Pensioners were warned today not to binge-drink after new research revealed they could be damaging their brains.

Binge-drinking - defined as downing four or more drinks in one go - blunts thinking ability and memory in later life, the findings showed.

A heavy drinking session twice a month more than doubled the risk of men and women aged 65 and older suffering high levels of mental decline and memory loss.

Binge-drinking once a month had a lesser effect, but still increased the risk by up to 62%.

Other research has suggested that small amounts of alcohol may actually benefit the brain.

But the new British study showed a clear association between boozing to excess and cognitive impairment.

Lead scientist Dr Iain Lang, from the University of Exeter's Peninsula College of Medicine and Dentistry, said: "We know that binge-drinking can be harmful. For example, it can increase the risk of harm to the cardiovascular system, including the chance of developing heart disease, and it is related to increased risk of both intentional and unintentional injuries.

"In our group of community-dwelling older adults, binge-drinking is associated with an increased risk of cognitive decline. Those who reported binge-drinking at least twice a month were more than twice as likely to have the greatest decline in both cognitive function and memory.

"These differences were present even when we took into account other factors known to be related to cognitive decline such as age and level of education."

Dr Lang's team analysed eight years-worth of data on more than 5,000 men and women aged 65 and over.

All were participants in the Health and Retirement Study, a US investigation of ageing that collected a wealth of information about health and lifestyle.

Telephone interviews were conducted to assess mental performance and memory.

Binge-drinking once a month or more was reported by 8.3% of the men and 1.5% of the women.

A total of 4.3% of men and 0.5% of women were in the habit of binge-drinking twice a month or more.

The results, presented at the Alzheimer's Association International Conference in Vancouver, Canada, showed that twice-monthly binge-drinkers were 147% more likely to experience the highest levels of mental decline.

They were also 149% more likely than non-binge-drinkers to suffer the greatest amount of poor memory.

For once-monthly binge-drinkers, the risk for mental decline was raised by 62% and for memory by 27%.

Dr Lang added: "This research has a number of implications. First, older people - and their physicians - should be aware that binge-drinking may increase their risk of experiencing cognitive decline and encouraged to change their drinking behaviours accordingly.

"Second, policymakers and public health specialists should know that binge-drinking is not just a problem among adolescents and younger adults; we have to start thinking about older people when we are planning interventions to reduce binge-drinking."

An American study presented at the same meeting showed how lifetime drinking habits influenced the mental ability of 1,300 women aged 65 and older.

The research, led by Dr Tina Hoang, from the University of California at San Francisco, found that higher alcohol consumption in earlier life, moderate drinking in later life, and switching from non-drinking to drinking in later life all increased the risk of mental decline.

Dr Anne Corbett, research manager at the Alzheimer's Society, said: "There has been a lot of research into the link between alcohol and dementia. What is becoming increasingly apparent is that while an occasional tipple could actually help to protect the brain, binge-drinking could be linked to an increased cognitive decline.

"These latest studies help reinforce the link between heavy drinking and dementia, but we need much more research to better understand exactly how drinking alcohol affects the brain. In the meantime, eating well and exercising regularly are key ways of reducing your risk of dementia."

Dr Marie Janson, director of development at the charity Alzheimer's Research UK, said: "In a country with major concerns over binge-drinking, these new findings should be taken seriously by people of all ages. Many people will drink to relax and it's important to keep an eye on the amount of alcohol we consume.

"The findings make clearer the relationship between alcohol use and cognitive decline, and we see stark warnings against heavy drinking for both cognitive and a great many other health reasons.

"We still lack truly long-term research findings from a diverse population in this area, but the best advice is to keep alcohol consumption light throughout life to reap some benefits and protect against the risks of over-indulging."