Supplements of 20 microg/d cholecalciferol optimized serum 25-hydroxyvitamin D concentrations in 80% of premenopausal women in winter.

The serum 25-hydroxyvitamin D [25(OH)D] response to daily supplementation with 20 microg cholecalciferol (D3) during winter in predominantly white premenopausal women living in Maine was measured and the effects of body composition and hormonal contraceptive use on baseline serum 25(OH)D concentrations and the response to supplementation were examined. A total of 112 women (22.2 +/- 3.7 y old) received placebo from March 2005 until September 2005 when they were randomized to receive either placebo or 20 microg/d D3 through February 2006. Eighty-six women completed the study. Actual mean D3 content of the supplements was 22 microg per capsule. In February 2005 the serum 25(OH)D concentration was 62.0 +/- 23.4 nmol/L (mean +/- SD). Serum 25(OH)D concentrations increased by 35.3 +/- 23.2 nmol/L from February 2005 to February 2006 in the treatment group, significantly more than the 10.9 +/- 16.9 nmol/L increase in the placebo group. Treatment group, magnitude of summer increase in 25(OH)D, estrogen dose, and baseline serum 25(OH)D concentrations, but not body fat, were significant predictors of the 1-y change in 25(OH)D concentrations used to assess the magnitude of the response to supplementation. Daily supplementation with 20 microg D3 during winter achieved optimal 25(OH)D concentrations (> or = 75 nmol/L) in 80% of participants, indicating that this dose is adequate to optimize vitamin D status in most young women in Maine.