Risk factors for acute myocardial infarction in Copenhagen II: Smoking, alcohol intake, physical activity, obesity, oral contraception, diabetes, lipids, and blood pressure

The Copenhagen City Heart Study is a prospective cardiovascular population study designed to evaluate incidence of, and risk factors for, cardiovascular disease. A random sample, comprising approximately 20,000 people, were invited to participate. Initial information about potential risk factors was collected during 1976-78 (attendance rate 74%); data about 389 new cases of first acute myocardial infarction (AMI) was obtained from a second survey in 1981-83, as well as from hospital and death registers up to 31 December 1983. The average observation period was 6.5 years. Cox's regression model was used for data analysis. Some 'basic' factors, namely age, sex, family history of AMI, early parental death, height, earlobe crease, length of school education, income and living alone or with a partner were dealt with in a previous paper and are among the potential risk factors for AMI included in the Copenhagen City Heart Study. In this analysis we also include life-style characteristics, some biological traits and disease conditions. An increased risk for first AMI among smokers was graded: the estimated relative risk (ERR) for heavy smokers consuming more than 29g tobacco per day was 2.8 relative to non-smokers. Alcohol intake of five or more drinks per day was associated with a decreased risk, an ERR of 0.6 relative to those who did not drink alcohol daily. Physical inactivity during work but not at leisure was associated with increased risk (ERR 1.4) as was body mass index where the risk was mediated mainly through blood pressure and plasma triglycerides. Oral contraception was not associated with an increased risk, whereas with diabetes the risk increased (the ERR for diabetes being 1.8). Plasma cholesterol above the level of approximately 7 mmol l-1 proportionally increased risk; the ERR in the 1.5% with the highest level was 3.7. A low triglyceride level was associated with low risk; the ERR in the fifth of the study population with the lowest level was 0.6. Elevated blood pressure also proportionally increased risk. Subjects on antihypertensive drug treatment had higher risk than non-treated subjects with similar blood pressure. The effect of socioeconomic factors described in the previous paper was not mediated through their influence on the risk factors included in the present analysis.