No hip fracture reduction with vitamin D supplementation
MedWire News: Hip fractures are not prevented by high or low dose vitamin D supplementation, say UK and Australian scientists who ascribe the observed low level of serum vitamin D in fracture cases in their meta-analysis to confounding factors.
Despite conflicting evidence from randomized controlled trials (RCTs), vitamin D supplementation for the prevention of fractures is widespread, note Jeffrey Lai, from the Australian National University in Canberra, and colleagues.
To examine the current evidence regarding associations between vitamin D, parathyroid hormone (PTH), and hip fracture risk, the team conducted a meta-analysis of existing data. They also undertook separate meta-analyses of RCTs examining vitamin D supplementation and hip fracture, and observational studies of serum vitamin D status via 25-hydroxyvitamin D (25[OH]D) levels, PTH, and hip fracture.
Seven RCTs recording hip fractures in 801 patients were identified, alongside 17 case–control (n=1903) and three cohort studies (n=51,414) of hip fracture and serum 25(OH)D levels, and 10 case–control studies of PTH and hip fracture (n=905).
Overall, there was no significant difference in hip fracture risk in RCTs between patients randomly assigned to receive cholcalciferol or ergocalciferol supplementation versus placebo/control, at a relative risk of 1.13. There were also no significant differences between trials in which doses of less than800 IU/day and 800 IU/day or more were administered, at relative risks of 1.14 and 1.12, respectively.
Serum 25(OH)D levels were 33% lower in hip fracture cases than in controls in case–control studies. There were significant differences in the summary results between population-based and hospital-based studies, with reductions in serum 25(OH)D levels between cases and controls of 40% and 24%, respectively, despite there being significant heterogeneity between the studies.
The team reports in the journal BMC Public Health that the results from the cohort studies concerning the association between serum 25(OH)D and hip fracture showed essentially similar findings, with an apparent dose-related increase in hip fracture for lower serum 25(OH)D levels. There were no significant differences in serum PTH levels between hip fracture cases and controls.
They conclude: “A summary of the best available evidence shows that neither higher nor lower dose vitamin D supplementation prevents hip fracture.
“Randomized and observational findings on vitamin D and hip fracture appear to differ. The reason for this is unclear; one possible explanation is uncontrolled confounding in observational studies.”
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By Liam Davenport