MYOCARDIAL INFARCTION AND OVERALL CORONARY HEART DISEASE
The scientific evidence for a link between coffee drinking or caffeine intake and coronary heart disease risk is entirely derived from observational epidemiological studies. Such studies can only show associations and not cause effect relationships. There are no intervention trials on the relationship between coffee drinking or caffeine intake and coronary heart disease risk and hence no cause effect studies although there are intervention trials on risk factors for disease such as blood pressure, blood lipids and blood homocysteine.
Two types of observational epidemiological study have been published. The case control study has the weakest design as exposure, in this case to caffeine or coffee, is measured at the same time as coronary heart disease risk making it impossible to decide which is cause and which effect. The cohort study has a stronger design as exposure is measured prospectively in a group of initially healthy subjects and the appearance of coronary heart disease over time monitored.
Case control studies and cohort studies are subject to confounding and the best studies adjust the data for other known risk factors for coronary heart disease. However, even after adjustment it is still possible that coffee drinking or caffeine intake are acting as markers for some other aspect of lifestyle which is the true cause of the disease. A good example of this is the finding of the Olivetti Heart Study that after multivariate adjustment coffee consumption was significantly associated with cigarette smoking, a well-established risk factor for heart disease (1). The idea that coffee drinking is a marker for a lifestyle characterised by known risk factors for heart disease including smoking, lack of physical activity and consumption of saturated fat is supported by data from three other cohort studies (2, 3, 4).
St. Petersburg, Florida, USA
Henderson, Nevada, USA
City of Ryde, Australia,
Vanuatu, Port Vila,
Korea (North), Pyongyang