Do Vitamin D Supplements Improve Bone Health?

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For many years, Americans — especially postmenopausal women — have been told to take vitamin D and calcium supplements to protect their bones from thinning (osteopenia and osteoporosis) and to reduce their risk of fractures. More recently, some researchers have suggested that extra vitamin D may also strengthen muscles and reduce the risk of falls that lead to bone fractures. Experts have debated what the optimal level of 25-hydroxyvitamin D (25[OH]D) in the blood is for improving both bone and musculoskeletal health. To help clarify the possible benefits of supplemental vitamin D, Dr. Karen Hansen and colleagues compared the effects of giving three groups of post menopausal women either a (1) placebo, (2) low-dose vitamin D3 (a.k.a. cholecalciferol), or (3) high-dose Vitamin D3 for one year. The subjects were older women who initially had low vitamin D status as determined by a low 25(OH)D blood test. This randomized, double-blind, placebo-controlled clinical trial involved 230 postmenopausal women who were 75 years or younger with baseline 25(OH)D levels of between 14 and 27 ng/mL. The researchers looked for changes in total fractional calcium absorption, bone mineral density (BMD), leg muscle strength, and muscle mass. One group received a daily supplement of 800 IU vitamin D3 and twice monthly yellow placebo (n=75), and daily white placebo and twice monthly 50,000 IU vitamin D3 (n=79). The high-dose vitamin D regimen achieved and maintained 25(OH)D levels >30 ng/mL. After one year, changes in total fractional calcium absorption were measured using 2 stable isotopes, and BMD and muscle mass were measured using dual energy x-ray absorptiometry. They used the “Timed Up and Go” test to measure muscle strength and function, and also used a Health Assessment Questionnaire and physical activity questionnaire.

The results of Dr. Hansen’s study showed that after baseline absorption was controlled for, calcium absorption increased 1% (or 10 mg/d) in the high-dose arm but decreased 2% in the low-dose arm (P=.005 vs high-dose arm) and 1.3% in the placebo arm (P=.03 vs high-dose arm). However, they found no significant changes between the groups in spine, mean total-hip, mean femoral neck, or total-body BMD, trabecular bone score, muscle mass, and Timed Up and Go or five sit-to-stand test scores. They also found nothing between group differences for the numbers of falls, number of fallers, physical activity, or functional status. The researchers concluded that high-dose Vitamin D3 therapy did modestly increase calcium absorption, but the effect was small and it did not translate into measurable beneficial effects on BMD, muscle function, muscle mass, or falls or fractures after one year. This data provides very little support for the views of some experts who recommend maintaining serum 25(OH)D levels of 30 ng/mL or higher in postmenopausal women. Instead, they found that both the low- and high-dose Vitamin D3 supplements failed to provide any measurable health benefit compared to a placebo (such as improved bone health or improved muscle strength or function) in this group of postmenopausal women whose initial 25(OH)D levels were less than 30 ng/mL. This suggests that most older women with 25(OH)D levels in the 20s or higher are unlikely to benefit from taking either an RDA dose or a much higher dose of supplemental vitamin D (1).

Dr. Rita Redberg, a professor of medicine with the University of California, San Francisco’s Philip R. Lee Institute for Health Policy Studies and editor of JAMA Internal Medicine, went a step further. She said “I think this is the final, and negative, word on vitamin D supplementation. There are a lot of women getting vitamin D blood tests and taking vitamin D supplements of various doses. This study suggests that those practices should stop. In other words, if you are going to start vitamin D to improve bone health, and if you are currently taking it for that reason, you can stop. I know of no other benefits for vitamin D supplementation.”

Bottom Line:

While some researchers continue to suggest that many Americans have insufficient vitamin D status and are recommending blood levels of 25(OH)D of 30ng/ml to assure stronger bones and muscles, the data from this recent study suggests that blood levels above 15ng/ml (and certainly above 20ng/ml) indicate vitamin D nutriture is adequate at least for maintaining bone and muscle health in post-menopausal women.

References:

  1. E. Hansen; R. E. Johnson; K. R. Chambers; et.al. Treatment of Vitamin D Insufficiency in Postmenopausal Women: : A Randomized Clinical Trial. Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison Quality and Patient Safety Analysis, Saint Luke’s Health System, Kansas City, Missouri Department of Computing and Biometry, University of Wisconsin College of Agriculture and Life Sciences, MadiJAMA Intern Med. Published online August 03, 2015. doi:10.1001/jamainternmed.2015.3874.

By James J. Kenney, PhD, FACN

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