Meta-analyses question calcium's efficacy for boosting bone health & reducing fractures

Osteoporosis has been described as a silent killer, and recent data from the National Osteoporosis Foundation showed that approximately 9 million American adults currently have osteoporosis and another 48 million have low bone mass, placing them at increased risk. Older women are at a greater risk than other population groups, prompting recommendations to increase calcium intakes from the diet and supplements.

Papers published in the British Medical Journal​ concluded that dietary and supplemental calcium may produce small (1-2%) increases in bone mineral density (which "are unlikely to lead to a clinically meaningful reduction in risk of fracture"​), and that dietary calcium was not associated with risk of fracture.

In an accompanying editorial in the BMJ​, Prof Karl Michaelsson from Uppsala University in Sweden wrote: “[C]alcium and vitamin D supplements have been marketed well beyond the […] target population of older women in residential care with low calcium intake and low vitamin D concentration.​

“By use of guidelines such as those by NOF and the International Osteoporosis Foundation (IOF), marketing now extends to all older people with dietary intakes below the recommended 1200 mg calcium and 800-1000 IU vitamin D daily. By this definition virtually the whole population aged over 50 is at risk. Most will not benefit from increasing their intakes,” ​added Prof Michaelsson

‘Americans are not getting enough calcium from diet alone’​

Commenting on the two meta-analyses, Duffy MacKay, ND, Sr VP of scientific and regulatory affairs at the Council for Responsible Nutrition (CRN), said: “Calcium is needed at every life stage for a variety of health reasons, including maintaining strong bone health. Despite the headline in the accompanying editorial, these two meta-analyses do, in fact, suggest positive results for calcium supplements and bone health, albeit ‘weak positive’ as the authors refer to the benefits. ​

“However, by conducting meta-analyses, the authors combine data from numerous studies and it is the combination of data that steer the direction of the results. In this case, the inclusion of data from the calcium and vitamin D arm of the Women’s Health Initiative (WHI), a study with widely-acknowledged limitations, heavily skewed the results of the meta-analyses toward ‘weak positive.’ Whereas, had the meta-analyses included data from the re-analysis of the WHI, which demonstrated a significant reduction in fracture risks, the results of the meta-analyses could have gone from ‘weak positive’ to strong positive.​

“As importantly, government data and the scientific report from the upcoming Dietary Guidelines for Americans have identified that Americans are not getting enough calcium from diet alone. Supplementing with calcium is a safe and beneficial avenue to address this issue of nutrient shortfalls in the American population.”​

WHI​

The WHI was the largest randomized, double-blind, placebo-controlled clinical trial of these nutrients, and involved 36,282 postmenopausal women in the US. The women were randomly assigned to receive to 1,000 mg elemental calcium carbonate plus 400 IU of vitamin D3 daily or placebo for an average if seven years.

The initial analysis of the data, published in 2006 in the New England Journal of Medicine​ (Vol. 354, pp. 669-683), concluded: “Among healthy postmenopausal women, calcium with vitamin D supplementation resulted in a small but significant improvement in hip bone density, and did not significantly reduce hip fracture.”​

However, in the 59% of the participants who actually adhered to the supplementation program (assuming 80% or more compliance with taking the supplements) the number of fractures was 29% lower (Calcium/ vitamin D supplements good for bones – if you take them​​; NutraIngredients-USA, ​Feb 16, 2006).

Hip fracture benefits​

The re-analysis mentioned by Dr MacKay was published in Osteoporosis International​​ (2013, Vol. 24, pp 567-580), and found that, among women not taking calcium or vitamin D supplements at the start of the study, the risk of hip fracture occurrence was 38% lower, compared to the placebo group.

In addition, when data from the WHI clinical trial and the WHI prospective observational study were combined, the risk was 35% lower.

New meta-analyses​

The new analyses, performed by researchers at the University of Auckland and the University of Otago in New Zealand, pooled data from randomized controlled trials and observational studies of extra dietary or supplemental calcium in women and men aged over 50. Study design and quality were taken into account to minimize bias, they note.

In the first analysis, they found that increasing calcium intake from dietary sources or by taking supplements produces small (1-2%) increases in bone mineral density.

“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,”​ they concluded.

In the second analysis, they found that dietary calcium intake is not associated with risk of fracture, and there is no clinical trial evidence that increasing calcium intake from dietary sources prevents fractures.

“Calcium supplements have small inconsistent benefits on fracture reduction but probably have an unfavourable [sic] risk:benefit profile,”​ they wrote. “There was no risk reduction in fracture at any site in pooled analyses of the randomised [sic] controlled trials of calcium supplements at lowest risk of bias, and there was evidence of publication bias in small-moderate sized trials. ​

“Collectively, these results suggest that clinicians, advocacy organisations [sic], and health policymakers should not recommend increasing calcium intake for fracture prevention, either with calcium supplements or through dietary sources.”​

Sources:​
British Medical Journal​
2015; 351:h4580, doi: 10.1136/bmj.h4580
“Calcium intake and risk of fracture: systematic review”​​
Authors: M.J. Bolland

British Medical Journal​
2015; 351:h4183, doi: 10.1136/bmj.h4183
“Calcium intake and bone mineral density: systematic review and meta-analysis”​​
Authors: V. Tai, W. Leung, et al.

British Medical Journal​
2015; 351:h4825, doi: 10.1136/bmj.h4825
Editorial: “Calcium supplements do not prevent fractures. Revisit recommendations to increase intake beyond a normal balanced diet”​​
Author: K. Michaelsson