A low level of alcohol consumption does not protect against stroke, new research suggests, in the latest blow to the idea that a few drinks can be beneficial to health.
At least 100,000 people have strokes in the UK every year, according to recent figures. It had been thought that low levels of alcohol consumption might have a protective effect against stroke, as well as other diseases and conditions. Now researchers say that in the case of stroke, even low levels of alcohol consumption are bad news.
“Moderate drinking of about one or two drinks a day does not protect against stroke,” said Dr Iona Millwood, co-author of the study from the University of Oxford.
The results chime with a major study released last year which concluded there is no healthy level of drinking.
Writing in the Lancet, researchers from the UK and China described how they examined the impact of alcohol on stroke using a type of natural experiment.
About a third of people from east Asia have genetic variants that affect the way alcohol is broken down in the body, which can make drinking an unpleasant experience and lead to flushed skin.
People with these genetic variants are known to drink less – a situation confirmed by the latest study – but who has these genetic variants is random, meaning they can appear in people regardless of their social situation or health. As a result, the team were able to look at the impact of drinking on the risk of stroke without many of the other issues that can muddy the waters.
The team drew on health, lifestyle and genetic data collected from more than half a million adults in China between 2004 and 2008. Participants were followed until the start of 2017 and the team looked at the occurrence of conditions including heart attack and stroke from medical records.
Only 2% of women in the study said they consumed alcohol most weeks, compared with 33% of men.
At first glance, the results appeared to find a protective effect against stroke for those drinking about 100g of alcohol a week – about four large glasses of wine.
After using genetic data from a smaller group of participants and taking into account where they lived to predict the amount of alcohol men were consuming, researchers found no protective effect from moderate drinking. Instead, for every additional 280g of alcohol consumed per week, the total stroke risk was raised by 38%.
“One or two drinks a day is increasing stroke risk by about 10-15%,” said Prof Sir Richard Peto, another author of the study.
When the team looked at the situation in women, who drink very little for cultural reasons, they found no link between their genetic variants and their risk of stroke. The team says this backs up the conclusion that it is alcohol consumption that is behind the link to stroke risk seen in men.
The authors say this means previous signs of an increased risk of stroke at low alcohol consumption are not down to moderate drinking offering protection, but rather that there are differences between moderate and non-drinkers that muddy the waters – for example people already in poorer health might not drink.
The study has limitations, including that intake was based on self-reporting and the fact that most alcohol consumed was spirits, while some have suggested wine contains other components that could be beneficial for health.
David Spiegelhalter, Winton professor for the public understanding of risk at the University of Cambridge, and who was not involved in the study, said the new study was convincing.
“This is a very impressive study which shows that men who, by chance, have a combination of genes that put them off drinking alcohol have a lower risk of stroke compared with those without these genes,” he said.
“The fact that this is not true for Chinese women, who tend not to drink whatever their genes, suggests this effect is due to the alcohol rather than the genes themselves. I have always been reasonably convinced that moderate alcohol consumption was protective for cardiovascular disease, but now I am having my doubts.”
Tim Chico, professor of cardiovascular medicine at the University of Sheffield, said whether the increased risk of stroke from drinking makes a meaningful difference to people will depend on their underlying risk – which is based on their age, weight, whether they smoke and other factors. But, he added: “Unfortunately, when something sounds too good to be true it usually is, and this study finds little evidence that alcohol is protective.”
