OBJECTIVE: To determine whether increasing calcium intake from dietary sources affects bone mineral density (BMD) and, if so, whether the effects are similar to those of calcium supplements.
DESIGN: Random effects meta-analysis of randomised controlled trials.
DATA SOURCES: Ovid Medline, Embase, Pubmed, and references from relevant systematic reviews. Initial searches were undertaken in July 2013 and updated in September 2014.
ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Randomised controlled trials of dietary sources of calcium or calcium supplements (with or without vitamin D) in participants aged over 50 with BMD at the lumbar spine, total hip, femoral neck, total body, or forearm as an outcome.
RESULTS: We identified 59 eligible randomised controlled trials: 15 studied dietary sources of calcium (n=1533) and 51 studied calcium supplements (n=12,257). Increasing calcium intake from dietary sources increased BMD by 0.6-1.0% at the total hip and total body at one year and by 0.7-1.8% at these sites and the lumbar spine and femoral neck at two years. There was no effect on BMD in the forearm. Calcium supplements increased BMD by 0.7-1.8% at all five skeletal sites at one, two, and over two and a half years, but the size of the increase in BMD at later time points was similar to the increase at one year. Increases in BMD were similar in trials of dietary sources of calcium and calcium supplements (except at the forearm), in trials of calcium monotherapy versus co-administered calcium and vitamin D, in trials with calcium doses of = 1000 versus <1000 mg/day and = 500 versus >500 mg/day, and in trials where the baseline dietary calcium intake was <800 versus = 800 mg/day.
CONCLUSIONS: Increasing calcium intake from dietary sources or by taking calcium supplements produces small non-progressive increases in BMD, which are unlikely to lead to a clinically significant reduction in risk of fracture.
The marginal benefit of conventional calcium-vitamin D supplementation for preserving bone health found in this meta-analysis raises questions about current guideline recommendations yet recommending supplementation in higher-risk populations. More effective and cost-effective pharmacologic strategies beyond bisphosphonates or selective estrogen receptor modulators are needed for the rapidly growing elderly population at risk of incapacitating spontaneous fractures.
The evidence for use of calcium supplements to prevent fracture is well known to be weak, but somehow there are persistent recommendations that everyone, particularly women, need to increase calcium intake. These studies are welcome evidence that physicians can stop recommending calcium supplements.
Interesting meta-analysis suggesting that either dietary calcium or calcium supplements do not appreciably change BMD and are unlikely to have a major effect on fracture outcomes. The authors highlight that they have focused on the outcome of BMD as very few trials included fractures as an outcome. BMD is an imperfect surrogate for fracture. Also, some of these same authors have suggested in previous studies that calcium supplements may increase the risk of adverse cardiovascular outcomes. I'm not sure if I would do anything differently or counsel my patients to do anything differently based on this study, as the meta-analysis is necessarily limited by significant heterogeneity between individual trials. I might suggest older patients with significant constipation or risk of polypharmacy minimize their supplementary calcium, but I have already been doing this for awhile now.
A useful meta-analysis that confirms that increasing calcium intake does indeed increase BMD, and by an amount that makes the BMD like that of a person 1 year younger. The conclusion made by the authors that the fracture risk is minimally impacted cannot really be made from these data. These studies did not look at fracture risk, which depends on more than just BMD; bone quality and trabecular connectivity might be affected, too. Fracture risk reduction by bisphosphonates, for example, is much larger than that expected by the amount of BMD improvement. Making your bones 1 year younger should not be discounted, and may be all that is needed in many older adults. This study also did not address the role of calcium intake in persons taking bisposphonates.
The key question not answered in this review is the combined effect of calcium and vitamin D on fracture rates.
This article about the effect of calcium intake and bone mineral density is very important for both doctors and public.