Being lonely increases the risk of dementia by 40 percent, according to the biggest study of its kind.
Even those who feel like they don’t fit in the face and are surrounded by loved ones face a higher risk of neurological disorder, according to a 10-year study.
Scientists are currently unclear on exactly why being lonely could lead to dementia – the umbrella term for memory-robbing disorders.
However, they believe social isolation may trigger inflammation in the brain or could make a person more likely to lead an unhealthy lifestyle.
The cause of dementia remains unknown but the evidence is quickly mounting that a healthy diet and exercise can slash the risk.
Socialising may also be important to keep the mind engaged in a way that promotes cognitive health, the Florida State University team said.
The researchers, who analysed 12,030 people over the age of 50, now stress that loneliness is a ‘modifiable risk factor’.
The study involved the participants reporting on how lonely and socially isolated they felt, rather than how much social contact they actually had.
‘It’s a feeling that you do not fit in or do not belong with the people around you,’ lead author Dr Angelina Sutin said.
‘You can have somebody who lives alone, who doesn’t have very much contact with people, but has enough – and that fills their internal need for socialising.
‘So even though objectively you might think that person is socially isolated, they don’t feel lonely.
‘The flip side is that you can be around a lot of people and be socially engaged and interactive and still feel like you don’t belong.
‘From the outside it looks like you have great social engagement, but the subjective feeling is that you’re not part of the group.’
The participant’s cognitive status was assessed at the start of the study and every two years over the decade via telephone interviews.
During the study, published in the Journal of Gerontology: Psychological Sciences, 1,104 of the participants developed dementia.
Results suggested loneliness increases a person’s risk of dementia by 40 per cent, regardless of their sex, race, ethnicity or level of education.
And even after adjusting for factors such as lonely people being less active or more likely to smoke, their heightened risk of dementia remained.
‘We are not the first people to show that loneliness is associated with increased risk of dementia,’ Dr Sutin said.
‘But this is by far the largest sample yet, with a long follow-up. And the population was more diverse.’
Dr Sutin encourages those who feel socially isolated not to blame themselves. She said: ‘People might say, “You’re lonely. Go make a friend.” But it’s not that easy.’
The scientists believe their study highlights the importance of asking people if they feel lonely even if they appear to be socialising regularly.
‘Most people might describe periods where they felt lonely and then periods where they didn’t feel lonely,’ Dr Sutin said.
‘So just because you feel lonely now, you don’t always have to feel this way.’
In the US, one in ten people over 65 have dementia, while the condition affects 850,000 in the UK.