Although vitamin D is essential to bone health, a controlled clinical trial published online by JAMA Internal Medicine on Aug. 3, 2015, found that vitamin D supplements didn't build bone in postmenopausal women with blood levels of vitamin D below the 30-ng/mL threshold generally considered necessary for good health. Researchers at the University of Wisconsin randomly assigned 230 women to three groups: one got 800 IU of vitamin D daily and a placebo twice a month; one got a placebo daily and 50,000 IU of vitamin D twice a month; the third got placebos both daily and twice a month. The study lasted a year. The researchers found that neither dose of vitamin D had a significant effect on bone mass, falls, or fractures.

The Wisconsin study may not have used the right doses of vitamin D or lasted long enough to show an effect. One ongoing study, The Vitamin D and Omega-3 Trial (VITAL), is large enough to demonstrate even small-to-moderate benefits of vitamin D supplementation. VITAL is evaluating a 2,000-IU daily dose for five years in 26,000 women and men. The results are expected in 2017. Until then, it's still important to get the recommended daily dose of vitamin D: 600 IU for adults through age 70 and 800 IU for people ages 71 or older