A daily dose of 400 international units may reduce hip fractures by 18 per cent, and non-vertebral fractures by 20 per, according to pooled data from double-blind randomised controlled trials involving 42,279 participants.
Writing in the Archives of Internal Medicine, authors led by Heike Bischoff-Ferrari from the University of Zurich report that several recent trials have cast doubt on the benefits of vitamin D and fracture risk, “leading to uncertainty among patients and physicians”.
“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 optimize anti-fracture efficacy,” wrote Bischoff-Ferrari and her co-workers.
“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,” they added.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
The importance of dose
Dr Bischoff-Ferrari and her co-workers performed a meta-analysis of 12 published clinical trials involving oral vitamin D supplements in 42,279 adults aged 65 or older. Eight trials specifically studied hip fractures.
Pooling of all the data showed that supplements of vitamin D were associated with a 14 per cent decrease in the risk of non-vertebral fractures and a 9 per cent decrease in the risk of hip fractures.
Furthermore, when the researchers considered only data from nine using doses of vitamin D over 400 IU per day, the supplements were associated with a 20 and 18 per cent reduction in non-vertebral and hip fractures, respectively. Lower doses did not reduce the risk of either fracture type, said the researchers.
While vitamin D’s role in bone health is often associated with calcium, the researchers note that the mineral did not have an additional effect in individuals taking high doses of vitamin D. “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 write.
Source: Archives of Internal Medicine Volume 169, Number 6, Pages 551-561“Prevention of Nonvertebral Fractures With Oral Vitamin D and Dose Dependency A Meta-analysis of Randomized Controlled Trials” Authors: H.A. Bischoff-Ferrari, W.C. Willett, J.B. Wong, A.E. Stuck, H.B. Staehelin, E.J. Orav, A. Thoma, D.P. Kiel, J. Henschkowski