No, drinking in moderation does not lengthen your life (even if some studies say so)

The Earth is spherical, tobacco kills and physical exercise is good for your health. Science, in many cases, tends to provide clear and conclusive answers. But there are some more controversial phenomena that show contradictory results in studies and call into question even our common sense. One of them is the impact of alcohol consumption on health: there is no debate about the harmful effects of its abuse, which causes 2.6 million deaths a year in the world and triggers 200 diseases, from cancer to cirrhosis. But there is a slight dilemma regarding its moderate intake. That is, with that glass of wine a day that some studies say not only doesn’t do any harm, but could even be beneficial to one’s health.

First of all, the World Health Organization does not recommend drinking even a drop: “There is no form of alcohol consumption that is risk-free. Even low levels of alcohol consumption carry some risks and can cause harm,” it warns. But there are studies that temper this warning and suggest that moderate consumption by certain groups of people can have protective effects against ischemic heart disease, ischemic stroke or type 2 diabetes, for example. The scientific debate continues and there is research that also casts doubt on such benefits or warns, at least, that the risks continue to outweigh the potential benefits.

The latest, a scientific review published on Thursday in the Journal of Studies on Alcohol and Drugs, delves a little deeper into the research that goes against the grain, and concludes that observational studies showing that moderate alcohol consumption lengthens life are usually flawed: they are biased and of low quality, say its authors.

The researchers, all from Canadian institutions including the Canadian Institute for Substance Use Research, start from the premise that “although many observational studies suggest that people drinking at ‘moderate’ (i.e., low-volume) levels live longer and have fewer illnesses than people assessed as ‘abstainers,’ many potential sources of selection bias contaminate such simple comparisons.” These scientists consider that “assumptions about the validity of the alcohol and health benefit hypothesis have major implications for estimates of the global burden of disease and the formulation of national guidelines on low-risk alcohol use,” and therefore decided to review more than 100 studies on alcohol consumption and mortality from all causes in search of selection biases that led to erroneous conclusions in favor of alcohol consumption.

The meta-analysis identified a handful of characteristics that introduced bias and downplayed the danger of alcohol consumption in the moderate drinkers group (about two glasses of wine a day in men; about half that in women): for example, using older age groups, the presence of former or occasional drinkers within the abstainer group, or including people with other pre-existing health conditions.

The abstainer group

One of the main biases detected was in the definition of the non-drinking cohort, where the lower quality studies group together as abstainers people who have never drunk alcohol at all with others who have consumed alcohol throughout their life, but no longer do so. These unreal profiles of abstainers can distort the results, since they may be people who have, in fact, given up or reduced their alcohol intake for health reasons, warn the authors. “This makes people who continue to drink appear much healthier in comparison,” says scientist Tim Stockwell, the corresponding author of the study, in a statement.

A case in point, which the Canadian scientists note in their article, is that of a large study that estimated the health impact of alcohol and assumed that consuming a certain amount of alcoholic beverages protected against heart disease. According to the authors, this contributed to an estimate of 1.8 million deaths in 2020 associated with alcohol consumption, one million less than the 2016 estimate, which assumed more modest protective effects. This study, published in The Lancet, suggested that people over 40 years of age can benefit from very limited alcohol consumption. The explanation would be that alcohol, due to the ethanol it contains, increases the production of good cholesterol and has an influence on the endothelium that can be beneficial against cardiovascular diseases and diabetes. However, subsequent research pointed out biases, for example, in the group of abstainers, which included people who had stopped or reduced their consumption for health reasons.

Another factor that “creates the false appearance of health benefits from moderate alcohol consumption” is the age of the participants. “As people age, it has been repeatedly shown that those who reduce or completely stop drinking are likely to be in poor health, making those who continue to drink appear healthy by comparison.

The research found that studies less likely to be biased did not find a significant reduction in mortality risk among moderate drinkers. And, in contrast, those studies more likely to be biased “showed apparently substantial health benefits,” the scientists criticized.

The debate continues

The scientific debate is far from over. In Spain, the Predimed study, which analyses the effects of the Mediterranean diet on health, also supports potential health benefits of moderate alcohol consumption. In fact, this particular Mediterranean dietary pattern includes a glass of red wine with lunch, says Miguel Ángel Martínez, professor of Preventive Medicine and Public Health at the University of Navarra and a researcher at Predimed: “When we look at the 14 points of adherence to the Mediterranean diet, one of them is to consume a glass of red wine. If we removed this point, the diet lost part of the cardiovascular protection factor that we saw.” The explanation, he points out, is that any alcohol consumed in moderation increases good cholesterol, improves some coagulation factors, increases insulin sensitivity and, specifically, red wine, has phenolic compounds that reduce inflammation.

Regarding the Canadian study, Martínez rejects its criticism of all observational studies: “I think this outright rebuttal is too bold. Using the same methods, risks are also found in young people.” And he continues: “I am not saying that they are not right. They expressed their doubts. I am conducting doing trials because I do not know.” The epidemiologist is alluding to a study that he has just started to answer a key question: “We want to know what to say to a moderate drinker: to continue or to stop.” The idea is to recruit 10,000 people and assign them to two groups, one that will be persuaded to stop drinking alcohol and another in which they will adapt to the Mediterranean pattern (one or two glasses a day maximum of red wine), to follow them for four years and see what is better. “What public health needs is the best scientific evidence and for alcohol there is none. There are doubts regarding either position. With what we know now, the clear messages we can give are: to those who drink a lot, cut down; to those who don’t drink, don’t start; and to young people under 40, don’t drink because it’s not good for them. And to those who drink a glass of wine a day and are between 50 and 75 years old, we have to try to know what to say to them.”

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