Background: Studies on the association between alcohol consumption and myocardial infarction (MI) have typically used baseline data on alcohol consumption and potential confounders. This study aimed at investigating the association between alcohol consumption and MI considering time-varying alcohol consumption and time-varying confounders.
Methods: Data were available for 1030 males participating in the Kuopio Ischaemic Heart Disease Risk Factor Study (Finland). Baseline data for the present study were collected in 1991-93. MIs were ascertained from national registries until December 2005. Alcohol consumption was categorized into four groups. Data were analysed using conventional discrete-time hazard and marginal structural models (MSMs). Time-invariant covariates were age, working status, diabetes and cigarette-years. Time-varying covariates in the MSM were prior alcohol consumption, smoking, history of cardiovascular diseases, body mass index, high-density lipoprotein cholesterol, systolic blood pressure, insulin and fibrinogen.
Results: An insignificant increase of MI risk among the heaviest alcohol consumers (≥168 g week(-1)) compared with the reference group (12-83 g week(-1)) was observed when using a conventional model including baseline alcohol consumption and confounders measured prior to baseline [relative risk (RR) = 1.20, 95% confidence interval (95% CI) = 0.68-2.12]. When using a conventional model with time-varying alcohol consumption and adjusting for prior confounders, an increased risk of MI among the heaviest alcohol consumers was revealed (RR = 1.71, 95% CI = 1.03-2.85). There was also a trend towards increased risk among the heaviest consumers using the MSM (RR = 1.59, 95% CI = 0.93-2.72).
Conclusion: Our findings suggest that standard methods using only baseline data on alcohol consumption and confounders may lead to biased estimates on the association between alcohol consumption and MI.