A meta-analysis was performed of 5 randomized double-blind trials (n = 9,292) of vitamin D3 supplementation for hip fracture prevention and 7 randomized double-blind trials (n = 9,820) of vitamin D3 supplementation for prevention of non-vertebral fractures. All participants were at least 60 years of age. A dose of 700 to 800 IU/day reduced the relative risk (RR) of hip fracture by 26% (3 trials with 5,572 persons; pooled RR = 0.74; 95% confidence interval [CI], 0.61-0.88) and any non-vertebral fracture by 23% (5 trials with 6,098 persons; pooled RR = 0.77; 95% CI, 0.68-0.87) vs. calcium or placebo. No significant benefit was observed with 400 IU/day of vitamin D (2 trials with 3,722 persons; pooled RR for hip fracture = 1.15; 95% CI, 0.88-1.50; and pooled RR for any non-vertebral fracture = 1.03; 95% CI, 0.86-1.24).

Comment: Vitamin D plays a role in calcium absorption, and vitamin D deficiency causes bone abnormalities including osteoporosis or osteomalacia. In addition, vitamin D deficiency can result in poor balance and proximal muscle weakness, both of which increase the risk of falling. Several clinical trials have shown that supplementation of elderly people with 800 IU/day of vitamin D reduced the number of falls by nearly 50%. The reduction in fracture risk associated with vitamin D supplementation is probably due to a combination of stronger bones and less falling.

The Adequate Intake for vitamin D, as established by the Institute of Medicine of the National Academy of Sciences, is 400 IU/day for adults aged 51-70, and 600 IU/day for people aged 71 and older. Vitamin D requirements tend to increase with advancing age, because the capacity of the skin to synthesize vitamin D decreases as people get older. In addition, many elderly people are housebound, and fail to obtain adequate amounts of sunlight to protect against vitamin D deficiency. The results of the present study suggest that 400 IU/day of vitamin D is insufficient for elderly people, and that a dose of 800 IU/day is more effective for fracture prevention. The Institute of Medicine has set the "safe upper limit" for vitamin D at 2,000 IU/day, but some research suggests that as much as 4,000 IU/day is safe for the average person.

Bischoff-Ferrari HA, et al. Fracture prevention with vitamin D supplementation: a meta-analysis of randomized controlled trials. JAMA 2005;293:2257-2264.