In the first study, published inOsteoporosis International, 160 healthy postmenopausal Brazilian women, ages 50 to 65, took vitamin D capsules (1,000 IU a day) or a placebo. After nine months those taking the vitamin experienced a significant increase in leg muscle strength compared to the placebo group and lost less lean body mass (muscle and bone). The women had relatively low initial blood levels of vitamin D. Most people lose muscle after age 50, typically 1 to 2 percent a year.
In the second study, published in JAMA Internal Medicine, postmenopausal women who took high doses of vitamin D for a year did not have better bone mineral density or muscle strength than women taking lower doses or a placebo, nor did they have a reduced risk of fractures or falls. The women initially had blood levels of vitamin D considered insufficient by many experts (below 30 ng/mL). The high dose (50,000 IU twice a month) raised the average blood level from of 21 to 56 ng/mL; the lower dose, 800 IU a day, raised it to 28 ng/mL.
Research on vitamin D—for muscle health and other proposed benefits—has been inconsistent, and the final verdict will have to wait until four much larger, longer clinical trials report their results in a few years.
See also: Vitamin D: What's the Latest?