The Recommended Dietary Allowance (RDA) of vitamin D for older adults is between 400 and 600 International Units (IU) per day. In their review of the existing literature, a team of scientists including senior author Bess Dawson-Hughes, MD, director of the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition and Research Center on Aging at Tufts University, found that this dose was not effective in reducing nonvertebral fracture rates among study participants. The researchers concluded, though, that higher daily doses, in the range of 700 to 800 IU, may reduce the risk of fracture by approximately 25 percent.
Dawson-Hughes and her colleagues analyzed the results of seven experimental trials that all compared fracture rates among subjects 60 years of age and older given vitamin D supplements (with or without calcium supplements) to those among similar subjects given only calcium or placebo. Each study lasted between one and five years, and looked specifically at hip fractures or other fractures that did not involve the spine. The researchers found that only subjects receiving higher doses of vitamin D supplementation had significantly fewer fractures than did subjects in the comparison groups.
"In the future, we may need to reconsider the current recommended daily values of vitamin D for older adults," says Dawson-Hughes. She adds, "We also need to look more closely at the possible role that calcium supplementation may have in mediating the effects of vitamin D. Fractures in the elderly can lead to severe health consequences, including death. One promising prevention strategy may be dietary supplementation with both calcium and vitamin D."
Another meta-analysis on vitamin D published in JAMA last year found that older adults can reduce their risk related to falls by more than 20 percent by ensuring they get enough vitamin D. Dawson-Hughes, an author on that paper, noted that "vitamin D may also improve muscle strength, thereby reducing fracture risk through fall prevention."
Bischoff-Ferrari HA, Willett WC, Wong JB, Giovannucci E, Dietrich T, Dawson-Hughes B. Fracture prevention with vitamin D supplementation: A meta-analysis of randomized controlled trials. JAMA. 2005;293(18): 2257-2264.