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Study finds no bone health benefits from high-dose vitamin D in postmenopausal women

High doses of vitamin D may not provide any bone health benefits for postmenopausal women. A new study found that high doses of vitamin D provided only a small increase in calcium absorption after one year, and did not improve bone mineral density, muscle mass or muscle function, and had no effect on incidence of falls.

Low vitamin D levels in postmenopausal women can be a factor in osteoporosis, because vitamin D helps bones absorb calcium. According to background information in the study, almost half of postmenopausal women will have an osteoporotic fracture, but experts disagree on the vitamin D level needed for bone health. For the study, the researchers used 30 ng/ml in blood serum as the optimal level of vitamin D, which is often recommended for postmenopausal women.

Researchers at the University of Wisconsin School of Medicine and Public Health conducted a randomized, double-blind, placebo controlled study of women with low vitamin D levels.

The study involved 230 postmenopausal women under age 75, who had blood serum levels of vitamin D between 14 and 27 ng/ml. None of the women had osteoporosis. The researchers measured all the participants’ total fractional calcium absorption, bone mineral density and muscle fitness at the start of the study.

The women were divided into three groups, and all of them were given pills to take daily, and pills to take twice a month. In the high-dose group, the daily pill was a placebo and the twice-monthly pill was 50,000 IU of a form of vitamin D called cholecalciferol. In the low-dose group, the daily pill was 800 IU vitamin D, and the twice-monthly pill was a placebo. The third group took placebos for all doses, daily and twice-monthly. None of the women or the researchers knew which group any participant was in.

In the high-dose group, the participants’ vitamin D levels rose above the target 30 ng/ml and stayed at that level over the course of the year-long study.

After one year, the researchers compared calcium absorption, bone mineral density, muscle fitness and fall history among the three groups. They found that the high-dose group had a one per cent increase in calcium absorption, while the low-dose group had a two per cent decrease and the placebo group each had a 1.3 per cent decrease. Despite this small difference, there was no difference between the groups in changes in bone mineral density, muscle function or incidence of falls.

These results suggest that using high-dose supplements to maintain vitamin D levels at 30 ng/ml may not benefit bone health in postmenopausal women. However, the researchers also note taking these supplements for longer than the one-year study period may have different results. The results cannot be applied to men, women over age 75 or young adults. Because so few black women participated in the study, the results also may not be applicable to black women.

The study was published by JAMA Internal Medicine on Aug. 3, 1015.

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  • A publication of:
  • Women's College Hospital