By Seema Gupta, MD, MSPH
Clinical Assistant Professor, Department of Family and Community Health, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV
SYNOPSIS: Analysis reveals that previous studies demonstrating the health benefits of moderate alcohol drinking were of low quality and that the relatively few published studies meeting the minimal quality criteria to avoid this problem do not show significantly lower mortality risk for moderate alcohol drinkers.
SOURCE: Stockwell T, Zhao J, Clay J, et al. Why do only some cohort studies find health benefits from low volume alcohol use? A systematic review and meta-analysis of study characteristics that may bias mortality risk estimates. J Study Alcohol Drugs 2024;85:441-452.
Past studies have suggested that moderate alcohol drinking may be beneficial for the heart and circulatory system and probably protects against type 2 diabetes.1 However, that may no longer be true — the ground is shifting. An increasing amount of new evidence shows that the health benefits of moderate drinking compared to not drinking may be lacking and, therefore, there may not be a truly safe level of alcohol consumption.2
Recently, the World Health Organization (WHO) released a statement that there is no “safe” level of alcohol consumption that does not affect health.3 And yet, the most current United States dietary guidelines for Americans reflect a recommendation that alcohol consumption be limited to two drinks or less per day for men or one drink or less per day for women.4
In the past, studies often have been flawed because of selection bias and methodology. Some older studies did not consider genetic factors or behaviors such as exercise, diet, or tobacco use. For instance, compared to heavy alcohol drinkers, people who drink moderately might be more likely to exercise, eat healthy, and not smoke. That may have significantly confounded the true effects among people who drink moderately. Additionally, in many older studies, researchers would classify older participants who had given up alcohol because of ill health as drinkers “who consumed less than weekly.”
However, by comparing such “drinkers” to younger, healthier people who drank more regularly, many of these prior studies came to the erroneous conclusion that moderate drinking has health benefits. Thus, it is clear that further research is needed to determine the true health effect of moderate alcohol consumption free from selection biases and methodological flaws.
Stockwell et al identified 107 published cohort studies that followed people over time and looked at the relationship between drinking habits and longevity. By conducting a systematic review with 724 estimates, they explored the relationship between alcohol consumption and all-cause mortality risk for 4,838,825 participants with 425,564 recorded deaths. Further meta-analyses were conducted on subgroups categorized as “lower” or “higher” quality based on potential biases in reference groups classified as abstainers.
Focus was placed on individuals with low-volume (or moderate) alcohol consumption, defined as one to two drinks per day (1.3 g to < 25 g of ethanol).
Potential biases identified included contamination of nondrinking reference groups with former or occasional drinkers, median cohort age, baseline illness, smoking control, alcohol measurement, and socioeconomic status (SES) control.
Researchers found the expected results that studies with younger cohorts and separating former and occasional drinkers from abstainers would have similar mortality risk for low-volume drinkers compared with abstainers (relative risk [RR] = 0.98; 95% confidence interval [CI] 0.87, 1.11). Additionally, studies that did not meet these quality criteria estimated significantly lower risk for low-volume drinkers (RR = 0.84; 95% CI, 0.79, 0.89).
However, when further exploratory analysis was conducted on studies stratified by smoking status, significant differences were observed. Among six studies reporting results for nonsmokers, the RR for low-volume drinkers was 1.16 (95% CI, 0.91, 1.41) when compared with abstainers.
The study authors concluded that biased methodology adopted by several past studies have created in literature the apparent health benefits from moderate or low-volume alcohol drinking.
However, the relatively few published studies that meet minimal quality criteria to avoid this issue have failed to demonstrate significantly lower mortality risk for low-volume drinkers.
Commentary
Past studies on purported health benefits of moderate alcohol use should be a lesson in how positive health impacts can be created just by having studies with consistent methodological and statistical flaws. Beyond the outdated studies, there still is more work to be done in better understanding the true relationship between alcohol use and any perceived or real health benefits. For instance, we must fully evaluate the benefits of diets (i.e., the Mediterranean diet) that contain a glass of red wine as a part of the recommendation.
Similarly, the impact of moderate consumption of red wine and phenolic compounds on reducing inflammation, cholesterol levels, coagulation factors, and insulin sensitivity must be evaluated from a fresh perspective.
However, current research on moderate alcohol consumption also has illuminated some of the health risks, such as the risk of developing gastrointestinal and breast cancer.5 There seems to be no minimal level of alcohol that is protective to the carcinogenic risk. Similarly, no studies have demonstrated the potential existence of a protective effect of alcohol for cardiovascular diseases or type 2 diabetes.
As clinicians, we may be used to the old recommendations when it comes to alcohol consumption for the average population. Perhaps it is time to inform our patients that there is no safe amount of alcohol consumption. Patients should be objectively informed about the risks of cancer and other health conditions associated with alcohol consumption as well as the fact that even moderate drinking may have health risks.
References
- Tanasescu M, Hu FB. Alcohol consumption and risk of coronary heart disease among individuals with type 2 diabetes. Curr Diab Rep 2001;1:187-191.
- Zhao J, Stockwell T, Naimi T, et al. Association between daily alcohol intake and risk of all-cause mortality: A systematic review and meta-analyses. JAMA Netw Open 2023;6:e236185.
- Anderson BO, Berdzuli N, Ilbawi A, et al. Health and cancer risks associated with low levels of alcohol consumption. Lancet Public Health 2023;8:e6-e7.
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th ed. December 2020. https://www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf
- Bagnardi V, Rota M, Botteri E, et al. Alcohol consumption and site-specific cancer risk: A comprehensive dose-response meta-analysis. Br J Cancer 2015;112:580-593.
Analysis reveals that previous studies demonstrating the health benefits of moderate alcohol drinking were of low quality and that the relatively few published studies meeting the minimal quality criteria to avoid this problem do not show significantly lower mortality risk for moderate alcohol drinkers.
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