The Earth is spherical, tobacco kills and physical exercise is good for health. Science, in many cases, tends to provide clear and conclusive answers. Without a doubt. But there are some more controversial phenomena that show contradictory results in research and call into question even common sense. One of them is the impact of alcohol consumption on health: there is no debate about the harmful effects of the abuse of this substance, which causes 2.6 million deaths a year in the world, and instigator of 200 diseases: from cancer to cirrhosis. But there is a slight dilemma with its moderate intake. That is, with that glass of wine a day to which some research not only does not attribute any harm, but even finds a benefit for health.
First of all, the World Health Organization does not recommend not a drop: “No form of alcohol consumption is free of risk. Even low levels of alcohol consumption carry risks and can cause harm,” he warns. But there are studies that temper this warning and suggest that moderate consumption in certain groups of people can have protective effects against heart disease, stroke or diabetes, for example. The scientific debate continues and there are studies that also cast doubt on such benefits or warn, at least, that the risks continue to outweigh the potential benefits. The latest, a scientific review published this Thursday in the Journal of Studies on Alcohol and Drugsdelves a little deeper into counter-current research and concludes that observational studies that typically show that moderate alcohol consumption prolongs life are often flawed: they are biased and of low quality, its authors say.
The researchers, from the Canadian Institute for Substance Use Research, start from the premise that “although many observational studies suggest that people who drink at ‘moderate’ levels live longer and have fewer diseases than people assessed as abstainers,” there are many biases in the research that can “contaminate” this comparison and the final results. For this reason, the scientists, who consider that these supposed benefits of moderate consumption have “important implications for estimates” of the impact of this substance, decided to analyze more than a hundred studies on alcohol consumption and mortality from all causes in search of those defects that can reorient the balance in favor of alcohol consumption.
The analysis identified a handful of study characteristics that biased risk and downplayed the danger 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, measures of poor-quality alcohol consumption, or including people with other pre-existing health problems.
The teetotallers’ ragbag
One of the main deviations detected is the very construction of the group of non-drinkers, where the lower quality studies group together as abstainers people who have never drunk 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, precisely, given up or reduced their alcohol consumption for health reasons, warn the authors. “This makes people who continue drinking appear much healthier in comparison,” says scientist Tim Stockwell, author of the study, in a statement.
A paradigmatic case, which the Canadian scientists put forward at the outset of their article, is that of a large study that estimated the health impact of alcohol and that used the assumption that consuming a certain amount of alcoholic beverages protected against heart disease. This contributed, according to the authors, to an estimate of 1.8 million deaths in 2020 associated with alcohol consumption, one million less than in the 2016 estimate, which assumed more modest protective effects. This study, published in The Lancetsuggested that people over 40 years of age may 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 activity on the endothelium that may be beneficial against cardiovascular diseases or diabetes. However, further investigations They pointed out biases, for example, in the group of abstainers, which included people who had stopped or reduced 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 authors point out.
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 dilemma is far from reaching a consensus. In Spain, the Predimed intervention study, which analyses the effects of the Mediterranean diet on health, also supports potential benefits The Mediterranean diet is a good source of health benefits from moderate alcohol consumption. In fact, this particular Mediterranean dietary pattern includes a glass of red wine with a meal, says Miguel Ángel Martínez, professor of Preventive Medicine and Public Health at the University of Navarra and 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, in particular, red wine, has phenolic compounds that reduce inflammation.
Regarding the Canadian study, Martínez rejects “the criticism of all observational studies” that they do: “I think this amendment to the whole is 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 express their doubts. I am doing trials because I do not know.” The epidemiologist refers to a research 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,” he summarises. 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, both in one position and in the other. 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.”
Questionable benefits
From a more critical stance regarding the supposed benefits of alcohol, Fernando Rodríguez Artalejo, professor of Public Health at the Autonomous University of Madrid, points out that the defects reported in this new research are “relatively well known.” He himself has participated in an investigation A similar point was also made by the Canadian researchers regarding biases in studies on the potential benefits of alcohol. In their research, Rodríguez Artalejo and his team concluded that light or moderate alcohol consumption in people over 60 years of age “does not seem to have any statistically significant benefit on mortality compared to abstaining from alcohol”, but rather the opposite. “This article shows that in studies that are carried out with the most methodological rigor, no benefits of consuming alcohol are observed”.
Rodríguez Artalejo points out that “the controversial issue is whether drinking a little is good for your health, has no effect or is bad”, but admits that the dilemma is “difficult to resolve”. “It is a debate, moreover, with little relevance for the vast majority of people. Because a little can do you neither much harm nor much benefit. It is possible that there is a small cardiovascular benefit, but we always talk about small effects. And what we do know is that for cancer, the risk increases from the first drop”, he agrees. The epidemiologist calls for caution with the messages that are sent to the public: “We should never promote alcohol for health reasons. If it has a cardiovascular effect, we can also achieve that with other healthy lifestyle habits or more appropriate treatments. And people have to know that to benefit from the Mediterranean diet or another healthy diet, it is not necessary to drink alcohol”.
For his part, Iñaki Galán, a scientist at the National Epidemiology Centre of the Carlos III Health Institute, said in statements to the scientific portal SMC Spain, The methodological approach of this research is “appropriate for the objectives set”: “The message that reducing the amount of alcohol consumed can have beneficial effects on health has been built on weak scientific evidence,” says the scientist, who did not participate in this research. Galán has directed a mega-study that concluded that there is no moderate use of alcohol without risk: “This article addresses the multiple biases that observational cohort studies have in the association of alcohol consumption and mortality. The conclusion is the enormous variation in the results on which this message is based, observing that when selecting young cohorts and separating ex-drinkers and occasional drinkers from abstainers, the risk of mortality in consumers of low amounts of alcohol was very similar,” he emphasizes.
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