The authors report on data collected in the INTERHEART Study, a large international collaborative project of individuals with a first myocardial infarction (MI) and age- and sex-matched controls from 52 countries in Asia, Europe, the Middle East, Africa, Australia, North and South America. Included were nations with very divergent lifestyles, religions, degrees of development, and drinking habits. The authors attempted to provide a “world-wide” overview of the relation of alcohol consumption to the risk of myocardial infarction (MI). However, they were forced to use a case-control design, a type of study with many opportunities for bias and one that prevents determination of a causal relation. Further, the lack of detailed data on the amount of alcohol consumed by individuals weakens their results. While the authors state that their study shows that low levels of alcohol use are associated with a moderate reduction in the risk of MI, they point out differences in results in different countries. Forum members considered that these large differences severely limit their ability to use such a dataset to provide overall conclusions on alcohol and MI. For example, only 1% of the non-drinkers in this study came from W. Europe and 1% from North America, while more than 70% of the non-drinkers came from the Middle East or Asia. With such diversity (e.g., almost all the abstainers were from one area), it is not possible to adequately “adjust” for such regional differences in analysis. The authors also studied how alcohol consumption shortly prior to (in the 24 hours before) the occurrence of a MI relate to the short-term risk of MI. While their results show an increased risk for heavy drinking immediately prior to an MI (a result that differs from that of some previous studies), they admit analytic problems, stating: “Thus there remains uncertainty over the risk of MI in the period immediately following alcohol intake.”
Previous large prospective cohort studies (a type of epidemiologic study that decreases the risk of recall bias regarding alcohol intake and certain types of confounding) have clearly shown an inverse relation between moderate alcohol consumption and MI. Most of the previous studies have provided much more detailed data on alcohol exposure than did the present study. The authors realized many of these problems, and warn against using their results to make overall conclusions about the association between alcohol and MI from their paper. They state: “The associations observed between alcohol use and MI may be accounted for by unmeasured confounders such as genetic differences between populations, variation in alcohol type or preparation, and heterogeneity of social context. The present analysis should therefore prompt further research to clarify the nature of the association between alcohol use and MI.” Unfortunately, the conclusions presented in the abstract and in the do not mention such problems.
Some Forum members worried that many readers of the paper will be left with a very misleading impression of the relation of alcohol consumption to myocardial infarction, and will not be aware that the conclusions trumpeted in the abstract are compromised by weak data. Overall, members considered that the present paper adds little to our knowledge about the risks and benefits of alcohol in relation to cardiovascular disease.
Reference: Leong DP, Smyth A. Teo KK, McKee M, Rangarajan S, Pais P, Liu L, Yusuf S, on behalf of the INTERHEART investigators. Patterns of Alcohol Consumption and Myocardial Infarction Risk: Observations from 52 Countries in the INTERHEART Case-Control Study. Circulation 2014 (pre-publication) DOI: 10.1161/CIRCULATIONAHA.113.007627.