Risk of myocardial infarction in young female smokers

Objectives - To determine the extent of risk of myocardial infarction from cigarette smoking in young women, and to examine the relation of smoking with other putative risk factors. Design - Community based case control study. Setting - England, Scotland, and Wales. Patients - Women (n = 448) between 16 and 44 years old with a diagnosis of incident myocardial infarction between 1 October 1993 and 16 October 1995. Controls (n = 1728) were age and general practice matched women without a diagnosis of myocardial infarction. Outcomes measures - Odds ratios for risk of myocardial infarction associated with smoking and other risk factors. Results - Odds ratios for myocardial infarction in smokers versus non-smokers showed a strong dose response, from 2.47 (95% confidence interval (CI) 1.12 to 5.45) in smokers of 1-5 cigarettes per day to 74.6 (95% CI 33.0 to 169) in smokers of ≥ 40 cigarettes per day. There was no interaction of smoking with use of oral contraceptives, but there were additive risks with other clinical risk factors such as hypertension and diabetes. It is estimated that if all women aged 16-44 years were able to stop smoking, 400 cases of myocardial infarction per annum (of whom 112 would die) would be prevented. Conclusions - In young women the risk of myocardial infarction from smoking was considerable, and heavy smokers with other risk factors were especially at risk.