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Objective. To determine the associations between body adiposity and change in serum 25-(OH)D levels over 2.6 years, and if these associations are mediated by metabolic andinflammatory factors in older adults. Methods. This is a longitudinal study of 859 randomly selected subjects (mean 62 years, range 51–80, 49% women). Serum 25-hydroxyvitamin D [25-(OH)D] was assessed by radioimmunoassay at baseline and 2.6 years later. Baseline serumlevel of leptinwas assessed by radioimmunoassay and interleukin (IL)-6 by a chemiluminescent immunoassay in the first 183 subjects. Results. In multivariable analyses, body mass index, trunk fat percentage and waist-to-hip ratio were significant predictors of increased incident vitamin D deficiency [a 25-(OH)D < 50 nmol L)1 at follow-up when ‡50 nmol L)1 at baseline] and decreased recovery of vitamin D deficiency [a 25-(OH)D ‡ 50 nmol L)1 at follow-up when < 50 nmol L)1 at baseline]. Change in 25-(OH)D levels per annum was also independently predicted by baseline leptin (b: )0.09⁄unit, 95% CI: )0.17, )0.03), IL-6 (b: )0.68⁄ quartile, 95% CI: )1.35, )0.02) and total cholesterol ⁄ high-density lipoprotein (HDL) ratio (b: )0.51, 95% CI: )0.88, )0.14). The associations between body adiposity measures and change in 25- (OH)D completely disappeared after adjustment for leptin, diminished after adjustment for IL-6, but remained unchanged after adjustment for total cholesterol ⁄HDL ratio. All associations were independent of season and sun exposure. Conclusions.Bodyfat isnot simplyapassive reservoir for 25-(OH)D. In addition to season and sun exposure, 25-(OH)D levels appear to be determined by metabolic and, to a lesser extent, inflammatory factors, and these appear to mediate the effects of adiposity onchange in25-(OH)D.

Item Type:	Refereed Article
Keywords:	adiposity, interleukin-6, leptin, lipids, vitamin D deficiency
Research Division:	Biomedical and Clinical Sciences
Research Group:	Clinical sciences
Research Field:	Endocrinology
Objective Division:	Health
Objective Group:	Clinical health
Objective Field:	Clinical health not elsewhere classified
UTAS Author:	Ding, C (Professor Chang-Hai Ding)
UTAS Author:	Blizzard, L (Professor Leigh Blizzard)
UTAS Author:	Burgess, J (Professor John Burgess)
UTAS Author:	Jones, G (Professor Graeme Jones)
ID Code:	65402
Year Published:	2010
Web of Science® Times Cited:	40
Deposited By:	Menzies Institute for Medical Research
Deposited On:	2010-11-11
Last Modified:	2011-05-02
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