Interactions with friends and family could help to keep us healthy by boosting our immune system and reducing our risk of diseases such as heart disease, stroke and type 2 diabetes, researchers suggest.
They studied proteins from blood samples taken from more than 42,000 adults aged 40 to 69, recruited to the UK Biobank.
It is known that social isolation and loneliness are linked to poorer health and an early death but the mechanisms through which social relationships impact our health have been poorly understood.
A team led by scientists at the University of Cambridge, and Fudan University, China, examined the ‘proteomes’ – collection of proteins – in the blood samples to see which proteins were present in higher levels among people who were socially isolated or lonely, and how these were connected to poorer health.
For each person, they calculated a social isolation score – an objective measure based on factors such as whether someone lives alone, the frequency of their contact with others socially and whether they take part in social activities.
And they calculated a loneliness score – a subjective measure based on whether an individual feels lonely.
Analysing the proteomes and adjusting for factors such as age, sex and socioeconomic background, the team found 175 proteins associated with social isolation and 26 proteins associated with loneliness. Approximately 85 per cent of the proteins associated with loneliness were also linked to social isolation.
Many of these proteins are produced in response to inflammation, viral infection and as part of immune responses, as well as being linked to cardiovascular disease, type 2 diabetes, stroke and early death.
A statistical technique called Mendelian randomisation was used to explore the causal relationship between social isolation and loneliness on the one hand, and proteins on the other, identifying five proteins whose abundance was caused by loneliness.
One linked to loneliness – ADM – is known to play a role in responding to stress and in regulating stress hormones and social hormones such as oxytocin – the so-called ‘love hormone’ – which can reduce stress and improve mood.
The researchers found a strong association between ADM and the volume of the insula, a brain hub for interoception, which is our ability to sense what’s happening inside our body. The higher the ADM levels, the smaller the volume of this region.
Higher ADM levels were also linked to lower volume of the left caudate – a region involved in emotional, reward and social processes. Higher levels of ADM were also linked to increased risk of early death.
Another protein, ASGR1, is associated with higher cholesterol and an increased risk of cardiovascular disease.
Other identified proteins play roles in the development of insulin resistance, atherosclerosis – the furring of the arteries – and cancer progression.
Dr Chun Shen, from the Department of Clinical Neurosciences at Cambridge and the Institute of Science and Technology for Brain-Inspired Intelligence at 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.”
Prof Jianfeng Feng, from the University of Warwick, said: “There are more than 100,000 proteins and many of their variants in the human body. AI and high throughput proteomics can help us pinpoint some key proteins in prevention, diagnosis, treatment and prognosis in many human diseases and revolutionise the traditional view of human health.
“The proteins we’ve identified give us clues to the biology underpinning poor health among people who are socially isolated or lonely, highlighting why social relationships play such an important part in keeping us healthy.”
Prof Barbara Sahakian, from the Department of Psychiatry at 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.”
The findings are published in the journal Nature Human Behaviour.
The research was supported by the National Natural Sciences Foundation of China, China Postdoctoral Science Foundation, Shanghai Rising-Star Program, National Key R&D Program of China, Shanghai Municipal Science and Technology Major Project, 111 Project, Shanghai Center for Brain Science and Brain-Inspired Technology, and Zhangjiang Lab.
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