Early Mortality Risk
Julianne Holt-Lunstad, PhD, professor of psychology and neuroscience at Brigham Young University in Provo, Utah, is the author of two large meta-analyses that suggest loneliness, social isolation, or living alone are independent risk factors for early mortality, increasing this risk by about a third — the equivalent to the risk of smoking 15 cigarettes per day.
“We have quite robust evidence across a number of health outcomes implicating the harmful effects of loneliness and social isolation. While these are observational studies and show mainly associations, we do have evidence from longitudinal studies that show lacking social connection, whether that be loneliness or social isolation, predicts subsequent worse outcomes, and most of these studies have adjusted for alternative kinds of explanations, like age, initial health status, lifestyle factors,” Holt-Lunstad said.
There is some evidence to suggest that isolation is more predictive of physical health outcomes, whereas loneliness is more predictive of mental health outcomes. That said, both isolation and loneliness have significant effects on mental and physical health outcomes, she noted.
There is also the question of whether loneliness is causing poor health or whether people who are in poor health feel lonely because poor health can lead to social isolation.
Finley said there’s probably a bit of both going on, but longitudinal studies, where loneliness is measured at a fixed timepoint then health outcomes are reported a few years later, suggest that loneliness is contributing to these adverse outcomes.
She added that there is also some evidence in animal models to suggest that loneliness is a causal risk factor for adverse health outcomes. “But you can’t ask a mouse or rat how lonely they’re feeling. All you can do is house them individually — removing them from social connection. This isn’t necessarily the same thing as loneliness in humans.”
Finley is studying mechanisms in the brain that may be involved in mediating the adverse health consequences of loneliness.
“What I’ve been seeing in the data so far is that it tends to be the self-report of how lonely folks are feeling that has the associations with differences in the brain, as opposed to the number of social connections people have. It does seem to be the more subjective, emotional perception of loneliness that is important.”
In a review of potential mechanisms involved, she concluded that it is dysregulated emotions and altered perceptions of social interactions that has profound impacts on the brain, suggesting that people who are lonely may have a tendency to interpret social cues in a negative way, preventing them from forming productive positive relationships.
Lack of Trust
One researcher who has studied this phenomenon is Dirk Scheele, PhD, professor of social neuroscience at Ruhr University Bochum in Germany.
“We were interested to find out why people remained lonely,” he said in an interview. “Loneliness is an unpleasant experience, and there are so many opportunities for social contacts nowadays, it’s not really clear at first sight why people are chronically lonely.”
To examine this question, Scheele and his team conducted a study in which functional MRI was used to examine the brain in otherwise healthy individuals with high or low loneliness scores while they played a trust game.
They also simulated a positive social interaction between participants and researchers, in which they talked about plans for a fictitious lottery win, and about their hobbies and interests, during which mood was measured with questionnaires, and saliva samples were collected to measure hormone levels.
Results showed that the high-lonely individuals had reduced activation in the insula cortex during the trust decisions. “This area of the brain is involved in the processing of bodily signals, such as ‘gut feelings.’ So reduced activity here could be interpreted as fewer gut feelings on who can be trusted,” Scheele explained.
The high-lonely individuals also had reduced responsiveness to the positive social interaction with a lower release of oxytocin and a smaller elevation in mood compared with the control individuals.
Scheele pointed out that there is some evidence that oxytocin might increase trust, and there is reduced release of endogenous oxytocin in high loneliness.
“Our results are consistent with the idea that loneliness is associated with negative biases about other people. So if we expect negative things from other people — for instance, that they cannot be trusted — then that would hamper further social interactions and could lead to loneliness,” he added.