Social isolation and dementia risk explained

Studies have found differences in the brains of people who are socially isolated compared to people who are not. This suggests social isolation may affect how the brain works.

In one large study this was linked to a higher risk of developing dementia.

However no single factor causes dementia on its own. Social isolation is likely to be one part of a bigger picture of dementia risk, that includes our health, lifestyle and environment.

Staying socially connected is important for overall wellbeing. It may also help support brain health.

The exact link between social isolation, loneliness and dementia is not fully understood. More research is needed to unpick the relationship. But there are some possible explanations:

Fewer day-to-day interactions

Spending time with other people involves talking, listening and responding. People who are isolated may have fewer of these interactions. This may mean fewer chances to use memory and thinking skills in everyday life. Over time, this may affect how the brain works and makes it more susceptible to damage from diseases like Alzheimer’s.

Unhealthy lifestyle

People who are socially isolated may be more likely to have habits that affect their health. For example, they may be more likely to:

• be less physically active.
• smoke.
• drink more alcohol.
• have health conditions like high blood pressure.

All of these have been linked to a higher dementia risk.

Increased risk of depression

Social isolation can increase the risk of depression. Depression that lasts a long time, especially in midlife, has been linked to an increased risk of dementia later on.

For every 100 cases of dementia worldwide, almost half (45%) could be prevented or delayed. Five of those 45 cases are linked to social isolation in later life. 

So, if nobody experienced social isolation, there'd be five fewer cases of dementia for every 100 people who develop it now.

Find out more: Addressing 14 health and lifestyle factors could prevent nearly half of global dementia cases - Alzheimer's Research UK

Changes in the brain linked to dementia can begin many years before symptoms are noticed.

Some scientists suggest that social isolation may sometimes be an early sign of these changes, rather than something that increases the risk.

If this is the case, social isolation could be an effect of very early dementia, rather than a cause.

It’s also possible that both things are true – social isolation increases the risk of dementia, and those who are in the early stages of dementia become more socially isolated.

More research is needed to fully understand this two way relationship.

Most of what we know about dementia risk comes from observational studies, which follow groups of people over time to look for patterns in health and lifestyle.

For example, studies like Insight 46 have followed people for decades to understand how health across life is linked to brain health and later on.

This is often the most practical way to study dementia risk. Many risk factors cannot be tested in trials in a fair or ethical way. Dementia also develops over many years, so studies can take a long time to show results.

Observational studies can show when something like our diet or occupation are linked to a higher or lower chance of dementia. But they cannot prove that something directly causes dementia, or that changing it will definitely reduce risk. These studies look at patterns across large groups, not what will happen to any one person.

Randomised controlled trials give stronger evidence because participants are assigned to different groups at random. This design makes it more likely that differences in outcomes, for example our risk of dementia, are caused by the intervention, for example a diet change, rather than by other factors.

But these studies are harder to do in dementia research. They often take many years and may test several changes at once, making results harder to interpret.

Newer trials are helping to build a clearer picture of what may support brain health. No single study can give a definite answer, but it is all research findings together that help us understand what is important for our brain health and risk of dementia.