Study objective: To examine the relationship between smoking and myocardial infarction in women.
Design: Case-control study over 5 years.
Setting: Cases were women admitted to 30 coronary care units in northern Italy. Controls were admitted to the same hospitals with other acute disorders.
Participants: These were 262 young and middle aged women with acute myocardial infarction (median age 49 years, range 24-69) and 519 controls with other acute disorders unrelated to ischaemic heart disease (median age 47 years, range 22-69).
Measurements and main results: Stratification and the Mantel-Haenszel procedure, and unconditional multiple logistic regression were used to obtain relative risks according to levels of cigarette smoking. The regression equations included terms for age, education, coffee and alcohol consumption, diabetes, hypertension, hyperlipidaemia, body mass index and oral contraceptive use. Compared to life long non-smokers, relative risk was not significantly above unity for ex-smokers but among current smokers showed a significant trend to increasing risk with larger numbers of cigarettes smoked, with risk estimates of 2.3, 5.9 and 11.0 for less than 15, 15-24 and greater than or equal to 25 cigarettes per day respectively. Smoking related risks were consistently raised across strata of hyperlipidaemia, hypertension and increased alcohol and coffee intake.
Conclusions: In terms of population attributable risk, about 48% of all myocardial infarctions in young and middle aged Italian women were attributable to cigarette smoking, which is therefore by far the most important preventable determinant of the disease.