Adverse events from calcium supplementation: relationship to errors in myocardial infarction self-reporting in randomized controlled trials of calcium supplementation

The clinical effects of calcium supplements on adverse events reporting have not been well described. This study reviews randomized controlled trial (RCT) evidence of adverse events to clarify the epidemiology of these events. The hypothesis that patient self-report of myocardial infarction (MI) is increased in individuals receiving calcium supplementation is because of an increase in non-MI events incorrectly perceived by the patient as being because of MI, is examined. In seven RCTs summary self-reported gastrointestinal (GI) adverse event rates were more common in participants receiving calcium. These were described as constipation, excessive abdominal cramping, bloating, upper GI events, GI disease, GI symptoms, and severe diarrhoea or abdominal pain (calcium 14.1%, placebo 10.0%), relative risk (RR) 1.43 95% confidence interval (CI) 1.28 to 1.59, p < 0.001. Adjudicated functional GI hospitalizations in one study were calcium 6.8%, placebo 3.6% (RR 1.92, 95% CI 1.21-3.05, p = 0.006). Direct comparison of self-reported and adjudicated MI events in the two trials of dietary calcium supplementation showed self-reported MI rates of 3.6% in the calcium group and 2.1% in the placebo group. After adjudication the MI rates were 2.4% in the calcium group and 1.6% in the placebo group (RR 1.45, 95% CI 0.88-2.45, p = 0.145). These data support the hypothesis that calcium tablets increase the incidence of adverse GI events, which may account for an increase in self-reported MI in calcium treated patients but not controls.