Current abstainers from alcohol have been identified as an inadequate reference group in epidemiologic studies of the effects of alcohol, because inclusion of former drinkers might lead to overestimation of the protective effects and underestimation of the detrimental effects of drinking alcohol. The authors' objective in the current study was to quantify this association for ischemic heart disease (IHD). Electronic databases were systematically searched for relevant case-control or cohort studies published from 1980 to 2010. Thirty-eight articles fulfilled the inclusion criteria, contributing a total of 5,613 IHD events and 12,097 controls among case-control studies and 1,387 events with combined endpoints and 7,183 events stratified by endpoint among 232,621 persons at risk among cohort studies. Pooled estimates for the subset stratified by sex and endpoint showed a significantly increased risk among former drinkers compared with long-term abstainers for IHD mortality ( among men; relative risk = 1.25, 95% confidence interval: 1.15, 1.36; among women relative risk = 1.54, 95% confidence interval: 1.17, 2.03). For IHD morbidity, the estimates for both sexes were close to unity and not statistically significant. Results were robust in several sensitivity analyses. In future studies, researchers should separate former drinkers from the reference category to obtain unbiased effect estimates. Implications for the overall beneficial and detrimental effects of alcohol consumption on IHD are discussed below.
