylor GA, Chen TC, Holick MF; Elizabeth Glaser Pediatric Research Network Obesity Study Group. Am J Clin Nutr. 2009 Sep;90(3):459-67. Epub 2009 Jul 29. PMID: 19640956 RESULTS: The mean (+/-SD) age of the adolescents was 14.9 +/- 1.4 y; 38 (66%) were female, and 8 (14%) were black. The mean (+/-SD) body mass index (in kg/m(2)) was 36 +/- 5, FM was 40.0 +/- 5.5%, and VAT was 12.4 +/- 4.3%. Seventeen of the adolescents were vitamin D deficient, but none had elevated PTH concentrations. Bone mineral content and bone mineral density were within 2 SDs of national standards. In a multivariate analysis, 25(OH)D decreased by 0.46 +/- 0.22 ng/mL per 1% increment in FM (beta +/- SE, P = 0.05), whereas PTH decreased by 0.78 +/- 0.29 pg/mL per 1% increment in VAT (P = 0.01). CONCLUSIONS: To the best of our knowledge, our results show for the first time that obese adolescents with 25(OH)D deficiency, but without elevated PTH concentrations, have a bone mass within the range of national standards (+/-2 SD). The findings provide initial evidence that the distribution of fat may be associated with vitamin D status, but this relation may be dependent on metabolic factors

AUGUSTA, Ga. - Too little vitamin D could be bad for more than your bones; it may also lead to fatter adolescents, researchers say.\n\nA Medical College of Georgia study of more than 650 teens age 14-19 has found that those who reported higher vitamin D intakes had lower overall body fat and lower amounts of the fat in the abdomen, a type of fat known as visceral fat, which has been associated with health risks such as heart disease, stroke, diabetes and hypertension

Vitamin D status and its relationship to body fat, final height, and peak bone mass in young women.\nKremer R, Campbell PP, Reinhardt T, Gilsanz V.\nJ Clin Endocrinol Metab. 2009 Jan;94(1):67-73. Epub 2008 Nov 4.\nPMID: 18984659

Decreased bioavailability of vitamin D in obesity. Wortsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Am J Clin Nutr. 2000 Sep;72(3):690-3. Erratum in: Am J Clin Nutr. 2003 May;77(5):1342. PMID: 10966885 Conclusions: Obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D3 from cutaneous and dietary sources because of its deposition in body fat compartments.