The cigarette cancels out the protective effect of alcohol
Sensible drinking can substantially reduce your risk of a stroke, but only if you don't enjoy a cigarette at the same time, research suggests.
A study of over 20,000 people in the UK found non-smokers who drank moderate amounts were nearly 40% less likely to have a stroke than non-drinkers.
But once cigarettes were added, this protective effect vanished.
The findings are being presented at a meeting of the American Academy of Neurology in Toronto.
The study, led by Cambridge University, looked at 22,254 people over 12 years. There were nearly 900 strokes.
People who stayed within moderate drinking guidelines - one or two small glasses of wine a day for a woman and slightly more for a man - saw a 37% decrease in their risk of stroke.
But this was only true if they did not smoke, with smoking drinkers and smoking non-drinkers seeing similar levels of risk.
"Our findings could have public health implications in that we appear to have a clearer understand of the dangers of combing smoking and moderate drinking on overall stroke risk," according to lead researcher Yangmei Li.
Large quantities of alcohol are known to increase the chance of a stroke by raising blood pressure, a key risk factor.
But alcohol does thin the blood, so can prevent clots forming. It may also affect the way cholesterol is carried in the bloodstream, reducing the risk of the build-up of fatty deposits in the blood vessel walls.
Smoking, however, causes the arteries to fur up, making the blood more likely to clot. This increases the risk of a stroke.
The study suggests that alcohol does not prevent this process that smoking kicks off.
"The links between smoking and stroke are clear - 10% of stroke deaths and a quarter of all strokes are linked to smoking. So giving up smoking is a vital step in reducing your risk of stroke," says Joe Korner of The Stroke Association.
"It is also important to note that drinking moderate amounts of alcohol does not protect against haemorrhagic strokes - those caused by a bleed, and in some cases it may in fact increase the risk. And we know that drinking more than the recommended alcohol limit increases your risk of all types of stroke."