Estimation of the dietary requirement for vitamin D in healthy adults

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.