Study reveals direct link between loneliness, disease causing proteins

Among socially isolated and lonely people, researchers have found higher levels of proteins, including those produced in response to stress and those related with higher cholesterol, suggesting a possible "direct consequence of loneliness".

While social isolation and loneliness are known to be linked to poor health, the study, published in the journal Nature Human Behaviour, provides evidence of biological processes by which social relationships impact health. Loneliness is one's perception of how disconnected they feel from society.

Researchers at the University of Cambridge, UK, and Fudan University, China, therefore suggested that interactions with friends and family could keep us healthy by boosting our immune system and reducing risk of diseases such as heart disease, stroke and type 2 diabetes.

"These findings drive home the importance of social contact in keeping us well. 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'," lead author Barbara Sahakian, a professor at the department of psychiatry at the University of Cambridge.

"We need to find ways to tackle this growing problem and keep people connected to help them stay healthy," Sahakian said.

For the analysis, the researchers analysed proteins in blood samples of over 42,000 adults aged 40-69 years in the UK Biobank dataset. The team could thus see which proteins were present in higher levels among people who were socially isolated or lonely, and how these proteins were connected to poorer health.

Proteins are molecules produced by genes and are essential for helping bodies function properly.

The researchers found 175 proteins related to social isolation and 26 proteins linked to loneliness -- although there was substantial overlap, with most of the proteins linked to loneliness being shared with those of social isolation.

Many of these proteins are produced in response to inflammation, viral infection and as part of our immune responses, as well as having been linked to cardiovascular disease, type 2 diabetes, stroke, and early death, the researchers said.

The researchers then explored the causal relationship between social isolation and loneliness on the one hand, and proteins on the other, using Mendelian randomisation -- a genetic method of analysis to understand if a certain risk factor 'caused' a given outcome.

Five proteins were found to be abundant and caused by loneliness, including 'ADM' and 'ASGR1' -- while ADM has been studied to be produced in response to stress and for regulating stress-related hormones, ASGR1, is associated with higher cholesterol and an increased risk of cardiovascular disease.

Other proteins identified in the study are known to play roles in the development of insulin resistance and cancer growth.

"We know that social isolation and loneliness are linked to poorer health, but we've never understood why. Our work has highlighted a number of proteins that appear to play a key role in this relationship, with levels of some proteins in particular increasing as a direct consequence of loneliness," author Chun Shen, from the department of clinical neurosciences at the University of Cambridge, said.