It is well known that high blood pressure and diabetes can raise the risk of stroke. But a new twin study finds that, for middle-aged individuals, there may be one factor that increases this risk even more: heavy alcohol consumption.

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Heavy drinking in midlife was found to raise the risk of stroke by 34%, compared with light drinking.

Pavla Kadlecová, a statistician at the International Clinical Research Center of St. Anne’s University Hospital in the Czech Republic, and colleagues found that consuming more than two alcoholic drinks a day during middle age increases the risk of stroke by more than a third.

The team publishes their findings in Stroke – a journal of the American Heart Association (AHA).

Each year, more than 795,000 people in the US have a stroke. The condition is also responsible for almost 130,000 deaths each year, making it one of the leading causes of death in the country.

High blood pressure (hypertension), diabetes, smoking and high cholesterol are among the major, well-known risk factors for stroke. Past studies have indicated that heavy alcohol use is also an important risk factor for stroke, but Kadlecová and colleagues say their study is the first to look at how this risk varies by age.

To reach their findings, the team analyzed 11,644 same-sex twins from the Swedish Twin Registry. Between 1967 and 1970 – when the participants were under the age of 60 – they completed dietary questionnaires, from which researchers could gather information on their alcohol consumption.

The twins were followed for around 43 years, until 2010. The researchers analyzed their health data over this period, including hospital discharge information and details on causes of death, as well as information on blood pressure, smoking and diabetes, among other health risks.

During the follow-up period, nearly 30% of participants had a stroke. The researchers divided the participants into three groups dependent on their alcohol consumption at study baseline: “light” drinkers (half an alcoholic drink a day), “moderate” drinkers (up to two drinks a day) and “heavy” drinkers (more than two drinks a day).

The researchers note that these definitions for alcohol consumption are in line with recommendations from the AHA, which state that a man should drink no more than two alcohol beverages a day and a woman should consume no more than one.

The team found that participants classed as heavy drinkers were 34% more likely to have a stroke than those classed as light drinkers. In addition, participants who engaged in heavy drinking in their 50s and 60s were likely to suffer a stroke around 5 years earlier than those who were light drinkers.

Siblings who had a stroke were found to consume more alcohol than their identical twins who did not have a stroke, indicating that heavy alcohol consumption during middle age raises stroke risk independently of genetic and early-life factors.

On comparing the effects of alcohol consumption on stroke risk with the effects of traditional risk factors – such as high blood pressure and diabetes – the team found that alcohol consumption was a bigger influence during middle age. However, high blood pressure and diabetes appeared to be stronger risk factors for stroke from the age of 75 and over.

Commenting on their findings, Kadlecová says:

We now have a clearer picture about these risk factors, how they change with age and how the influence of drinking alcohol shifts as we get older. For mid-aged adults, avoiding more than two drinks a day could be a way to prevent stroke in later productive age (about 60s).”

While many studies have associated heavy alcohol consumption with negative health implications, a recent study reported by Medical News Today found that drinking up to seven drinks a week may reduce the risk of heart failure.