Heavy drinking in middle-age may increase stroke risk more than traditional factors

In a study of 11,644 middle-aged Swedish twins who were followed for 43 years, researchers compared the effects of an average of more than two drinks daily ("heavy drinking") to less than half a drink daily ("light drinking").

The study showed that:

• Heavy drinkers had about a 34 percent higher risk of stroke compared to light drinkers.
• Mid-life heavy drinkers (in their 50s and 60s) were likely to have a stroke five years earlier in life irrespective of genetic and early-life factors.
• Heavy drinkers had increased stroke risk in their mid-life compared to well-known risk factors like high blood pressure and diabetes.
• At around age 75, blood pressure and diabetes appeared to take over as one of the main influences on having a stroke.

Past studies have shown that alcohol affects stroke risk, but this is the first study to pinpoint differences with age.

"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," said Pavla Kadlecová, M.Sc., a statistician at St. Anne's University Hospital's International Clinical Research Center in the Czech Republic.

Researchers analyzed results from the Swedish Twin Registry of same-sex twins who answered questionnaires in 1967-70. All twins were under age 60 at the start. By 2010, the registry yielded 43 years of follow-up, including hospital discharge and cause of death data.

Researchers then sorted the data based on stroke, high blood pressure, diabetes and other cardiovascular incidents.

Almost 30 percent of participants had a stroke. They were categorized as light, moderate, heavy or non-drinkers based on the questionnaires. Researchers compared the risk from alcohol and health risks like high blood pressure, diabetes and smoking.

Among identical twin pairs, siblings who had a stroke drank more than their siblings who hadn't had a stroke, suggesting that mid-life drinking raises stroke risks regardless of genetics and early lifestyle.

The study is consistent with the American Heart Association's recommended limit of two drinks a day for men and one for women. That's about 8 ounces of wine (two drinks) for a man and 4 ounces (one drink) for a woman.

Regular heavy drinking of any kind of alcohol can raise blood pressure and cause heart failure or irregular heartbeats over time with repeated drinking, in addition to stroke and other risks.

"For mid-aged adults, avoiding more than two drinks a day could be a way to prevent stroke in later productive age (about 60s)," Kadlecová said.