A large new study confirms that loneliness is a risk factor for dementia.
Scientists from Florida State University (FSU) in Tallahassee used data on 12,030 individuals from the Health and Retirement Study, a United States government-sponsored longitudinal survey of a nationally representative sample of people aged 50 and older.
They report their findings in a paper that now features in The Journals of Gerontology: Series B.
"We are not the first people," says first study author Dr. Angelina Sutin, who is an associate professor in FSU's College of Medicine, "to show that loneliness is associated with increased risk of dementia."
"But this is by far the largest sample yet, with a long follow-up," she adds. "And the population was more diverse."
The study data contained measures of loneliness and social isolation and a range of risk factors, including behavioral, clinical, and genetic.
Through telephone interviews, individuals had also completed assessments of cognitive ability, a low score on which indicates dementia. They did this at the start of the study and then every 2 years for up to 10 years, during which 1,104 people developed dementia.
Dementia risk increased by 40 percent
When they analyzed the data, the researchers saw that loneliness — as measured at the start of the study — was associated with a 40 percent higher risk of developing dementia over the 10-year followup.
In addition, they found that the link was independent of gender, education, race, and ethnicity. Another notable finding was that it was also independent of social isolation.
People who reported feeling lonely were also more likely to have other risk factors for dementia, such as depression, high blood pressure, and diabetes. They were also likelier to smoke and be less physically active.
Even after adjusting for these risk factors, however, loneliness remained a strong predictor of dementia.
The World Health Organization (WHO) have defined dementia as a "syndrome in which there is deterioration in memory, thinking, behavior, and the ability to perform everyday activities."
There are approximately 50 million people worldwide living with dementia, and doctors diagnose around 10 million new cases every year. It is a major cause of older people's disability and loss of independence.
Loneliness is not the same as social isolation
These results appear to tell us that it is how lonely we feel, rather than the amount of social contact we have with others, that contributes to cognitive decline.
Dr. Sutin explains that their interpretation of loneliness refers to the "subjective experience of social isolation," as distinct from "actual social isolation," which is an objective measure.
Loneliness is "a feeling that you do not fit in or do not belong with the people around you," notes Dr. Sutin, giving the example of a person "who lives alone, who doesn't have very much contact with people, but has enough — and that fills their internal need for socializing."
A person can have lots of social contact, be surrounded by people, and "be socially engaged" but still feel like they do not belong. In this case, they would score low on social isolation but high on loneliness.
A 'modifiable risk factor'
Dr. Sutin suggests that their finding is important because it highlights the need not only to assess risk factors objectively, but also to consider how individuals "subjectively interpret their own situation."
Speculating on how loneliness and dementia could be linked, Dr. Sutin says that one way may be through inflammation and another could be through behavior, such as drinking heavily or being physically inactive.
Another way could be that cognitive function is affected by not having enough social interaction that is meaningful and engages the mind.
Either way, loneliness is a sign that our needs are not being met, and that is something we can change, she concludes.
"Loneliness is a modifiable risk factor."
Dr. Angelina Sutin