Effect of Vitamins D2 and D3 Supplement Use on Serum 25OHD Concentration in Elderly Women in Summer and Winter

Vitamin D₂ and D₃ are generally considered equipotent in humans. A few studies have reported that serum 25OHD levels are higher in vitamin D₃- compared with vitamin D₂-supplemented subjects. As both vitamin D₂ and D₃ supplements are commonly used by elderly in United States, in the present study we determined the effect of self-reported vitamin D₂ and vitamin D₃ supplement use on serum total 25OHD levels according to season in elderly women aged 65–77 years. Serum total 25OHD levels were determined in winter and summer in unsupplemented women (N = 307) and in women who reported taking vitamin D₂ (N = 56) and vitamin D₃ (N = 55) supplements by competitive protein binding assay. In vitamin D₂-supplemented women, the contribution of vitamin D₂ and D₃ to the mean serum total 25OHD level was assessed by HPLC. In summer, there were no significant differences in the mean total serum 25OHD levels (ng/ml) among the vitamin D₂ (32 ± 2.1), vitamin D₃ (36.7 ± 1.95), and unsupplemented (32.2 ± 0.95) groups. In winter, the mean serum total 25OHD levels were higher in women on vitamin D₂ (33.6 ± 2.34, P < 0.05) and vitamin D₃ (29.7 ± 1.76, NS) supplements compared with unsupplemented women (27.3 ± 0.72). In vitamin D₂-supplemented women, about 25% of the mean serum total 25OHD was 25OHD₂, in both summer and winter. Twelve percent of unsupplemented women and 3.6% of vitamin D-supplemented women had a mean serum total 25OHD level below 15 ng/ml in winter. In elderly subjects, both vitamin D₂ and Vitamin D₃ supplements may contribute equally to circulating 25OHD levels, with the role of vitamin D supplement use being more predominant during winter.This work was presented in part as an abstract at Second Joint Meeting of the American Society for Bone and Mineral Research and The International Bone and Mineral Society, San Francisco, CA, 1–6 December 1998.