Study: Megadoses of Vitamin D Offer No Benefit
Sometimes too much of a good thing can be … not such a good thing. That’s the conclusion of the largest study to date of the effects of giving superdoses of vitamin D. The supplement helps bodies build bone and muscle, but the new study, published this week in the Journal of the American Medical Association (JAMA), finds that megaquantities of the vitamin – a year’s supply given in an single dose, for instance – do not appear to reduce the risk of falling or suffering fractures in elderly women.
Most adults in developed nations, including the U.S., are vitamin D deficient, in large part because of lack of sun exposure. While the body naturally produces vitamin D when the skin is exposed to ultraviolet rays, concerns about skin cancer and the heavy use of sunscreens have contributed to a worrying deficiency in large populations. That’s why researchers continue to study the most effective dosing regimen for vitamin D supplementation, particularly in the elderly who are at increased risk for falls and fractures, which are a major cause of death. (See the top 10 medical breakthroughs of 2009.)
Encouraged by previous studies showing that 500,000 IU of vitamin D, given over multiple doses over a short period of time, and a single injection of 300,000 IU improved balance and strength and reduced fractures, Australian scientists at the University of Melbourne expected that a walloping single oral dose of 500,000 IU would also be effective. The study, led by Geoffrey Nicholson and Kerrie Sanders, involved 2,256 women, ages 70 years or older, who were considered to be at high risk of fracture. They were randomly assigned to receive 500,000 IU of cholecalciferol (a form of vitamin D) or placebo once a year for up to 5 years.
To the researchers’ surprise, women who received vitamin D actually suffered more falls and fractures than women who got the placebo pill. The trial participants experienced a total of 5,404 falls over the course of the study; compared with the placebo group, women taking the vitamin D megadose experienced 15% more falls and 26% more fractures.
Although women in the treatment group did have higher blood levels of vitamin D throughout the year than their placebo-taking counterparts, the added vitamin offered no protection again broken bones. “People have been exploring what is the upper limit of dosing that can be given,” says Nicholson, head of the department of clinical and biomedical sciences at the University of Melbourne. “And I think we inadvertently exceeded it. I think the take home message is that megadoses are not safe; that’s certainly going to be our approach until we have evidence to the contrary.”