Feeling lonely, as distinct from being/living alone, is linked to an increased risk of developing dementia in later life,...
... those who lived alone or who were no longer married were between 70% and 80% more likely to develop dementia than those who lived with others or who were married.
And those who said they felt lonely were more than 2.5 times as likely to develop the disease. And this applied equally to both sexes.
When other influential factors were taken into account, those who said they were lonely were still 64% more likely to develop the disease, while other aspects of social isolation had no impact.
"These results suggest that feelings of loneliness independently contribute to the risk of dementia in later life,"...
They suggest that loneliness may affect cognition and memory as a result of loss of regular use, or that loneliness could itself be a sign of emerging dementia, and either be a behavioural reaction to impaired cognition or a marker of undetected cellular changes in the brain.