Living alone could be a bigger risk factor for dementia than physical inactivity, diabetes and obesity, research suggests.

People over 55 who live by themselves are 30% more likely to develop dementia than those who live with others, according to a UCL-led study.

The researchers now believe social isolation plays a more important role in people getting dementia than previously thought.

Lead author Dr Roopal Desai, from UCL’s Division of Psychology & Language Sciences, said: “More and more people are living alone, particularly older people, and some studies have also suggested that increasing numbers of people are experiencing loneliness in countries such as the UK.

It might be because people who live alone experience more loneliness or more stress, both of which can have adverse physical health effects, or it may be due to a lack of cognitive stimulation which is needed to maintain neural connections

“Our findings suggest that low social contact could have serious implications for dementia rates, especially as dementia rates are already rising due to ageing populations.”

The researchers reviewed evidence from 12 studies in seven countries in Europe and Asia, concerning 21,666 people aged over 55.

They found a “significant link” between living alone and a person’s risk of developing dementia.

Using living alone as a proxy for social isolation, and assuming the relationship is causal, they estimate dementia cases in the over-65s could be reduced by 8.9% if social isolation was eliminated entirely.

This suggests living alone is a greater risk factor than physical inactivity, hypertension, diabetes or obesity.

Dr Desai said the study does not explain why this may be, but suggested “several plausible explanations”.

She continued: “It might be because people who live alone experience more loneliness or more stress, both of which can have adverse physical health effects, or it may be due to a lack of cognitive stimulation which is needed to maintain neural connections.”

Interventions such as social prescribing could help mitigate the detrimental effects of social isolation, the researchers say.

But they caution that loneliness may be a greater driver than living alone, as some people seek solitude by choice.

We’ve known for some time that lack of social contact can play a role in our risk of developing dementia later in life

Further research should examine whether the relationship between living alone and dementia can be accounted for by feelings of loneliness, the number of years spent living alone or recent bereavement.

Fiona Carragher, director of research and influencing at the Alzheimer’s Society, said: “We’ve known for some time that lack of social contact can play a role in our risk of developing dementia later in life.

“At a time where people have been socially isolated during the pandemic, this research, funded by Alzheimer’s Society, brings this potential risk into sharper focus.”

The review and meta-analysis is published in Ageing Research Reviews.