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Editorials

Calcium supplements do not prevent fractures

BMJ 2015; 351 doi: https://doi.org/10.1136/bmj.h4825 (Published 29 September 2015) Cite this as: BMJ 2015;351:h4825
  1. Karl Michaëlsson, professor
  1. 1Department of Surgical Sciences, Uppsala University, 751 85 Uppsala, Sweden
  1. Correspondence: karl.michaelsson{at}surgsci.uu.se

Revisit recommendations to increase intake beyond a normal balanced diet

Calcium is vital to many biological processes, and serum concentration is tightly regulated. Net calcium excretion must be replaced, but the amount of calcium needed has been debated for decades. Twenty five years ago in this journal, Kanis and Passmore concluded that calcium supplements to prevent fractures were not justified by the available evidence,1 though this view was challenged by determined opponents. According to two linked articles,2 3 the conclusions of Kanis and Passmore still hold true. Furthermore, there seems little to be gained from an increased consumption of calcium rich foods.

In the first paper, Tai and colleagues (doi:10.1136/bmj.h4183) report a systematic review and meta-analysis of randomised controlled trials of extra dietary or supplemental calcium in women and men aged over 50.2 They found a meagre increase in bone mineral density, with no further gains beyond the first year. Importantly, this limited improvement was no greater when calcium was combined with vitamin D at any dose, even among participants with low serum concentration of 25-hydroxyvitamin D (25-OH-D), a high calcium dose, or baseline dietary calcium intake <800 mg/day.

In the second paper, Bolland and colleagues (doi:10.1136/bmj.h4580) explored whether increased calcium intake could reduce the risk of fractures.3 Most of the trials in this review tested supplements, and the authors identified evidence of publication bias in small or moderate sized trials. Meta-analyses confined to trials at lowest risk of bias found that calcium supplements had no effect on risk of fractures at any site. A clear exception was the classic French study by Chapuy and colleagues, performed in women living in nursing homes with a mean age of 84 who had the combination of a habitual low calcium intake (500 mg/day), very low serum concentrations of vitamin D (20 nmol/L), and, importantly, also low serum concentrations of calcium.3 4

Evidence on dietary calcium came mostly from observational cohort studies, too heterogeneous to be pooled in a meta-analysis.3 The studies differed in size, the quality of dietary assessments, range of exposures, adjustments for energy intake, selection of covariates, and ascertainment of fractures (self report versus identification from registers). Nonetheless, Bolland and colleagues found little evidence to support the theory that higher intake of dietary calcium could reduce risk of fractures.3

A very low calcium intake might lead to rickets and osteomalacia when serum vitamin D concentrations are only moderately low, while very low vitamin D concentrations will not necessarily lead to these conditions if calcium intake is adequate.5 This interplay between vitamin D status and calcium intake is probably just as important in the prevention of fractures. Identifying the optimum interdependent thresholds for both would be a substantial clinical advance that could help to target interventions and potentially cut costs. Overemphasis on high intakes of calcium without firm scientific evidence has probably hindered development in this research area.

A large scale meta-analysis of individual patient data from high quality trials could be one way to quantify the effects of extra calcium from diet or supplements at different thresholds of vitamin D concentration, baseline dietary calcium intake, or serum calcium concentration. We should also evaluate possible effects of different dairy products6 and the potential impact of other nutrients and foods on risk of fracture.7 The evidence currently available, however, gives us a strong signal that calcium supplements with or without vitamin D do not protect older people in general from fractures. This view is shared by the United States Preventive Services Task Force after their recent meta-analysis.8 Calcium supplementation alone might even increase the risk of hip fracture, the most devastating type of fragility fracture.3 9

The official recommendations in the UK and Nordic countries of 700-800 mg/day of dietary calcium for adults seem at present to be enough. This intake can be achieved with a normal varied diet. Other guidelines such as from the US National Osteoporosis Foundation (NOF; http://nof.org/calcium) promote at least 1200 mg calcium and 800-1000 IU vitamin D daily as a goal for women aged 50 or older. Few women can achieve these intakes through dietary means alone.10 11 As a result, most middle aged and older women in the US now take calcium and vitamin D supplements. As there is currently little, if any, firm evidence that higher intakes prevent bone loss, falls, or fractures in middle aged and older women and men living in the community,2 3 10 11 12 13 the continued emphasis by several organisations (such as NOF) on ever increasing intakes of calcium and vitamin D is puzzling.

The profitability of the global supplements industry probably plays its part, encouraged by key opinion leaders from the academic and research communities.14 Manufacturers have deep pockets, and there is a tendency for research efforts to follow the money (with accompanying academic prestige), rather than a path defined only by the needs of patients and the public. The research agenda and recommendations can also be influenced by the conflicts of interest that arise when leading academics have shares or management positions in companies making and marketing supplements.

While the study by Chapuy and colleagues has been influential,9 calcium and vitamin D supplements have been marketed well beyond the trial’s 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.10 11 Most will not benefit from increasing their intakes2 3 10 11 12 13 and will be exposed instead to a higher risk of adverse events such as constipation, cardiovascular events, kidney stones, or admission for acute gastrointestinal symptoms.3 The weight of evidence against such mass medication of older people is now compelling, and it is surely time to reconsider these controversial recommendations.

Notes

Cite this as: BMJ 2015;351:h4825

Footnotes

References

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