Discussions about the dietary supplements are often far too general to be truly useful, in my view. For a meaningful debate, we need to define what supplement we are talking about and make clear what condition it is used for. A recent paper meets these criteria well and is therefore worth a mention.
The review was aimed at addressing the controversy regarding the optimal intake, and the role of calcium supplements in the treatment and prevention of osteoporosis. The authors demonstrate that most studies on the subject show little evidence of a relationship between calcium intake and bone density, or the rate of bone loss. Re-analysis of data from the placebo group from the Auckland Calcium Study demonstrates no relationship between dietary calcium intake and rate of bone loss over 5 years in healthy older women with intakes varying from <400 to >1500 mg per day .
The authors argue that supplements are therefore not needed within this range of intakes to compensate for a demonstrable dietary deficiency, but might be acting as weak anti-resorptive agents via effects on parathyroid hormone and calcitonin. Consistent with this, supplements do acutely reduce bone resorption and produce small short-term effects on bone density, without evidence of a cumulative density benefit. As a result, anti-fracture efficacy remains unproven, with no evidence to support hip fracture prevention (other than in a cohort with severe vitamin D deficiency) and total fracture numbers are reduced by 0-10%, depending on which meta-analysis is considered. Five recent large studies have failed to demonstrate fracture prevention in their primary analyses.
These facts, the authors argue, must be balanced against the possible harm. The risks of regularly taking calcium supplements include an increase in gastrointestinal side effects (including a doubling of hospital admissions for these problems), a 17% increase in renal calculi and a 20-40% increase in risk of myocardial infarction. Each of these adverse events alone neutralizes any possible benefit in fracture prevention.
The authors draw the following detailed conclusions: “Concern regarding the safety of calcium supplements has led to recommendations that dietary calcium should be the primary source, and supplements reserved only for those who are unable to achieve an adequate dietary intake. The current recommendations for intakes of 1000–1200 mg day−1 are not firmly based on evidence. The longitudinal bone densitometry studies reviewed here, together with the new data included in this review relating to total body calcium, suggest that intakes in women consuming only half these quantities are satisfactory and thus, they do not require additional supplementation. The continuing preoccupation with calcium nutrition has its origin in a period when calcium balance was the only technique available to assess dietary or other therapeutic effects on bone health. We now have persuasive evidence from direct measurements of changes in bone density that calcium balance does not reflect bone balance. Bone balance is determined by the relative activities of bone formation and bone resorption, both of which are cellular processes. The mineralization of newly formed bone utilizes calcium as a substrate, but there is no suggestion that provision of excess substrate has any positive effect on either bone formation or subsequent mineralization.
Based on the evidence reviewed here, it seems sensible to maintain calcium intakes in the region of 500–1000 mg day−1 in older individuals at risk of osteoporosis, but there seems to be little need for calcium supplements except in individuals with major malabsorption problems or substantial abnormalities of calcium metabolism. Because of their formulation, costs and probable safety issues, calcium supplements should be regarded as pharmaceutical agents rather than as part of a standard diet. As such, they do not meet the standard cost–benefit criteria for pharmaceutical use and are not cost-effective. If an individual’s fracture risk is sufficient to require pharmaceutical intervention, then safer and more effective measures are available which have been subjected to rigorous clinical trials and careful cost–benefit analyses. Calcium supplements have very little role to play in the prevention or treatment of osteoporosis.”
Clear and useful words indeed! I wish there were more articles like this in the never-ending discussion about the complex subject of dietary supplements.