Heike A. Bischoff-Ferrari, PhD, University of Zurich, University Hospital, Zurich, Switzerland, and colleagues performed a meta-analysis on 12 previously published clinical trials of oral vitamin D supplements among adults aged 65 years or older.

The double-blind randomised trials involved 42,279 participants (mean age, 78 years) and looked at non-vertebral fractures, including 8 trials of 40,886 participants specifically studying hip fractures.

When the results of the trials were pooled, vitamin D supplements decreased the risk of non-vertebral fractures by 14% and of hip fractures by 9%.

The authors then pooled the results of only the 9 trials in which participants received doses of more than 400 international units per day. At this dosage, vitamin D supplements reduced non-vertebral fractures by 20% and hip fractures by 18%.

Doses of 400 international units per day or lower did not reduce the risk of either fracture type.

A greater reduction in risk was also seen among trial participants whose blood levels of 25-hydroxyvitamin D achieved a greater increase.

Among individuals taking high doses of vitamin D, additional calcium did not appear to have any further protective effect against fractures. "Physiologically, the calcium-sparing effect of vitamin D may explain why we did not see an additional benefit of calcium supplementation at a higher dose of vitamin D," the authors wrote.

"The greater fracture reduction with a higher received dose or higher achieved 25-hydroxyvitamin D levels for both any non-vertebral fractures and hip fractures suggests that higher doses of vitamin D should be explored in future research to optimise anti-fracture efficacy," they concluded.

"Also, it is possible that greater benefits may be achieved with earlier initiation of vitamin D supplementation and longer duration of use. Our results do not support use of low-dose vitamin D with or without calcium in the prevention of fractures among older individuals."

SOURCE: Archives of Internal Medicine

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