In 2019, an article published in The Lancet made headlines when researchers questioned wine’s protective effects against heart disease and instead found that any level of alcohol consumption increased blood pressure and the possibility of a heart attack or stroke. stroke.

But two London-based professors recently delved into these claims and found that the Lancet The study is based on an “unhealthy methodology”.

The 2019 research, conducted by a team from Oxford, recruited more than 500,000 adults from 10 different regions in China and recorded alcohol consumption and the incidence of cardiovascular disease over a 10-year period. The researchers used genetic epidemiological analysis, also known as Mendelian randomization, to examine the data. Genetic epidemiology examines not only who gets sick, but also genetic factors, to try to understand what role genes play and what role environmental factors play (in this case, alcohol consumption).

Many studies have found a J-shaped relationship between alcohol and stroke risk. Non-drinkers had a slightly higher risk of heart attack and stroke, heavy drinkers had a much higher risk that increased with each drink, and moderate drinkers fell to the lower J – they were at the highest risk. weaker.

But the 2019 study authors wrote that after ruling out genetic factors, they found a linear association. The risk of cardiovascular disease increased with each sip of alcohol consumed by the subjects. The study was touted by many as proof that no level of alcohol consumption is safe. “Claims that wine and beer have magical protective effects have not been confirmed,” lead author Richard Peto said in a statement released upon the publication of the research.

Professor Sir Nicholas Wald of University College London and Professor Chris Frost of the London School of Hygiene and Tropical Medicine have previous experience with DNA analysis and were struck by the strong claims of the study. “Professor Wald asked for my opinion on the methodological approach used in the [Lancet] paper because there are links between the approach used by the authors and previous work I had done, ”said Frost Wine spectator.

Wald and Frost dug deeper, and in their new study, published in Oxford’s International Journal of Epidemiology, they write that they discovered a fundamental weakness in the 2019 analysis that masked an underlying J-shaped curve.

Frost and Wald have found in their past genetic epidemiological analyzes that when a relationship between a result and an exposure is not monotonic (such as a J-shaped), there is a risk of systematically skewing the true relationship between the factors. of risk and disease. They performed a hypothetical genetic analysis with results based on the 2019 article and found that non-drinkers had a 15% chance of having a stroke, while light drinkers (one drink per day ) had a 10% chance and heavy drinkers (five drinks per day) had a 20 percent chance. It is a J shape.

How did the Lancet team end up with a linear association? Frost offered an explanation: Suppose people do not drink alcohol, one unit of alcohol per day or two units of alcohol per day, and individuals of these three types have a risk of outcome over a period of time. 15 percent (for those who drink nothing), 10 percent (for those who drink one unit of alcohol per day) and 35 percent (for those who drink two units of alcohol per day). If you form a composite group whose average consumption is one unit of alcohol per day, it is possible that the risk in that group is as low as 10% (if all participants drink one unit per day) or as high as 25%.

The 2019 study authors created such composite groups by separating participants by genotype.

“What we have shown is that when the underlying relationship between an exposure and an outcome is J-shaped, then the type of analysis performed in the 2019 Lancet paper can potentially turn that J-shaped relationship into a linear relationship, ”Frost said.“ We use simple examples to demonstrate this, so I’m confident that could have happened in the 2019 Lancet paper.”

Frost says that further research on Chinese statistical methods and data analyzed in the Lancet paper are needed. “Our work does not prove that moderate alcohol consumption is safe, only that claims that it is harmful are based on flawed methodology.”

“We believe that the scientific position on alcohol consumption and vascular disease is as it was before the publication of the 2019 Lancet paper, ”he added.

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