RESUMO
BACKGROUND/OBJECTIVES: Although single, high doses of vitamin D effectively maintain vitamin D sufficiency in several populations, no studies have evaluated healthy adults over winter, during which vitamin D status declines. This study investigated whether high-dose vitamin D3 given once to healthy adults before winter will (1) prevent the wintertime decline in vitamin D status, (2) promote vitamin D sufficiency 1 year following the dose and (3) prevent the rise of parathyroid hormone (PTH) concentrations. SUBJECTS/METHODS: In this double-blind, placebo-controlled trial, we assessed plasma 25(OH)D and PTH concentrations at baseline, 5, 90 and 365 days after drug administration in 28 healthy adults. In all, >80% of subjects returned at each time point. RESULTS: At baseline, the young, healthy participants had a mean plasma 25(OH)D concentration of 17.5±6.1 ng/ml. Only two subjects exhibited plasma 25(OH)D concentrations >30 ng/ml. At 5 days, subjects randomized to vitamin D3 had a higher mean plasma 25(OH)D concentration compared with the placebo group (39.1 vs 19.1 ng/ml, P<0.001). Plasma 25(OH)D concentrations returned to baseline at 90 and 365 days in the vitamin D3 group and remained unchanged in the placebo group. PTH and calcium concentrations were unrelated to changes in 25(OH)D levels and similar between groups over time. CONCLUSIONS: A dose of 250,000 IU of vitamin D3 given once in November resulted in a robust increase in plasma 25(OH)D after 5 days, but it was unable to sustain this increase after 90 days. A larger or more frequent dosing regimen may be needed for long-term vitamin D sufficiency.