A UK-led study of more than 300,000 adults has found that social isolation and loneliness are each linked to an older biological age than would be expected from a person’s chronological age, and that the combination of the two factors yields the greatest acceleration. The research, published in Health Psychology, also ties these conditions to a higher risk of death over a follow-up period of around 14 years.
Biological age differs from chronological age because it reflects the physiological condition of cells, tissues and organ systems. When biological age runs ahead of one’s actual age, researchers describe this as biological age acceleration, a state associated with greater risk of chronic illness and earlier mortality.
Isolation and loneliness are two distinct forms of social disconnection. Social isolation is an objective measure—less contact with others, living alone, seeing family or friends infrequently, and avoiding groups—whereas loneliness is a subjective feeling of emotional distress about feeling detached, which can occur even in crowded rooms.
Because the two do not perfectly overlap, the authors emphasise that simply boosting social contact may not fully offset health risks tied to loneliness, just as loneliness cannot be fully countered by contact alone. Previous work, they note, has linked loneliness and isolation with markers of inflammation and immune activity, which in turn relate to higher rates of heart disease, stroke, diabetes and death.
The study’s co-first author Rui Mao, a resident physician and postdoctoral researcher in dermatology at Xiangya Hospital of Central South University, and corresponding author Xin Meng of the same university and the First Affiliated Hospital of the University of South China, led a multinational team that examined how isolation and loneliness, alone and in combination, relate to biological aging and to mortality. They also looked at whether genetic predisposition to biological aging modifies these relationships, and whether acceleration explains any link to death.
Using data from 309,746 UK Biobank participants with an average age of about 56 and a roughly even split of men and women, the researchers tracked health and survival from 2006–2010 until July 2023, a median follow-up of 14.4 years. All analyses were statistical, controlling for a wide range of demographic, socioeconomic and health variables.
Isolation and loneliness were measured at baseline through questionnaires. Social isolation was scored 0 to 3, with one point for living alone, seeing friends or family less than weekly, and not taking part in weekly group activities. Loneliness was scored 0 to 2, with one point for often feeling lonely and one for rarely confiding in someone close. At baseline, 40% of participants had a moderate isolation score and 14% had a high isolation score, while 4% were classified as lonely.
To estimate biological age, the researchers used PhenoAge, a clinical formula based on routine blood tests that reflect physiology and organ function. Biological age acceleration was calculated as the difference between PhenoAge and what would be expected for a person’s actual age. A polygenic risk score was also computed to reflect inherited risk for biological age acceleration.
In fully adjusted models, which accounted for age, sex, race, income, education, neighbourhood deprivation, body mass index, smoking, drinking, physical activity, grip strength, diet, sleep, sun exposure and medical history, each one-point rise in the isolation scale equated to a 0.17-year increase in biological age acceleration, while each one-point rise in loneliness added 0.15 years. Compared with the least isolated participants, the most isolated individuals showed 0.33 years more biological age acceleration (about four months), and those who were lonely showed 0.24 years more (about three months).
The researchers stressed that these are modest average differences in an aging indicator, not estimates of months of life lost for any given person. “Their potential relevance lies in what they may reveal about social conditions and health across a large population,” they said.
Even after full adjustment, the team notes that their estimates may understate the overall association because some factors—such as smoking, sleep and chronic disease—could lie on the causal pathway between social disconnection and aging. When demographic and socioeconomic factors were the only controls, the most isolated group appeared about seven months biologically older, and the lonely group about nine and a half months older.
Breaking down the effects of individual questions, living alone was associated with 0.27 years of acceleration, not having someone to confide in with 0.22 years, not taking part in weekly social activities with 0.17 years, often feeling lonely with 0.14 years, and infrequent visits from friends or family with 0.09 years. A clear additive pattern emerged when isolation and loneliness were considered together: those who were both highly isolated and lonely exhibited the greatest acceleration.
“One finding that stood out was the association between limited emotional support and biological age acceleration,” Mao and Meng observed. “Not having someone to confide in showed an association at least comparable in magnitude to reporting feelings of loneliness. This reinforces the importance of looking beyond the number of social contacts to whether people have relationships in which they feel supported.”
Genetic data added another layer. The Mendelian randomisation analysis found that a genetic liability toward loneliness was positively linked to biological age acceleration, while genetic tendencies toward regular attendance at a gym or sports club, and involvement in a religious group, were linked to lower acceleration. Attending a pub or social club, however, showed no significant association.
Mortality findings were stark. Each one-point increment in social isolation was associated with a 13.9% higher risk of death from any cause, and each one-point increment in loneliness with an 8.9% higher risk, with increased death rates from coronary artery disease and cancer observed as well.
An exploratory mediation analysis suggested that only about 5.2% of the isolation–death link and 7.2% of the loneliness–death link could be statistically attributed to biological age acceleration, under the model’s assumptions.
The results align with other recent work, including Mayo Clinic studies using cardiovascular-age measures and independent research linking psychological well-being and aging in older populations. The authors caution that correlation does not prove causation and that reverse causality—worse health limiting social contact—remains possible. They emphasise that the measurements were taken at a single time point and that more diverse populations are needed to confirm the findings.
The researchers suggest that different forms of group activity may influence aging through different mechanisms: sports clubs and gyms may promote physical exercise, while religious participation has been linked to lower depression and better self-rated health. Although genetic risk and social disconnection appeared to act independently, reducing loneliness and isolation could benefit people across all levels of inherited risk.
“Our findings suggest that social connection deserves attention when we think about healthy aging,” the authors said. “Having people around and feeling emotionally connected are different experiences, so opportunities for social contact and access to meaningful support both deserve consideration. These findings provide a reason to take social well-being seriously, although they do not establish that increasing social contact will reverse aging.”
The study’s limitations include the possibility of reverse causality, the use of a single time-point assessment, and the reliance on a UK Biobank sample that is predominantly of European ancestry and may not generalise to other cultural contexts. The authors also note that their genetic instrument analyses are not a substitute for intervention trials.
The researchers conclude that further work is needed to determine whether changes in social connection are followed by changes in biological aging, preferably through repeated measurements and more diverse populations, and that intervention studies are required to test whether reducing loneliness or improving social support can yield measurable biological benefits.
The study, “Social Isolation, Loneliness, and Biological Aging Acceleration,” was authored by Rui Mao, Jiao Yuan, Tongtong Zhang, Fan Wang, Yun Zhong, Haonan Yuan, Fan Yang, and Xin Meng.
