Over the course of the study, 9.3 percent of those living alone developed dementia and 5.6 percent of those living with another person had developed dementia. When controlling for other variables, researchers concluded that social isolation was not a strong predicator of dementia, but feelings of loneliness was a significant predicator. Those who had reported feeling lonely were 250 percent more likely to have developed dementia than their not lonely peers. When researchers adjusted for other factors, lonely individuals were still 64 percent more likely to develop dementia.

“These results suggest that feelings of loneliness independently contribute to the risk of dementia in later life,” the researchers say in the study. “Interestingly, the fact that ‘feeling lonely’ rather than ‘being alone’ was associated with dementia onset suggests that it is not the objective situation, but, rather, the perceived absence of social attachments that increases the risk of cognitive decline.”