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Maintaining adequate levels of vitamin D during winter months requires a daily dose of 20 micrograms, four times the current recommended dose, according to a new study.

U.S. researchers recruited 112 women with an average age of 22.2 who were assigned to receive a placebo from March 2005 until September 2005, and then randomly assigned to receive either placebo or a daily vitamin D3 supplement (20 micrograms) until February 2006 (1). The researchers found that, among the 86 women who completed the study, those receiving the daily vitamin D supplements experienced increases of 25-hydroxyvitamin D (25(OH)D) blood serum levels of 35.3 nanomoles per liter, compared to only 10.9 nanomoles per liter in the placebo group.

The scientists concluded that daily supplementation with 20 micrograms of vitamin D3 during winter achieved optimal 25(OH)D concentrations (at least 75 nmol/L) in 80 percent of participants, indicating that this dose is adequate to optimize vitamin D status in most young women in the northeastern United States.

The study has important implications for ongoing consultations on vitamin D recommendations, with the current level of five micrograms (200 International Units) seen by many as insufficient. Current recommended daily intakes (RDIs) of vitamin D are 200 IU for people up to 50 years of age, 400 IU for people between 51 and 70, and 600 IU for over the 70s years.

There have been repeated calls in scientific and public circles for an increase in recommended consumption levels of the vitamin in light of research indicating the protective effects that vitamin D may have against conditions such as diabetes, heart disease and cancer.

1. Nelson M. L. et al. Supplements of 20 micrograms/day Cholecalciferol Optimized Serum 25-Hydroxyvitamin D Concentrations in 80% of Premenopausal Women in Winter. Journal of Nutrition, 2009; 139:540–546.