Blood pressure and stroke risk increase steadily with increasing alcohol intake and previous claims that moderate drinking could be beneficial to health are dismissed by evidence from genetic research involving 160,000 adults.
Studies of genes that strongly affect how much alcohol people choose to drink show that alcohol itself directly increases blood pressure and the chances of having a stroke, according to a new study published in The Lancet. It was known that stroke rates were increased by heavy drinking, but it wasn’t known whether they were increased or decreased by moderate drinking.
Although people who have one or two alcoholic drinks a day had previously been observed to have a slightly lower risk of stroke and heart attack than non-drinkers, it was not known whether this was because moderate drinking was slightly protective, or whether it was because non-drinkers had other underlying health problems (eg, being former drinkers who had stopped because of illness). At least for stroke, the genetic evidence now refutes the claim that moderate drinking is protective.
READ MORE: Exceeding recommended drink limits takes years off lifeDr Peter Rice from Scottish Health Action on Alcohol Problems (SHAAP) said the study "further clarifies" the message that alcohol at any level of consumption does not improve your health and many important health risks increase the more you drink.
He shed light on previous studies which report that non-drinkers have higher rates of vascular disease, such as stroke and angina, than light drinkers but said these are being re-examined because some people who report that they are non drinkers have been problem drinkers in the past, who have stopped drinking. There is also a general trend that people who have had a stroke reduce or stop drinking altogether. So, according to Dr Rice the classification of these people as non-drinkers is misleading.
Dr Rice said: "The study of the effect of alcohol consumption on the risk of various diseases relies on accurate estimation of lifetime alcohol consumption. In general the risk of heart disease, stroke, several cancers and liver disease increases the more people drink. These health risks are in addition to the other harm related to alcohol such as crime, impact on family life and employability."
He added: "This study gets around the problem of accurate recording of consumption by using genetic methodology to estimate people’s likelihood, throughout their lifetime, of a particular drinking pattern. This study was undertaken in Asia looking at stroke and the results are consistent with a similar study four years ago in people of European ancestry looking at heart disease. These show that the less you drink, the lower your risk of vascular disease such as stroke or coronary heart disease. The increasing number of people in Scotland who don’t drink at all, now about 1 in 5 of the population, are likely to experience benefits to their health from not drinking."
As the genetic factors that strongly affect drinking patterns are allocated randomly at conception and persist lifelong, this study is the genetic equivalent of a large randomised trial, and can therefore sort out cause-and-effect relationships reliably - a method called “Mendelian randomisation.”
Alison Douglas, chief executive of Alcohol Focus Scotland said, “This study is a welcome addition to the mounting evidence that drinking any amount of alcohol increases the risk of damage to health, and that the risk generally increases in line with how much you drink. It is important the public are made aware of the risks, and understand that to keep the chances of stroke, cancer, accidents and mental health problems low, it’s best to stick within the Chief Medical Officers guidelines of up to 14 units a week for both men and women.
"Alcohol Focus Scotland believes the introduction of mandatory labelling of alcohol drinks, including number of units and health warnings, would help each of us to understand and manage our risk of alcohol health problems.”
Lead author Dr Iona Millwood, from the Medical Research Council Population Health Research Unit at the University of Oxford, UK, says: “Using genetics is a novel way to assess the health effects of alcohol, and to sort out whether moderate drinking really is protective, or whether it’s slightly harmful. Our genetic analyses have helped us understand the cause-and-effect relationships.”
Researchers from Oxford University, Peking University, and the Chinese Academy of Medical Sciences led a large collaborative study of over 500,000 men and women in China who were asked about their alcohol intake and followed for ten years.
Among men, these genetic variants caused a 50-fold difference in average alcohol intake, from near zero to about four units (drinks) per day. The genetic variants that decreased alcohol intake also decreased blood pressure and stroke risk. From this evidence, the authors conclude that alcohol increases the risk of having a stroke by about one-third (35%) for every four additional drinks per day (280 g of alcohol a week), with no protective effects of light or moderate drinking.
Professor Zhengming Chen, co-author from the Nuffield Department of Population Health, University of Oxford, says: “There are no protective effects of moderate alcohol intake against stroke. Even moderate alcohol consumption increases the chances of having a stroke. The findings for heart attack were less clear-cut, so we plan to collect more evidence.”