Vitamin D supplementation alone does not appear to reduce the risk of fracture, but a combination of vitamin D and calcium may, according to a systematic review and meta-analysis published in JAMA Network Open.
Pang Yao, PhD, from the Nuffield Department of Population Health at the University of Oxford (England) and coauthors wrote that, while randomized, controlled trials (RCTs) of vitamin D supplements – either alone or in combination with calcium supplementation – have found conflicting results, most only had limited power to detect differences in the risk of fracture.
Dr. Yao and associates performed a meta-analysis of 11 observational studies with 39,141 participants, 11 RCTs of vitamin D supplementation alone in 34,243 participants, and 6 RCTs of calcium plus vitamin D involving 49,282 participants.
The analysis of the observational studies revealed that each 10.0-ng/mL increase in blood 25-hydroxyvitamin D concentrations was associated with a 7% lower risk of any fracture. However the authors noted significant heterogeneity between individual studies.
The meta-analysis of the 11 trials of vitamin D alone found that supplementation was not associated with significant change in the risk for any fracture or for hip fracture. Even subgroup analyses looking at age, residential status, location, study design, daily supplementation, or duration of supplementation failed to find any effect. However, there was a median difference in blood 25-hydroxyvitamin D concentrations of 8.4 ng/mL with vitamin D supplementation.
In the meta-analysis of the six vitamin D plus calcium trials, there was a significant 6% reduction in the rate of any fracture and a 16% reduction in hip fracture rate with supplementation. Overall, there was a 1% reduction in the risk of any fracture for each 0.4-ng/mL difference in blood 25-hydroxyvitamin D concentration and 2% reduction in the risk of hip fracture.
However, the authors judged five of those six vitamin D plus calcium trials to be at high risk of bias, with two having open-label designs, although there was little heterogeneity among the studies. All the trials used either 800 or 400 IU/day of vitamin D and 1,200 or 800 mg/day of calcium, and the mean duration of treatment was 5.9 years.
Participants aged 80 years or older living in institutions showed greater reductions in the risk of any fracture with calcium plus vitamin D supplementation, compared with those younger than 80 years who were living in the community.
“In this systematic review and meta-analysis, the available evidence from completed RCTs provided no support for the effects of vitamin D alone on prevention of fracture, but most of these RCTs were constrained by methodological problems,” they wrote. “Meta-analyses of ongoing RCTs assessing the effects of higher daily doses of vitamin D on fracture risk are needed before making recommendations on the use of vitamin D for prevention of fracture.”
One author was supported by a Sino-British Fellowship Trust scholarship, and another received grants from the U.K. Medical Research Council. No conflicts of interest were declared.
SOURCE: Yao P et al. JAMA Netw Open. 2019. doi: 10.1001/jamanetworkopen.2019.17789.