In 2019 a startling article was published in the New England Journal of Medicine. Researchers tracked brain changes in nine polar scientists after 14 months isolated at a remote station in Antarctica. The data revealed striking structural brain changes, with a number of crucial regions actually shrinking during their time spent alone at the distant outpost.
The association between loneliness or social isolation and poor health has been known for some time. Plenty of large-scale epidemiological studies have linked increased risk of stroke, dementia, and cardiovascular problems to various degrees of social isolation. But what hasn’t been completely clear is exactly how these things are connected.
Some studies have hypothesized it's just the lack of social interaction that simply leads to bad habits and ultimately poor health. Maybe you eat more and exercise or move less by virtue of not seeing other people? It’s possible the link is correlation and not causation. Except research like the unexpected Antarctica brain study seemed to suggest something else is at play.
Now, a new study published in Nature Human Behavior is offering some of the clearest insights into the physiological effect of loneliness to date. The research looked at what are called “proteomic” signatures in around 42,000 people. These are essentially the different combinations of proteins found in people either socially isolated or lonely, compared to the data gathered from people who don’t identify with those characteristics.
"There are more than 100,000 proteins and many of their variants in the human body,” explains co-author Jianfeng Feng. “AI and high throughput proteomics can help us pinpoint some key proteins in prevention, diagnosis, treatment and prognosis in many human diseases and revolutionize the traditional view of human health.”
The research initially homed in on just under 200 proteins that were associated with social isolation and loneliness. Social isolation (measured through objective factors including volumes of social contact and living situations) was found to be significantly more impactful on protein associations compared to loneliness (a subjective characteristic measured by asking participants how they feel).
Using a modeling process called Mendelian Randomization the research identified five specific proteins that seemed to have a direct causal link with loneliness or social isolation. That is to say, the researchers believe heightened levels of these proteins are directly caused by loneliness.
“All proteins with a significant causal relationship with loneliness were correlated with the incidence of CVD [cardiovascular disease], T2D [type 2 diabetes], stroke and mortality,” the researchers write in the study.
Things got even more interesting when the researchers started looking at the relationship between brain region volumes and specific proteins. One protein, dubbed ADM, particularly stood out with high levels known to play a role in both the sympathetic nervous system (SNS) and hypothalamic–pituitary–adrenal (HPA) activity. These two systems influence systemic stress and inflammatory responses. High ADM levels were also linked to decreased volume in crucial brain regions regulating the body’s sense of wellbeing.
“The strongest association was found between ADM and the insula, a hub for interoceptive mechanisms,” the researchers explain in the study. “Interoception is proposed to function as a vital pathway for the brain–body interactions underlying the loneliness–health link. Other significant associations were observed between plasma ADM levels and the left caudate, a region involved in emotional, reward and social processes.”
The findings offer a fascinating insight into the fundamental importance of social connection to human health. And the direct relationship between brain size and loneliness adds compelling weight to certain theories of human evolution. For example, the social brain hypothesis, proposed by evolutionary anthropologist Robin Dunbar in the late 1990s, suggests large brains evolved in primates due to their increasingly complex social behaviors.
Co-author on the new study Barbara Sahakian, from the University of Cambridge, says the findings offer a compelling biological basis to the known links between social isolation and health problems. She suggests face-to-face interactions are a vital element to healthy human functioning.
“These findings drive home the importance of social contact in keeping us well,” says Sahakian. “More and more people of all ages are reporting feeling lonely. That’s why the World Health Organization has described social isolation and loneliness as a ‘global public health concern.' We need to find ways to tackle this growing problem and keep people connected to help them stay healthy.”
The new study was published in Nature Human Behavior.
Source: University of Cambridge
