To evaluate the effect of tobacco smoking on the risk of non-fatal acute myocardial infarction in young adults (≤45 years), and whether there is modification of this effect by sex.

We conducted a population-based case-control study with 329 incident acute myocardial infarction cases (42 women; 287 men), consecutively admitted to the Cardiology department of hospitals in Porto, Portugal, and 778 controls (486 women; 292 men), selected within the non-institutionalized Porto population, during 2001–2003. Odds ratios and 95% confidence intervals (OR, 95%CI) were calculated using unconditional logistic regression.

The prevalence of current smoking was 80.8% in male cases and 53.8% in male controls (OR=3.63, 95%CI: 2.50, 5.27) and 59.5% of female cases were smokers compared to 35.8% of controls (OR=2.64, 95%CI: 1.39, 5.02). No interaction was found between current smoking and sex on myocardial infarction risk (p=0.401). A dose–effect response was present, the odds favoring myocardial infarction reaching an eight-fold increase for those that smoked >25 cigarettes/day compared to never smokers. The risk estimate for former smokers was similar to never smokers.

Tobacco smoking is an important independent risk factor for acute myocardial infarction in young adults, with similar strength of association for both sexes.