Long-term vitamin D3 supplementation is more effective than vitamin D2 in maintaining serum 25-hydroxyvitamin D status over the winter months

Abstract

Public health recommendations do not distinguish between vitamin D 2 and vitamin D 3, yet disagreement exists on whether these two forms should be considered equivalent. The objective of the present study was to evaluate the effect of a daily physiological dose of vitamin D 2 or vitamin D 3 on 25-hydroxyvitamin D (25(OH)D) status over the winter months in healthy adults living in Dunedin, New Zealand (latitude 46°S). Participants aged 18–50 years were randomly assigned to 25 μg (1000 IU) vitamin D 3 (n 32), 25 μg (1000 IU) vitamin D 2 (n 31) or placebo (n 32) daily for 25 weeks beginning at the end of summer. A per-protocol approach, which included ≥ 90 % supplement compliance, was used for all analyses. Serum 25-hydroxyvitamin D 3 (25(OH)D 3), 25-hydroxyvitamin D 2 (25(OH)D 2) and parathyroid hormone (PTH) were measured at baseline and at 4, 8, 13 and 25 weeks. Geometric mean total serum 25(OH)D concentrations (sum of 25(OH)D 2 and 25(OH)D 3) at baseline was 80 nmol/l. After 25 weeks, participants randomised to D 2 and placebo had a significant reduction in serum 25(OH)D 3 concentrations over the winter months compared with vitamin D 3-supplemented participants (both P< 0·001). Supplementation with vitamin D 2 increased serum 25(OH)D 2 but produced a 9 (95 % CI 1, 17) nmol/l greater decline in the 25(OH)D 3 metabolite compared with placebo (P< 0·036). Overall, total serum 25(OH)D concentrations were 21 (95 % CI 14, 30) nmol/l lower in participants receiving vitamin D 2 compared with those receiving D 3 (P< 0·001), among whom total serum 25(OH)D concentrations remained unchanged. No intervention-related changes in PTH were observed. Daily supplementation of vitamin D 3 was more effective than D 2; however, the functional consequence of the differing metabolic response warrants further investigation.