Alcohol and dementia - is moderate drinking safe?

There is no doubt that alcohol abuse is bad for the brain - but could there be health benefits for moderate drinkers?

Who are moderate drinkers?

They are people who drink alcohol every week, but not to excess.

Drinking "in moderation" is usually taken to mean consuming seven to 14 units of alcohol a week, equivalent to six pints of average-strength beer or seven glasses of wine.

The UK guidelines say that drinking no more than 14 units a week on a regular basis will keep health risks to a low level.

Light drinkers are those who drink fewer than that - between one and seven units.

So moderate drinking is OK?

The research is contradictory and so the answer isn't straightforward.

Some research suggests that drinking one or two units of alcohol a day - particularly red wine - could be of benefit to brain health, but other scientists are more sceptical.

A study published on Thursday in the British Medical Journal found that moderate drinkers were at lowest risk of dementia, compared to heavy drinkers and non-drinkers, but this may be because they tend to lead generally healthy lives and are less likely to smoke or eat unhealthily.

Another study found that, even in moderation, drinking alcohol could increase the risk of dementia.

Analysis by BBC Reality Check

Another study has come out to add to the confusing picture of public health advice around drinking.

The British Medical Journal study found that a group of people who did not drink alcohol in middle age were more likely to develop dementia later on than people who drank moderately.

So should non-drinkers take up the habit for the sake of their health? The answer is almost certainly no.

There are a few reasons this study should be treated with caution.

First of all, it can only really say that more of the people observed who didn't drink in midlife went on to develop dementia - it cannot say that abstaining from drinking itself is causing dementia.

And people in this group may have drunk heavily in the past or had to give up drinking for health reasons.

The study only looked at whether people drank during a particular snapshot in time, so some of that group might already be in poor health.

There have been a number of studies in this area with conflicting results and this one doesn't provide enough evidence to suggest that anyone should go ahead and change their drinking habits.

How can alcohol damage the brain?

Drinking alcohol can cause your blood pressure and blood cholesterol to rise which, in turn, can damage the blood vessels supplying the brain, causing problems like vascular dementia.

It can also damage memory.

Continuous heavy drinkers, including binge drinkers and those who are dependent on alcohol, are most at risk from harming their brains in this way and developing dementia.

Recent research from France found that people who were dependent on alcohol or had a health issue caused by regular heavy drinking were three times more likely to develop dementia than other people.

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

Another study of drinking habits in 19 countries found that regular excess drinking could shorten a person's life by between one and two years.

The same research warned that people who drank more than 18 alcoholic drinks a week could lose four to five years of their lives.

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Is there any safe level, in that case?

The chief medical officer in England says that drinking any level of alcohol carries a health risk for anyone.

The more you drink on a regular basis the greater the risk of developing a range of health problems.

These include liver disease, cancer, heart attacks and stroke.

Current UK guidelines advise that men and women should drink no more than 14 units of alcohol a week.

Experts say keeping to this limit and cutting out heavy drinking episodes during the week, while keeping several days alcohol-free each week, lowers the risk of health problems - as well as accidents and injuries.

How many units of alcohol are in each drink?

• 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

Source: NHS Choices