The effect of a single, large bolus of vitamin D in healthy adults over the winter and following year: a randomized, double-blind, placebo-controlled trial

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 D-3 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 D-3 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 D-3 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 D-3 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.