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Estimation of the dietary requirement for vitamin D in free-living adults 64 y of age^1,2,3

¹ From the Departments of Food and Nutritional Sciences (TRH, AJL, NT, KS, SM, AF, MK, and KDC), Medicine (KDC), Epidemiology and Public Health (APF), and Statistics (APF), University College, Cork, Ireland, and the Northern Ireland Centre for Food and Health, University of Ulster, Coleraine, Northern Ireland (GH, MSB, MPB, EMD, JMWW, and JJS).

² Supported by the UK Food Standards Agency.

³ Reprints not available. Address correspondence to KD Cashman, Department of Food and Nutritional Sciences and Department of Medicine, University College, Cork, Ireland. E-mail: k.cashman{at}ucc.ie.

Background: Older adults may be more prone to developing vitamin D deficiency than younger adults. Dietary requirements for vitamin D in older adults are based on limited evidence.

Objective: The objective was to establish the dietary intake of vitamin D required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above various cutoffs between 25 and 80 nmol/L during wintertime, which accounted for the effect of summer sunshine exposure and diet.

Design: A randomized, placebo-controlled, double-blind, 22-wk intervention was conducted in men and women aged 64 y (n = 225) at supplemental levels of 0, 5, 10, and 15 µg vitamin D₃/d from October 2007 to March 2008.

Results: Clear dose-related increments (P < 0.0001) in serum 25(OH)D were observed with increasing supplemental vitamin D₃ intakes. The slope of the relation between total vitamin D intake and serum 25(OH)D was 1.97 nmol · L^–1 · µg intake^–1. The vitamin D intake that maintained serum 25(OH)D concentrations >25 nmol/L in 97.5% of the sample was 8.6 µg/d. Intakes were 7.9 and 11.4 µg/d in those who reported a minimum of 15 min daily summer sunshine exposure or less, respectively. The intakes required to maintain serum 25(OH)D concentrations of >37.5, >50, and >80 nmol/L in 97.5% of the sample were 17.2, 24.7, and 38.7 µg/d, respectively.

Conclusion: To ensure that the vitamin D requirement is met by the vast majority (>97.5%) of adults aged 64 y during winter, between 7.9 and 42.8 µg vitamin D/d is required, depending on summer sun exposure and the threshold of adequacy of 25(OH)D. This trial was registered at http://www.controlled-trials.com/ISRCTN20236112 as ISRCTN registration no. ISRCTN20236112.

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				R. Vieth Experimentally observed vitamin D requirements are higher than extrapolated ones Am. J. Clinical Nutrition, October 1, 2009; 90(4): 1114 - 1115. [Full Text] [PDF]

				K. D Cashman and M. Kiely Reply to R Vieth Am. J. Clinical Nutrition, October 1, 2009; 90(4): 1115 - 1116. [Full Text] [PDF]