Background:
This important public health question was identified by the U.S. Departments of Agriculture (USDA) and Health and Human Services (HHS) to be examined by the 2020 Dietary Guidelines Advisory Committee.
The 2020 Dietary Guidelines Advisory Committee, Beverages and Added Sugars Subcommittee conducted a systematic review to answer this question with support from the Nutrition Evidence Systematic Review (NESR) team.
The goal of this systematic review was to examine the following question: What is the relationship between alcohol consumption and all-cause mortality?
Conclusion statements and grades:
Primary comparisons (among those who currently drink alcohol)
Moderate evidence indicates that higher average alcohol consumption is associated with an increased risk of all-cause mortality compared with lower average alcohol consumption among those who drink. (Grade: Moderate)
Moderate evidence indicates that binge drinking (consuming 5 or more drinks for men or 4 or more drinks for women during a drinking occasion) is associated with increased risk of all-cause mortality, and that more frequent binge drinking is associated with increased risk of all-cause mortality compared with less frequent or no binge drinking among those who drink. (Grade: Moderate)
Secondary comparison (between those who currently drink alcohol and those who have never consumed alcohol)
Limited evidence suggests that low average alcohol consumption, particularly without binge drinking, is associated with a lower risk of all-cause mortality compared with never drinking alcohol. However, in light of the many scientific and public health issues associated with alcoholic beverages, any conclusions about low average consumption compared to never drinking alcohol require careful consideration. (Grade: Limited)
Methods:
A literature search was conducted using 3 databases (PubMed, Cochrane, and Embase) to identify articles that evaluated the intervention or exposure of alcohol consumption and the outcome of all-cause mortality. A manual search was conducted to identify articles that may not have been included in the electronic databases searched. Articles were screened by two NESR analysts independently for inclusion based on pre-determined criteria.
Data extraction and risk of bias assessment were conducted for each included study, and both were checked for accuracy. The Committee qualitatively synthesized the body of evidence to inform development of a conclusion statement(s), and graded the strength of evidence using pre-established criteria for risk of bias, consistency, directness, precision, and generalizability.
Summary of the evidence:
Sixty studies that met the inclusion criteria for this systematic review addressing alcohol consumption and all-cause mortality were identified through the literature search from January 2010 to March 2020.
The body of evidence included one Mendelian randomization study, one retrospective cohort study, and 58 prospective cohort studies. The evidence included no RCTs.
Consistent evidence reported increased all-cause mortality among those with higher average volume of alcohol consumption compared to lower average alcohol consumption. Although consumption categories varied, among those who drank alcohol most studies found lower risk among men consuming within ranges up to 2 drinks per day and women consuming within ranges up to 1 drink per day compared to those consuming higher average amounts. Among studies assessing continuous distributions or based on dose-response relationships among narrower consumption ranges among men who drink, the lowest levels of risk were generally up to 1 or 1.5 drinks on average (depending on how consumption was categorized). Relatively few studies among women examined risk based on categories within the range of up to 1 drink per day on average.
Consistent evidence among those who drink alcohol reported higher all-cause mortality with more frequent binge drinking (consuming 5 or more drinks for men or 4 or more drinks for women during a drinking occasion) compared with less frequent or no binge drinking.
For the secondary comparison between current drinkers and never drinkers, the limited available evidence suggested that low average consumption was associated with lower risk of mortality compared with never drinking status. Included studies were a subset of the 60 studies above that were used to assess the primary comparisons of interest.
Twenty-five studies compared those who consumed alcohol with never drinkers. Approximately half of the studies reported significant findings that low average alcohol consumption (particularly without binge drinking) was associated with reduced risk of all-cause mortality compared with never drinking alcohol, approximately half of the studies indicated no significant relationship, and two studies reported that low alcohol consumption was significantly associated with greater all-cause mortality compared to never drinking alcohol.
Generally, the evidence was limited by inadequate adjustment for confounders, selection bias and limited generalizability (studies often included only middle- and older-aged adults), and potential misclassification or bias from an exposure assessment based on single-time measurements of alcohol consumption. Low average volume was classified variably.
Because the studies provided no consistent definition or categorization of higher average or lower average consumption, these terms are used in a descriptive sense in the conclusion statement. However, across most studies definitions of binge drinking or levels that corresponded to binge drinking were generally consistent; thus binge drinking is defined based on a set number of drinks in the conclusion statement.