The Long-Lived Physical Effects of Loneliness

For millions of years, most mammals have known not to stay alone for too long. Cavemen went hunting in tribal groups, built interpersonal relationships, and lived in nomadic communities. Wolves would roam in packs, taking turns watching over shelter while the others rested. Even fish swam in schools to aid navigation and protect against predators.

In recent years, cases of social isolation have become increasingly common. With tools such as social media platforms and online meeting softwares, physical social gatherings do not prove as useful and necessary as they did in, say, the 2000s. In fact, the World Health Organisation reports that an estimated 1 in 4 older people are experiencing social isolation and between 5% and 15% of adolescents are experiencing loneliness.

In his 2020 commentary on social isolation and loneliness among older adults in the context of COVID-19, researcher Bei Wu defines social isolation as “the objective state of having few social relationships or infrequent social contact with others”, and loneliness as “a subjective feeling of being isolated”. Although the difference in objectivity between the two is made clear, one is oftentimes a subset of the other: isolation begets loneliness, and loneliness may cause a person to self-isolate. Regardless, one thing is clear for both –the state of isolation and the feeling of loneliness can bring about drastic change to one’s health.

It’s common knowledge that loneliness can affect our bodies, such as disrupting our sleep schedule or causing a change in our appetite. But recent research has revealed that prolonged periods of social isolation can have long-term effects on our physical health, implicating chronic conditions that stick with us for life. Cumulative evidence suggests that both social isolation and loneliness are linked to morbidity and mortality.

Researchers from various universities across the United Kingdom and from Shanghai, China, discovered that loneliness and social isolation were linked to the prevalence of proteins which were linked to cardiovascular disease, type 2 diabetes, stroke and mortality.

The researchers formed a group of over 42,000 middle-aged test participants, with half being male and half female, who had quality-controlled data relating to existing proteins and health conditions. Among these, 9.3% reported being socially isolated and 6.4% reported feeling lonely. Researchers identified certain proteins that were more prevalent in those who were reported to be self-isolated and/or feeling lonely. The test participants were then observed for almost 14 years.

Graph showing the association between proteins identified to be more prevalent in socially isolated and/or lonely people (GDF15, PLAUR, etc.) with the incidence of 5 diseases (cardiovascular disease, dementia, type 2 diabetes, depression, stroke) and mortality.

As shown in the above graph, the identified proteins were associated with the diseases mentioned above. This relationship is corroborated with the results of the long observation period: 2,695 participants developed CVD, 892 developed all-cause dementia, 1,703 developed T2D, 1,521 developed depression, 983 developed stroke and 4,255 passed away.

The researchers found none of the proteins appeared to cause social isolation or loneliness, implying that the test participants who were genetically predisposed to produce more of these proteins were not any more susceptible to feeling lonely than their peers. However, loneliness and social isolation caused the levels of these proteins to increase. The identified proteins, by nature, trigger the inflammatory system, causing changes in the body's response to external stimuli, which might have made the body more susceptible to the above-mentioned diseases.

Similar results signposting the link between loneliness and mortality were obtained from a 2019 study which found that over an observation period of 14 years, out of 1363 adult Swedes, death occurred with an incidence rate of 2.63 per 100 person-years for lonely individuals, and 2.09 per 100 person-years for non-lonely individuals.

Though the direct relationship between loneliness and the susceptibility to these diseases remains to be investigated, one thing is certain – humans require positive social interaction to survive and thrive. No man is an island, shown even in the way our bodies react to social isolation and loneliness.

Sources:

1. Shen, C., Zhang, R., Yu, J. et al. Plasma proteomic signatures of social isolation and loneliness associated with morbidity and mortality. Nat Hum Behav (2025). https://doi.org/10.1038/s41562-024-02078-1

2. Social isolation and loneliness. (2023, November 15). https://www.who.int/teams/social-determinants-of-health/demographic-change-and-healthy-ageing/social-isolation-and-loneliness

3. Henriksen, J., Larsen, E. R., Mattisson, C., & Andersson, N. W. (2019). Loneliness, health and mortality. Epidemiology and Psychiatric Sciences, 28(2), 234–239. doi:10.1017/S2045796017000580

Image Credit

1. https://www.psychologicalscience.org/news/releases/understanding-loneliness-through-science.html