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There are lots of reasons why drinking too much alcohol on a regular basis is not a good idea.

It can damage the liver, the heart and the brain and is bad for our general health - that much is known.

That is why UK guidelines advise men and women to drink no more than 14 units of alcohol a week, equivalent to six pints of average-strength beer or seven glasses of wine.

So what's the link with dementia?

Research shows that heavy drinking can increase the risk of developing dementia.

Alcohol abuse is toxic to the brain and can damage memory. It has also been shown to accelerate vascular brain damage. In other words, it's bad for your brain.

The Lancet Public Health has published new research from France on more than one million adults with dementia. Researchers found that being hospitalised with alcohol dependence or a health issue caused by continuous heavy drinking was a strong risk factor for the progressive brain condition, especially in the under-65s.

Their risk of dementia was three times greater than other people's.

But it's difficult to know whether it was a direct cause or just one factor among many.

Heavy drinkers are more likely to be smokers, have depression and lead unhealthy lives, which increases the risk of dementia.

How much did they drink?

No-one knows exactly. All we know is that they had alcohol use disorders which meant that their excessive drinking had become harmful and caused a serious health problem.

But we do know that drinking to this extent is likely to increase the risk of high blood pressure, diabetes, stroke and heart failure, which can also increase the risk of dementia.

Should moderate drinkers worry?

Most research suggests that drinking one or two units of alcohol a day - a small glass of red wine, particularly - could be of benefit to brain health.

But the advice is not straightforward because studies have also found that even in moderation, drinking alcohol could increase the risk of dementia.

However, there is a big difference between low-to-moderate drinking and people who drink in a way that is harmful - those who are binge-drinkers or alcohol-dependent.

What is the current advice?

According to the UK chief medical officers, we should stick to drinking no more than 14 units of alcohol a week. This keeps health risks to a low and safe level.

Large glass of wine - 3 units

Pint of higher-strength lager or beer - 3 units

Standard glass of wine - 2 units

Pint of lower-strength lager or beer - 2 units

Bottle of lager or beer - 1.7 units

Single shot of spirits - 1 unit

What do experts say?

Recognising that heavy drinking and being dependent on alcohol are going to increase the risk of developing dementia is important, they say.

Prof Tara Spires-Jones, from the Centre for Discovery Brain Sciences at the University of Edinburgh, said: "It is crystal clear that alcohol abuse is bad for your brain."

But there is also agreement that more research is needed to work out the role played by the volume of alcohol consumed against how often alcohol is drunk - and how this affects the risk of early-onset dementia.

Most cases of Alzheimer's disease, the most important cause of dementia, happen after the age of 65 and rise dramatically as people age. Discovering how to prevent those would be particularly useful.

Dr Doug Brown from the Alzheimer's Society said that "alcohol abuse disorders may be responsible for more cases of early-onset dementia than previously thought".

But he said the Lancet research did not change the current advice and did not suggest that moderate alcohol intake could cause early-onset dementia.

And there is a warning from Dr Sara Imarisio, head of research at Alzheimer's Research UK.

"People shouldn't be under the impression that only drinking to the point of hospitalisation carries a risk."

She said there were steps everyone could take to improve brain health.

"Although there is no surefire way to completely prevent dementia, the best current evidence indicates that as well as only drinking in moderation, 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."