Moderate drinking may actually improve brain power, according to Japanese research.

It is thought that an ingredient of alcoholic drinks may help prevent or restrict the hardening of the arteries which could lessen blood flow to the brain.

However, there are other factors linked to moderate alcohol consumption which could also be linked to improved IQ.

The researchers, at the National Institute for Longevity Sciences in Aichi Prefecture, near Tokyo, tested the IQs of 2000 people between 40 and 79 years old.

Men who drank less than 540 millilitres of sake or wine a day had an IQ 3.3 points higher than men who did not drink at all.

Women drinkers scored 2.5 points higher than teetotallers.

Senior researcher Hiroshi Shimokata told New Scientist magazine said: "It's very difficult to show a cause-effect relationship.

Raw fish

"We screened subjects for factors such as income and education, but there may be other factors such as lifestyle and nutritional intake."

In particular, he pointed out that those who drank sake tended to eat larger quantities of raw fish, which is thought to have possible benefits to cognitive function, while wine drinkers tended to eat more cheese, which may have a similar effect.

Dr Jonathan Chick, a senior lecturer in psychiatry at Edinburgh University, echoed this, saying that other studies had noted this association between moderate alcohol and brain function, but could not prove that the alcohol was definitely the reason.

"It's so difficult to take other factors into account - for example, moderate drinkers might have a better social environment," he told BBC News Online.

"I don't think I would want to tell somebody who isn't drinking to start, as they may be teetotal for very good reasons.

"However, for someone who has had a stroke due to blood clotting, I would not tell them to stop drinking moderately."

However, he spelled out the dangers of heavy drinking, particularly binge drinking, which is know to actually reduce brain power.