Moderate alcohol use and reduced mortality risk: systematic error in prospective studies and new hypotheses.

We have provided recent evidence suggesting that a systematic error may be operating in prospective epidemiological mortality studies that have reported "light" or "moderate" regular use of alcohol to be "protective" against coronary heart disease. Using meta-analysis as a research tool, a hypothesis first suggested by Shaper and colleagues was tested. Shaper et al suggested that people decrease their alcohol consumption as they age and become ill or frail or increase use of medications, some people abstaining from alcohol altogether. If these people are included in the abstainer category in prospective studies, it is reasoned that it is not the absence of alcohol elevating their risk for coronary heart disease (CHD) but, rather, their ill health. Our meta-analytic results indicate that the few studies without this error (i.e., those that did not contaminate the abstainer category with occasional or former drinkers) show abstainers and "light" or "moderate" drinkers to be at equal risk for all-cause and CHD mortality. We explore the history of this hypothesis, examine challenges to our meta-analysis, and discuss options for future research.