LONDON - Blood pressure and stroke risk rise steadily the more alcohol people drink, and previous claims that one or two drinks a day might protect against stroke are not true, according to the results of a major genetic study.
The research, which used data from a 160,000-strong cohort of Chinese adults, many of whom are unable to drink alcohol due to genetic intolerance, found that people who drink moderately - consuming 10 to 20 grams of alcohol a day - raise their risk of stroke by 10 to 15 per cent.
For heavy drinkers, consuming four or more drinks a day, blood pressure rises significantly and the risk of stroke increases by around 35 per cent, the study found.
"The key message here is that, at least for stroke, there is no protective effect of moderate drinking," said Zhengming Chen, a professor at Oxford University's Nuffield Department of Population Health who co-led the research. "The genetic evidence shows the protective effect is not real."
The World Health Organisation (WHO) estimates that around 2.3 billion people worldwide drink alcohol, with average per person daily consumption at 33 grams of pure alcohol a day. That is roughly equivalent to two 150 ml glasses of wine, a large (750 ml) bottle of beer or two 40 ml shots of spirits.
This latest study, published in The Lancet medical journal, focused on people of East Asian descent, many of whom have genetic variants that limit alcohol tolerance.
Because the variants have specific and large effects on alcohol, but do not effect other lifestyle factors such as diet, smoking, economic status or education, they can be used by scientists to nail down causal effects of alcohol intake.
"Using genetics is a novel way ... to sort out whether moderate drinking really is protective, or whether it's slightly harmful," said Iona Millwood, an epidemiologist at Oxford who co-led the study. "Our genetic analyses have helped us understand the cause-and-effect relationships."
The research team - including scientists from Oxford and Peking universities and the Chinese Academy of Medical Sciences, said it would be impossible to do a study of this kind in Western populations, since almost no-one there has the relevant alcohol-intolerance gene variants.
But the findings about the biological effects of alcohol should be the same for all people worldwide, they said.
Europe has the highest per person alcohol consumption in the world, even though it has dropped by around 10 per cent since 2010, the WHO says, and current trends point to a global rise in per capita consumption in the next 10 years.