Socially isolated and lonely adults tend to have an older biological age than their chronological age would predict, and they face a higher risk of death, according to a study of more than 300,000 people in the United Kingdom published in Health Psychology. People who were both isolated and lonely showed the greatest gap between biological and chronological age.
Two people born on the same day can experience very different rates of physical decline. While chronological age simply tracks the number of years since birth, biological age measures the physiological condition of a person’s cells, tissues, and organ systems. When an individual’s biological age is higher than their chronological age, researchers refer to the gap as biological age acceleration, a state that predicts a higher risk of chronic illnesses and earlier death.
Social isolation and loneliness are two distinct forms of social disconnection that may influence this physiological wear and tear. Social isolation is an objective lack of contact with other people, characterized by living alone, seeing family or friends less than once a week, and staying away from community groups. Loneliness is the subjective emotional distress of feeling detached from others or lacking someone to confide in, which a person can experience even when surrounded by people.
Because the two do not always overlap, the authors note that simply increasing social contact may not fully offset the health risks tied to loneliness, and vice versa. Both forms of disconnection are thought to take a toll on the body through chronic psychological stress, poorer health habits, and immune system disruption. For example, a large longitudinal study drawing on the same UK Biobank cohort found that loneliness and social isolation were linked to elevated blood levels of specific inflammation and immune proteins, which in turn tracked with higher rates of heart disease, stroke, diabetes, and death over a 14-year follow-up.
The study was led by co-first author Rui Mao, a resident physician, assistant researcher, and postdoctoral researcher in the Department of Dermatology at Xiangya Hospital of Central South University. Corresponding author Xin Meng is a resident physician and assistant researcher in the Department of Dermatology at the First Affiliated Hospital of the University of South China and Xiangya Hospital of Central South University. Along with colleagues from several other Chinese medical institutions, they examined how social isolation and loneliness independently and jointly relate to biological age acceleration, whether genetic predisposition to biological aging modifies this relationship, and whether biological age acceleration helps link social disconnection to mortality.
“Our research focuses on aging and the factors that shape health across the lifespan,” Mao and Meng told PsyPost. “Social isolation and loneliness have been linked to poorer health, but their relationship with biological aging, particularly when they occur together, remains less clear. We wanted to understand whether having fewer social connections and feeling lonely were each associated with an older biological profile.”
To investigate these questions, the researchers analyzed data from 309,746 adults enrolled in the UK Biobank, a large national health database in the United Kingdom. The participants had an average age of about 56 at the start of the study, and 54 percent were female. They were recruited between 2006 and 2010 and had their health and survival tracked until July 2023, for a median follow-up period of 14.4 years. The study was a secondary analysis of existing cohort data, and no preregistration was reported.
At the initial assessment, participants completed questionnaires measuring their social habits and feelings. The researchers scored social isolation on a scale from 0 to 3, assigning one point each for living alone, visiting friends or family less than once a week, and not participating in weekly group activities such as sports clubs, religious groups, social clubs, or adult education classes. At baseline, 40 percent of participants had a moderate isolation score of 1, and 14 percent had a high isolation score of 2 or 3. Loneliness was scored from 0 to 2, with one point given for often feeling lonely and one point for almost never confiding in someone close; 4 percent of participants scored the maximum of 2 points and were classified as lonely.
To measure biological age, the scientists used an established clinical formula called PhenoAge, which estimates physiological age from routine blood biomarkers, including markers of inflammation and organ function. Biological age acceleration was calculated as how much older or younger a participant’s PhenoAge was than expected for their actual age. The team also calculated a polygenic risk score for each participant, which summarizes their inherited genetic predisposition toward biological age acceleration based on variations in their DNA.
In statistical models that controlled for age, sex, race, income, education, neighborhood deprivation, body mass index, smoking, alcohol use, physical activity, grip strength, diet, sleep patterns, sun exposure, and personal history of diabetes, cardiovascular disease, hypertension, stroke, and cancer, both forms of disconnection were tied to an older biological age. Each one-point increase on the social isolation scale corresponded to a 0.17-year increase in biological age acceleration, while each one-point increase on the loneliness scale corresponded to a 0.15-year increase. Compared to the least isolated participants, those in the most isolated group showed 0.33 years more biological age acceleration, or roughly four months. Participants classified as lonely had 0.24 years more biological age acceleration, or about three months, compared to those who were not lonely.
“These are modest average differences in an aging indicator, rather than estimates of months of life lost or predictions for an individual,” the researchers explained. “Their potential relevance lies in what they may reveal about social conditions and health across a large population.”
The authors note that their fully adjusted estimates likely understate the overall association, because some of the factors they controlled for, such as smoking, sleep, and chronic disease, may themselves be pathways linking social disconnection to aging. Accounting only for demographic and socioeconomic factors, the most isolated group was about seven months older biologically and the lonely group about nine and a half months older.
Looking at the individual survey questions in the fully adjusted model, living alone was associated with 0.27 years of biological age acceleration, lacking 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 having infrequent visits from friends or family with 0.09 years. When the researchers looked at social isolation and loneliness together, they found an additive pattern, meaning that people who were both highly isolated and lonely had the greatest biological age acceleration.
