Alcohol consumption in excess has well-documented negative effects on both short- and long-term health, one of which is brain damage that can lead to Alzheimer's disease or other forms of dementia.

Can alcohol consumption increase dementia risk?

Excessive alcohol consumption over a lengthy time period can lead to brain damage, and may increase your risk of developing dementia. However, drinking alcohol in moderation has not been conclusively linked to an increased dementia risk, nor has it been shown to offer significant protection against developing dementia.

As such, people who do not currently drink alcohol should not be encouraged to start as a way to reduce dementia risk.

Conversely, those who drink alcohol within the recommended guidelines are not advised to stop on the grounds of reducing the risk of dementia, although cutting back on alcohol consumption may bring other health benefits.

What does the evidence say about alcohol and dementia?

Two reviews of the available evidence conducted by Alzheimer's Disease International and the National Institute for Health and Care Excellence (NICE) scrutinised multiple research studies of alcohol consumption and the development of dementia.

Both reviews used a systematic approach, that is one in which researchers evaluate the conclusions made in multiple previously published research studies.

While this may sound like a re-run of old data, it is a powerful approach that allows us to make stronger conclusions on a given topic. If multiple studies using varied methods and studying different groups of people come up with the same conclusion, then we can be more certain of the conclusion for the whole population.

These reviews found that individuals who drank heavily or engaged in binge drinking - where a person consumes a large quantity of alcohol in a short time period - were more likely to develop Alzheimer's disease or any other form of dementia than those who engaged in moderate alcohol consumption (see below for definition).

The research evaluated by NICE focused on large populations of hundreds or even thousands of people, starting in mid-life (age 40-64) and tracked them for over five years, sometimes well in to old age, to trace how long term behavioural patterns could impact dementia risk.

How can alcohol damage the brain?

Heavy alcohol consumption over a long period of time can lead to brain damage. People who drink heavily over a long period of time are more likely to have a reduced volume of the brain's white matter, which helps to transmit signals between different brain regions. This can lead to issues with the way the brain functions.

Long-term heavy alcohol consumption can also result in a lack of vitamin thiamine B1 and Korsakoff's Syndrome, a memory disorder affecting short term memory.

What is moderate alcohol consumption?

These reviews typically defined moderate alcohol consumption as 1-14 units of alcohol per week for women and 1-21 units a week for men. NHS guidelines published in 2016 state that both men and women should limit their intake to 14 units a week. A unit is dependent on the amount of pure alcohol in a given volume and can be calculated for specific drinks here. According to the NHS, a basic guideline for units of alcohol is as follows:

• A typical glass (175mL) of (12%) wine: 2 units
• A pint of lower (3.6%) alcohol beer or cider: 2 units
• A pint of higher (5.2%) alcohol beer or cider: 3 units
• A single shot (25mL) of spirits such as whisky, gin or vodka (40%): 1 unit

Is moderate alcohol consumption safe for the brain?

Some research has indicated that individuals who drank in moderation were less likely to develop Alzheimer's disease or any other form of dementia than those who consumed zero alcohol.

Some protective effects of alcohol have been seen on the brain, such as reduced thickness of blood (called plasma viscosity) and increased levels of healthy cholesterol (also known as HDL cholesterol) in the body. Both of these effects have been suggested to help lower the risk of developing dementia.

However, the evidence produced by studies that link moderate alcohol consumption with a lower likelihood of Alzheimer's disease does have some flaws. For example, many of these studies classified 'non-drinkers' as both people who have given up alcohol consumption due to health reasons (such as previous alcoholics) and lifetime non-drinkers.

These two subsets of people are actually quite different as people who have given up drinking for health reasons may have already had alcohol-induced brain damage, so are more likely to be similar to people in the heavy-drinking category than lifetime non-drinkers.

Therefore the mixing of these distinct populations into one study group may have skewed the results and lead to conclusions which overstate the potential risk of not drinking alcohol to developing Alzheimer's and dementia.

It is important that future research differentiates between lifetime non-drinkers and individuals who have given up drinking for health reasons to clarify these findings. One such study has shown no evidence for a protective effect of moderate alcohol consumption on the development of dementia although we will need to see the results of further studies that make this distinction before we can fully understand this relationship.

What should I take away from this research?

The link between alcohol and dementia (or lack thereof) in non-drinkers however is not fully understood and individuals who do not currently drink alcohol should not start as a method of protection against the development of dementia.

From the evidence collected to date, it is not possible to determine what effect drinking within the NHS recommended alcohol guidelines has on a person's risk of dementia.