A team led by scientists at the University of Cambridge, UK, and Fudan University, China, examined the ‘proteomes’ — the suite of proteins — in blood samples donated by over 42,000 adults aged 40-69 years who are taking part in the UK Biobank. This allowed them to 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.
The team calculated social isolation and loneliness scores for individuals. Social isolation is an objective measure based on, for example, whether someone lives alone, how frequently they have contact with others socially, and whether they take part in social activities. Loneliness, on the other hand, is a subjective measure based on whether an individual feels lonely.
After adjusting for factors like age, sex, and socioeconomic background, the researchers identified 175 proteins associated with social isolation and 26 proteins associated with loneliness in the blood samples. Notably, approximately 85 percent of the proteins associated with loneliness overlapped with those associated with social isolation.
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Many of these proteins are involved in immune function and inflammation, and have been linked to various health conditions, including cardiovascular disease, type 2 diabetes, and stroke. Using a statistical technique known as Mendelian randomization, the researchers further identified five proteins whose abundance was causally linked to loneliness.
Dr Chun Shen from the Department of Clinical Neurosciences at the University of Cambridge and the Institute of Science and Technology for Brain-Inspired Intelligence, Fudan University, said: “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.”
One of the proteins significantly elevated in individuals experiencing loneliness was ADM, a protein known to play a role in stress response and the regulation of stress hormones like oxytocin. Higher ADM levels were also associated with smaller volumes of the left caudate, a brain region involved in emotional processing. Furthermore, individuals with higher ADM levels exhibited an increased risk of early death.
Professor Barbara Sahakian from the Department of Psychiatry at the University of Cambridge said: “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’. We need to find ways to tackle this growing problem and keep people connected to help them stay healthy.”
