NEW YORK (Reuters Health) -- The risk of hip fracture appears to be reduced by oral vitamin D supplements only if they are accompanied by additional calcium, according to a report in The Journal of Clinical Endocrinology & Metabolism.

"Supplementation should be targeted to individuals with insufficiencies," Dr. Steven Boonen from Katholieke Universiteit Leuven, Belgium told Reuters Health. This includes individuals older than 75 years; those who are home bound or institutionalized; patients with a diagnosis of osteoporosis; and individuals on steroids or other drugs that decrease bone mineral density.

Boonen and his associates compared the risk of hip fracture using data from vitamin D trials and from vitamin D plus calcium trials. Both compared the supplements with placebo or no treatment.

The risk of hip fracture in the vitamin D-only trials was not statistically significant, the authors report. In contrast, the hip fracture risk in the vitamin D plus calcium trials was reduced by 18 percent, the report indicates.

Combining the data yielded a statistically significant 25-percent lower risk of hip fracture, in favor of vitamin D with additional calcium.

With aging comes a negative calcium balance and for most people this is "due to the combination of inadequate calcium intake and suboptimal vitamin D status," Boonen said. "That is why, in most individuals, a combination of calcium and vitamin D is required to restore calcium balance and reduce fracture risk." "Current evidence indicates that you need at least 800 IU of vitamin D to reduce fracture risk (and that you need additional calcium supplements), but what we don't know is whether 800 IU of vitamin D is the optimal dose for musculoskeletal health," Boonen added. "Future research should focus on this question."