It applies to people who have lost consciousness due to boozing in the last year, regardless of how much they drink each week. Scientists who carried out the research say having a large amount of alcohol in a short time may increase levels of neurotoxins that cause brain damage. They also found that people who drank more than the recommended 14 units per week but spread it over several days were 20 percent more likely to develop dementia than those who drank moderate amounts.
High alcohol consumption also raises risk of other disorders such as diabetes, heart disease and stroke, which in turn increases dementia risk.
Lead author Professor Mika Kivimaki, of University College London, said: "Guidelines on dementia prevention emphasise the importance of keeping overall alcohol consumption at moderate levels.
"It is also important to consider drinking patterns because we found that binge-drinking may be a longterm dementia risk factor even if a person usually drinks moderately."
The research team asked more than 130,000 people aged 18-77 about their drinking habits.
Moderate drinking was defined as anything up to 14 units per week, equivalent to around six pints of beer or seven medium glasses of wine.
Drinking more was "heavy".
After 14 years, 1,081 participants had dementia. The youngest was diagnosed at 27 and the oldest at 94.
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For all age groups, drinking to the point of blacking out increased their risk of getting dementia. The greatest effect was seen among people aged 60 and older, whose risk was tripled.
Prof Kivimaki said: "It is known that ethanol crosses the blood-brain barrier to reach neurons directly and, in high concentrations... can initiate pathologic processes leading to brain damage. So, one potential explanation is the neurotoxicity of alcohol." The study has been published in the journal Jama Network Open.
Fiona Carragher, of the Alzheimer's Society charity, said: "We've known for some time that drinking too much alcohol is linked to poor brain health.
"Future research should consider not only the amount of alcohol we consume but also drinking patterns to best help people reduce their risk."
Dr Sara Imarisio, at Alzheimer's Research UK, said: "The best current evidence indicates that as well as drinking safely, staying physically and mentally active, eating a healthy balanced diet, not smoking and keeping weight, cholesterol and blood pressure in check are all good ways to support a healthy brain as we age."
Andrew Misell, of Alcohol Change UK, said: "If you're worried about your own drinking, or that of someone you know, speak to your doctor or local alcohol service."