Calcium intake and bone mineral density: systematic review and meta-analysis
BMJ 2015; 351 (Published 29 September 2015)

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.

In summary, increasing calcium intake from dietary sources increases BMD by a similar amount to increases in BMD from calcium supplements. In each case, the increases are small (1-2%) and non-progressive, with little further effect on BMD after a year. Subgroup analyses do not suggest greater benefits of increasing calcium intake on BMD in any subpopulation based on clinically relevant baseline characteristics. The small effects on BMD are unlikely to translate into clinically meaningful reductions in fractures. Therefore, for most individuals concerned about their bone density, increasing calcium intake is unlikely to be beneficial.

What is already known on this topic

Older people are recommended to take at least 1000-1200 mg/day of calcium to treat and prevent osteoporosis
Many people take calcium supplements to meet these recommendations
Recent concerns about the safety of such supplements have led experts to recommend increasing calcium intake through food rather than by taking supplements, but the effect of increasing dietary calcium intake on bone health is not known

What this study adds

Increasing calcium intake either by dietary sources or supplements has small non-progressive effects on bone density
These effects are unlikely to translate into clinically meaningful reductions in fractures

G Mohan.