Older people can prevent fractures by taking vitamin D supplements, a new study confirms, as long as they use a high enough dose-and keep taking it.

"Everyone age 65 and older should take vitamin D in a dose close to 800 IU per day, best as vitamin D3, and with good adherence," Dr. Heike A. Bischoff-Ferrari of the University of Zurich, one of the researchers on the study, told Reuters Health. And it wouldn't be a bad idea for younger adults to follow this recommendation too, she added. "I think if you are young and want to do something early for your bone health that's something to think about."

Recent studies had called into question the benefit of vitamin D for bone health, Bischoff-Ferrari and her team note in the Archives of Internal Medicine, but some of these investigations had not accounted for adherence to supplement use. In one of the studies, the researcher pointed out in an interview, less than half of the people randomized to take vitamin D were actually doing so 2 years later.

To get a better sense of the association between fracture risk and actual vitamin D intake, the researchers pooled the results of 12 randomized controlled trials of oral vitamin D supplementation, taking into account adherence and dose. The studies included a total of 42,279 people and looked at non-vertebral fractures; eight of the studies specifically addressed hip fractures.

Overall, the researchers found, the supplements cut the risk of any non-vertebral fracture by 14 percent, and of hip fractures by 9 percent. While quantities below 400 IU a day had no effect on fracture risk, people who consumed more than 400 IU daily had a 20 percent lower risk of any type of fracture and an 18 percent lower risk of hip fracture.

Recent studies had suggested that vitamin D might only be helpful for people living in nursing homes, or only when taken with extra calcium, Bischoff-Ferrari noted. But the new analysis showed the vitamin actually cut fracture risk by 29 percent for community-dwelling seniors, compared to 15 percent for people living in institutions. The effect of vitamin D was independent of calcium, she added, probably because adequate vitamin D intake helps the body use calcium more efficiently.

Getting people to follow recommendations for preventive treatment can be difficult, Bischoff-Ferrari said. But researchers are now investigating ways to give people vitamin D in weekly or even monthly doses, she added. "We do need more data with that, but this is clearly the future."

Given growing evidence that vitamin D may also lower cancer risk, and the fact that the nutrient is safe at fairly high doses, younger people may want to consider vitamin D supplements too, the researcher said.

"A lot of people think a healthy nutrition is good enough, but unfortunately vitamin D is very hard to cover by food sources," Bischoff-Ferrari added. To get adequate vitamin D through food alone, she explained, a person would need to eat two servings of fatty fish like salmon or mackerel every day.