Estimation of the dietary requirement for vitamin D in free-living adults >=64 y of age.
What this study found
Daily vitamin D3 increased late-winter serum 25(OH)D in a dose-related manner, and the findings support modest supplementation for many healthy older adults at these latitudes. End-of-study median 25(OH)D was 41.6 nmol/L with placebo, 53.2 with 5 µg/day, 69.5 with 10 µg/day, and 73.8 with 15 µg/day. The treatment-by-time interaction was significant (P = 0.004), and the postintervention comparison across groups was highly significant (P < 0.0001). The estimated slope relating total vitamin D intake to serum 25(OH)D was 1.97 nmol/L per µg/day, with no adverse events reported.
- Study & population
- Dose-ranging interventional study in apparently healthy, free-living white men and women aged 64 years or older recruited from Cork and Coleraine.
- Intervention
- Daily oral vitamin D3 capsules were given for 22 weeks at 5, 10, or 15 µg/day, with a placebo comparator arm.
- Key limitation
- The study was short, winter-only, and limited to healthy white adults aged 64 years or older living at 51-55°N, which narrows generalizability.
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Open PDFOriginal abstract
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 microg vitamin D(3)/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 D(3) intakes. The slope of the relation between total vitamin D intake and serum 25(OH)D was 1.97 nmol . L(-1) . microg 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 microg/d. Intakes were 7.9 and 11.4 microg/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 microg/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 microg 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.