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Alcohol and coronary heart disease risk - is there an unknown confounder?
Researchers from Finland have carried out a population-based cross-sectional study to evaluate whether confounding by several known or suspected coronary heart disease risk factors are likely to explain the lower coronary heart disease risk among light alcohol drinkers compared with never-drinkers. Data on 41,099 participants (6,222 men, 34,877 women) were derived from two ongoing cohort studies, the “10-Town Study” and “Finnish Hospital Personnel Study,” in Finland in 2000-02. Hypertension, body mass index (BMI), diabetes, depression, sleep disturbances, smoking, physical activity, life satisfaction, psychological distress, trait anxiety, independent and dependent life events, length of working hours, job control, job strain and effort reward imbalance were compared between never-drinkers and light drinkers (<70 g of alcohol per week).

Of the 16 comparisons under study, seven showed significant differences between never-drinkers and light drinkers. Five of the differences favored never drinkers and two showed a disadvantage. The latter were low BMI and low leisure-time physical activity, both more common among never-drinkers than among light drinkers. In contrast, smoking, sleep disturbances, trait anxiety, effort reward imbalance and dependent life events were less common among never-drinkers than among light drinkers. The investigators concluded, “None of the risk factors studied was a likely candidate for an unknown confounder.”

Curtis Ellson comments: This is an interesting analysis to deal with the oft-quoted suggestion that associated lifestyle factors and cardiovascular risk factors are more favorable in moderate drinkers than in abstainers, and these factors (and not alcohol) are the reasons for less coronary disease among drinkers. This paper investigated the prevalence of a large number of lifestyle factors that have been suggested as increasing or decreasing the risk of coronary disease. Included were a number of psychological and behavioral factors that are often not included as “risk factors” and adjusted for in epidemiologic studies. These included depression, sleep disturbances, life satisfaction, psychological distress, trait anxiety, independent and dependent life events, length of working hours, job control, job strain and effort reward imbalance.

In these analyses, many factors considered to be protective against coronary disease were more common in abstainers, indicating that such factors could not explain lower heart disease rates among drinkers. However, since the relation between each of these factors, or alcohol consumption itself, are not reported in this paper, we cannot judge the extent to which such factors might relate to heart disease in this study population. Further, this is a cross-sectional study, and there is always the possibility that subjects who had developed heart disease had modified their lifestyle habits, and prospective studies are needed. Still, this analysis tends to support the hypothesis that alcohol itself is the cause of the lower risk of coronary disease seen routinely among moderate drinkers.

Article:Poikolainen K, Vahtera J, Virtanen M, Kivimaki M. Alcohol and coronary heart disease risk - is there an unknown confounder? Addiction 2005;100:1150-1157.

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