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Estimation of the dietary requirement for vitamin D in healthy adults^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, United Kingdom (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: Knowledge gaps have contributed to considerable variation among international dietary recommendations for vitamin D.

Objective: We aimed to establish the distribution of dietary vitamin D required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above several proposed cutoffs (ie, 25, 37.5, 50, and 80 nmol/L) during wintertime after adjustment for the effect of summer sunshine exposure and diet.

Design: A randomized, placebo-controlled, double-blind 22-wk intervention study was conducted in men and women aged 20–40 y (n = 238) by using different supplemental doses (0, 5, 10, and 15 µg/d) of vitamin D₃ throughout the winter. Serum 25(OH)D concentrations were measured by using enzyme-linked immunoassay at baseline (October 2006) and endpoint (March 2007).

Results: There were clear dose-related increments (P < 0.0001) in serum 25(OH)D with increasing supplemental vitamin D₃. The slope of the relation between vitamin D intake and serum 25(OH)D was 1.96 nmol·L^–1·µg^–1 intake. The vitamin D intake that maintained serum 25(OH)D concentrations of >25 nmol/L in 97.5% of the sample was 8.7 µg/d. This intake ranged from 7.2 µg/d in those who enjoyed sunshine exposure, 8.8 µg/d in those who sometimes had sun exposure, and 12.3 µg/d in those who avoided sunshine. Vitamin D intakes required to maintain serum 25(OH)D concentrations of >37.5, >50, and >80 nmol/L in 97.5% of the sample were 19.9, 28.0, and 41.1 µg/d, respectively.

Conclusion: The range of vitamin D intakes required to ensure maintenance of wintertime vitamin D status [as defined by incremental cutoffs of serum 25(OH)D] in the vast majority (>97.5%) of 20–40-y-old adults, considering a variety of sun exposure preferences, is between 7.2 and 41.1 µg/d.

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