“One finding that stood out was the association between limited emotional support and biological age acceleration,” Mao and Meng noted. “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.”
When the researchers incorporated the genetic data, they did not detect a statistically significant interaction between genetic risk and social disconnection, meaning that isolation and loneliness did not multiply the effect of aging-related genes. However, the genetic and social risks stacked on top of one another. Compared to people with low genetic risk and minimal isolation or loneliness, participants who had both a high genetic risk for biological age acceleration and high social isolation were biologically older by roughly 1.7 years, while those with high genetic risk and loneliness were biologically older by about 1.85 years. For comparison, isolation and loneliness on their own were tied to gaps of about four and three months.
Subgroup analyses also indicated that the link between loneliness and biological age acceleration was stronger among men, people under age 60, those with lower incomes, people who never smoked, and those with unhealthy sleep habits. The association between social isolation and biological age acceleration did not vary significantly by sex, body mass index, or sun exposure.
To address the possibility that poor health causes people to withdraw socially rather than the other way around, the researchers also performed a two-sample Mendelian randomization analysis, which uses genetic variants associated with behavioral traits to test for a directional link to health outcomes. Because these genetic variants are fixed at conception, they are not affected by later health problems, which reduces the chance that poor health is driving the association. In this analysis, a genetic liability toward loneliness was positively associated with biological age acceleration, while genetic tendencies toward regular attendance at a gym or sports club and involvement in a religious group were associated with lower biological age acceleration. Genetic predisposition toward visiting a pub or social club did not have a statistically significant association with biological age acceleration.
Finally, the team examined death records over the 14.4-year follow-up period. Each one-point increase in the social isolation score was associated with a 13.9 percent higher risk of dying from any cause, and each one-point increase in the loneliness score was associated with an 8.9 percent higher risk of death from any cause. Both traits were also associated with higher rates of death specifically from coronary artery disease and cancer.
An exploratory mediation analysis examined whether biological age acceleration sat on the pathway between social disconnection and mortality. Under the model’s assumptions, only about 5.2 percent of the link between isolation and death, and 7.2 percent of the link between loneliness and death, was statistically attributable to biological age acceleration.
These findings align with a Mayo Clinic study that gauged biological age from artificial intelligence readings of heart electrocardiograms rather than blood tests, which likewise linked social isolation to accelerated biological aging and a higher risk of death. They also fit with a study of older Chinese adults that tied poorer psychological well-being, including loneliness and unhappiness, to older biological age, though that study measured loneliness as part of a broader well-being scale.
The authors suggest that different types of group activities may relate to biological aging through different channels. They propose that sports clubs and gyms may help because they incorporate regular physical exercise, whereas religious participation has been linked to lower rates of depression and better self-rated health. Because genetic risk and social disconnection operated independently rather than interacting, the researchers also note that reducing loneliness and isolation could benefit people across all levels of inherited genetic risk.
“Our findings suggest that social connection deserves attention when we think about healthy aging,” the researchers 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.”
As with all research, there are some caveats to consider when interpreting these results. Even with more than a decade of mortality follow-up, reverse causality cannot be ruled out, since people experiencing worse physical decline may become less able to socialize or more prone to feeling lonely.
“The main caution is that our findings should not be interpreted as proof that loneliness directly causes aging or that joining a social group will make someone biologically younger,” Mao and Meng told PsyPost. “Biological age was assessed at one time point, so we could not track how individuals’ aging trajectories changed as their social circumstances changed. Our genetic analyses provided complementary evidence, but they also depend on assumptions and cannot replace intervention trials.”
Those genetic instrument analyses carry several specific constraints. No genetic summary data were available for the complete social isolation score, so the Mendelian randomization could only test individual habits like gym or religious attendance rather than overall isolation. In addition, genetic variants linked to habits like gym attendance may influence biological aging through other biological pathways rather than through social participation itself, genetic proxies do not perfectly mirror actual survey responses, and the estimate linking genetic liability for loneliness to biological aging had a wide margin of error.
Finally, the questionnaires used in the UK Biobank relied on just a few brief items to capture loneliness and isolation and did not account for marital status in the index. The participant pool was also predominantly of European ancestry and drawn from the United Kingdom, meaning the results may not automatically generalize to other cultural environments where family structures and community norms differ.
Because the team studies aging from a dermatology perspective, their interests extend to how aging shows up in tissues like the skin. “Our broader goal is to identify potentially modifiable factors associated with biological aging and understand their relevance to health, including skin health,” the researchers explained. “An important next step would be to examine whether changes in social connection are followed by changes in biological aging, using repeated measurements and more diverse populations. Ultimately, intervention studies are needed to test whether reducing loneliness or improving social support can produce measurable biological benefits.”
“We hope this study encourages a more compassionate understanding of loneliness and social isolation,” Mao and Meng added. “Social circumstances are shaped by health, mobility, caregiving responsibilities, and access to community resources, so the implications extend beyond individual choices. Our findings support further investigation of social connection as part of the broader conditions that enable healthy aging.”
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.