Background: In several observational studies, patients prescribed calcium channel blockers had higher risks of cardiovascular diseases and mortality than those prescribed other antihypertensive medications. We explored these associations in the Nurses' Health Study.
Methods and results: A total of 14 617 women who reported hypertension and regular use of diuretics, beta-blockers, calcium channel blockers, ACE inhibitors, or a combination in 1988 were included in the analyses. Cardiovascular events and deaths were ascertained through May 1, 1994. We documented 234 cases of myocardial infarction. Calcium channel blocker monodrug users had an age-adjusted relative risk (RR) of myocardial infarction of 2.36 (95% CI, 1.43 to 3.91) compared with those prescribed thiazide diuretics. Women prescribed calcium channel blockers had a higher prevalence of ischemic heart disease. After adjustment for these and other coronary risk factors, the RR was 1.64 (95% CI, 0.97 to 2.77). Comparing the use of any calcium channel blocker (monodrug and multidrug users) with that of any other antihypertensive agent, the adjusted RR was 1.42 (95% CI, 1.01 to 2.01). An association between calcium channel blocker use and myocardial infarction was apparent among women who had ever smoked cigarettes (covariate-adjusted RR, 1.81; 95% CI, 1.20 to 2.72) but not among never-smokers (RR, 0.94; 95% CI, 0.48 to 1.84).
Conclusions: In analyses adjusted only for age, we found a significant elevation in RR of total myocardial infarction among women who used calcium channel blockers compared with those who did not. After adjustment for comorbidity and other covariates, the RR was reduced. Whether the remaining observed elevated risk is real, or a result of residual confounding by indication, or chance, or a combination of the above cannot be evaluated with certainty on the basis of these observational data.