Passing out drunk could more than double the risk of later developing dementia, a study has found, with just one drink a day raising the risk by 22 per cent.
Researchers looked at dementia diagnoses in more than 130,000 adults in Europe who had reported their drinking habits some 14 years prior.
Those who said they had lost consciousness after drinking had a two-fold increased risk of dementia.
This was even if they regarded themselves as generally moderate drinkers with the occasional binge session. Alcohol was toxic to nerve cells in the brain and caused serious damage to them when people went overboard on their drinking, the study said.
The risk of dementia was even apparent for those who drank as little as two or three units or more of alcohol per day – the equivalent of a pint of beer or a large glass of wine.
These ‘heavy’ drinkers, breaching recommended limits set by health chiefs, had up to a 1.2-fold greater risk of developing the memory-robbing disease.
The findings suggest getting black-out drunk has a long-term affect on the brain, the researchers said, causing cognitive decline in later years.
People who said they had lost consciousness after drinking – regardless of how much alcohol they consumed – had a 2-fold increased risk of dementia (stock image)
The study, published today in the medical journal JAMA Network Open, was led by Dr Mika Kivimäki at University College London (UCL).
Researchers examined the results of seven separate studies that all investigated whether drinking was a dementia risk factor.
The studies spanned the UK, France, Sweden and Finland with 131,415 participants of an average age of 43.
Each study volunteer answered a questionnaire about their drinking habits before being categorised into heavy or moderate drinkers.
Some 103,290 were heavy drinkers because they consumed more than the limit recommended by UK and US health chiefs.
In the UK it is 14 units per week and in the US it is 21. Two units is the equivalent of a pint of lower-strength beer or a small to standard glass of wine.
The rest of the group, 28,125 people, were deemed moderate drinkers because they reported less than the advised limit.
The findings show those who drank more than 14 units per week had a 16 per cent higher chance of dementia, while those who breached 21 units had a 22 per cent higher odds.
Around 96,000 study participants were asked whether they had ‘passed out’ due to drinking during the past 12 months, either never, once, or several times.
Some 10.4 per cent of the study participants reported having lost consciousness after a drinking session in the past year.
The researchers say this may be an overestimate, considering many people refer to ‘passing out’ as simply going to sleep after drinking.
Those who passed out were more likely to throw back beers and spirits than wine.
Participants were divided into four groups: moderate drinkers who did or did not pass out, and heavy drinkers who did or did not pass out.
Moderate drinkers who pass out tend to be those who drink little but sometimes have episodes of excessive drinking, the researchers said.
Then the researchers used a range of electronic hospital and doctor records to work out who had been diagnosed with dementia in the 14 years following.
Losing consciousness once raised the odds of a dementia diagnosis by 2.1-fold, the study found, compared to those who drank moderately and never blacked out.
This rose to 2.2-fold in those who had a habit of passing out, reporting it more than once in the past year.
The risk was even across people who considered themselves both moderate and heavy drinkers.
The researchers explained that people who think of themselves as moderate drinkers may still be putting themselves at risk when they binge drink to the point of blacking out.
Dr Kivimäki told MailOnline: ‘A person’s average consumption can be moderate even if he/she has sometimes episodes of heavy binge drinking.
‘Our findings suggest that those who drink to the point of passing out are at increased risk of dementia even if their average consumption is moderate.’
He added that had the measure of ‘passing out’ been more precise – such as the level of alcohol in the blood – those who just fall asleep would not have been included.
‘The excess dementia risk might have been even higher as the exposed group would not include milder cases who only fell asleep,’ Dr Kivimäki said.
‘Unfortunately, objective measurement for alcohol-induced loss of consciousness are not easily scalable for a large real-life study, such as ours.’
Further analysis showed men were almost three times more likely to get dementia if they often blacked out, whereas women had twice the risk.
The paper said: ‘This increased risk suggests that the drinking pattern is important versus just the overall weekly quantity consumed.’
The researchers also looked at several other alcohol related health conditions, such as liver disease and kidney failure, and found they were higher among those who passed out from drinking.
These ‘contributed little’ to the main link between losing consciousness and dementia, the findings reveal.
Moreover, those who live a healthy lifestyle – other than for their habit of passing out – were not protected from the risks.
Dr Kivimäki and colleagues bluntly explain that alcohol is like poison to the brain, causing it to shrink and damaging important cells.
When it crosses the blood-brain barrier it infiltrates neurons in high concentrations.
Neurons send chemical messages around they brain. If they die, it leads to the classic symptoms of confusion, trouble understanding things and memory loss.
Atrophy describes a loss of neurons and the connections between them, and the authors wrote: ‘Alcohol can induce brain atrophy.’
When alcohol goes through the process of breaking down while in the brain, it can cause damage to cells, the paper warned.
Another possible explanation is that drinks that leads to loss of consciousness can mean someone falls and has repeated, mild head injuries. But the researchers could not support this theory given it would be difficult to measure.