Supplementation with high doses of vitamin D in postmenopausal women was not associated with improvements in bone mineral density, muscle function, muscle mass, or falls, according to the results of a trial published online August 3 in JAMA Internal Medicine.

Karen E. Hansen, MD, MS, and colleagues compared the effects of placebo, low-dose cholecalciferol (800 IU of vitamin D3 daily), and high-dose cholecalciferol (50,000 IU of vitamin D3 twice monthly) on changes in bone and muscle outcomes after one year in 230 postmenopausal women aged 75 years or younger with vitamin D insufficiency (baseline levels of 25-hydroxyvitamin D at 14 ng/mL to 27 ng/mL) and no osteoporosis. 

The researchers found that calcium absorption increased by 1% in those taking a high dose of vitamin D, whereas it decreased by 2% in those taking a low dose and by 1.3% in those on placebo. They found no difference among the three groups for changes in bone mineral density (spine, average total-hip, average femoral neck, or total-body), trabecular bone score, muscle mass, sit-to-stand tests, numbers of falls, number of fallers, physical activity, or functional status. 

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The authors noted that their study was limited to one year, and longer exposure to high doses of vitamin D may have a greater effect on bone mineral density.