Getting enough vitamin D has long been associated with maintaining healthy bones, and now a new international study gives some idea of how much supplementation an older person needs to prevent fractures.

The study, published Wednesday in the New England Journal of Medicine (NEJM), suggests 800 international units (IU) daily of vitamin D may help reduce the risk of hip and other bone fractures.

Researchers from Europe and the United States noted in their study that 75 per cent of fractures occur in people age 65 and older, and that by 2050, the worldwide incidence of hip fractures is expected to increase by 240 per cent among women and 310 per cent among men.

While one highly touted method to prevent fractures is vitamin D supplementation, previous studies — involving meta-analyses and one pooled participant-level analysis — haven't agreed on that strategy.

For the NEJM study, researchers aimed to measure the effects of supplementation according to the actual intake of each study subject, rather than just the dose each was randomly assigned.

The researchers pooled data from 11 double-blind, randomized control trials of vitamin D supplementation daily, weekly or every four months — with or without calcium — as compared with placebo or calcium alone in people 65 or older. They included 31,022 people — their average age was 76 and 91 per cent of the total were women — with 1,111 hip fractures (four per cent of participants) and 3,770 non-vertebral fractures (12 per cent).

High-dose vitamin D supplementation "was somewhat favourable" in preventing fractures, the study concludes, adding that taking that taking less than about 800 IU daily, with or without calcium, had no effect on bone-fracture risk when compared with taking a placebo or a calcium supplement alone. However, taking 800 IU or more daily drove down the risk of hip fracture by 30 per cent and the risk of other bone fractures by 14 per cent.

Dr. Heike Bischoff-Ferrari of the Center on Aging and Mobility at the University of Zurich says the study could have major public health implications.

Studies produce conflicting results

In an editorial accompany the study in the NEJM, Dr. Robert P. Heaney, M.D., an osteoporosis researcher and professor of endocrinology at Creighton University in Omaha, said there is no shortage of studies probing the benefits of vitamin D.

"There has been more ink spilled over the efficacy of vitamin D than over that of most nutrients, with the possible exception of sodium," he writes.

But he adds that the latest findings may help explain why previous studies have produced conflicting results.Studies on how much vitamin D supplementation is needed have produced conflicting results, but new research released Wednesday suggests 800 IU may be best to prevent fractures in older adults. (Andrew Vaughan/Canadian Press)

“All of the problems with previous studies come from a very modest dose of vitamin D,” writes Heaney. “If you don’t give [study subjects] enough of the vitamin D, then you won’t see an effect."

Given the latest findings, "it would appear to be prudent, and probably helpful as well, to ensure an intake at the upper end of the range," he says, warning that the dose needed to promote bone health may vary depending on a person's baseline vitamin D level.

Osteoporosis Canada, which says at least one in three women and one in five men will suffer a fracture as a result of the brittle-bone disease, recommends routine vitamin D supplementation year round.