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The calcium scare--what would Austin Bradford Hill have thought?
B E C Nordin1, J R Lewis, R M Daly
1Endocrine and Metabolic Unit, Royal Adelaide Hospital, North Terrace, Adelaide, SA, 5000, Australia. christopher.nordin@health.sa.gov.au
Insights
Evidence linking calcium supplements to heart attacks is weak and implausible. Further analysis revealed significant limitations in studies, questioning the association. This suggests no change in prescribing habits is needed.
Area of Science:
- Cardiovascular Health
- Nutritional Science
- Epidemiology
Background:
- Concerns exist regarding calcium supplementation's potential link to myocardial infarction (heart attack).
- Existing evidence requires critical evaluation to determine the strength of this association.
Purpose of the Study:
- To rigorously assess the evidence supporting a causal relationship between calcium supplementation and an increased risk of myocardial infarction.
Main Methods:
- Critical appraisal of a meta-analysis involving five prospective trials (8,016 participants).
- Evaluation of related publications and consideration of established criteria for disease causation (e.g., Bradford Hill criteria).
Main Results:
- The meta-analysis exhibited limitations: protocol non-adherence, multiple endpoint testing, and inadequate risk factor data for 65% of participants.
- Key criteria for causation were not met, including biological plausibility, dose-response relationship, consistency, and experimental confirmation.
- Inclusion of a recent trial (1,460 women) yielded a non-significant relative risk of 1.23 (P=0.0695).
Conclusions:
- The current evidence suggesting calcium supplements increase heart attack risk is insufficient to warrant changes in clinical practice.
- The hypothesis of a causal link between calcium supplementation and myocardial infarction remains unsupported by robust scientific data.
Unlabelled:
Detailed consideration of the suggested association between calcium supplementation and heart attacks has revealed weakness in the evidence which make the hypothesis highly implausible.
Introduction:
The aim of this study was to evaluate the strength of the evidence that calcium supplementation increases the risk of myocardial infarction.
Methods:
This study used critical examination of a meta-analysis of the effects of calcium supplements on heart attacks in five prospective trials on 8,016 men and women, and consideration of related publications by the same author.
Results:
The meta-analysis was found to be subject to several limitations including non-adherence to the clinical protocol, multiple endpoint testing and failure to correctly adjust for endpoint ascertainment. The main risk factors for myocardial infarction were not available for 65% of the participants, and none of the trials had cardiovascular disease as its primary endpoint. There were more overweight participants, more subjects on thyroxine and more men on calcium than on placebo. In particular, over 65% of all the heart attacks were self-reported. When the evidence was considered in the light of Austin Bradford Hill's six main criteria for disease causation, it was found not to be biologically plausible or strong or to reflect a dose-response relationship or to be consistent or to reflect the relationship between the trends in calcium supplementation and heart attacks in the community or to have been confirmed by experiment. The addition of a more recent trial on 1,460 women over 5 years reduced the relative risk to 1.23 (P = 0.0695).
Conclusion:
Present evidence that calcium supplementation increases heart attacks is too weak to justify a change in prescribing habits.
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