Annual High-Dose Vitamin D and Fractures in Older Women

Although vitamin D supplementation is widely assumed to lower fracture risk in older women, previous trials have yielded conflicting results. Because adherence to daily supplementation can be problematic, Australian investigators randomized 2317 community-dwelling women (mean age, 76) at high risk for fracture to receive single annual oral doses of vitamin D (500,000 IU) or placebo for 3 to 5 years. Women were excluded if they already took daily vitamin D (≥400 IU) or any antifracture therapy. Most participants took ≥800 mg of calcium daily.

Median baseline 25-hydroxyvitamin D blood levels were about 20 ng/mL. Blood levels at 1 month, 3 months, and 1 year after vitamin D dosing were 2.4-fold, 1.8-fold, and about 50% higher, respectively, in …