Abstract
Social frailty is common and associated with several adverse outcomes in older adults. However, its prevalence and effects on mortality in younger populations and the underlying cause of mortality are poorly understood. To examine the association of social frailty with all-cause and cause-specific mortality in adults across a wide age spectrum, we used data from the UK Biobank, a prospective cohort included 421,644 individuals aged 37–73 years enrolled from 2006 to 2010. Social frailty status was assessed based on Bunt’s concept (financial difficulty, live alone, less social activity and rarely contacts with friends/family). The prevalence of pre-social frailty and social frailty were 35.74% and 19.87%, respectively, indicating that more than half of the participants were at risk of cumulative depletion of essential social resources. Both pre-social frailty and social frailty were associated with higher risk of all-cause and cause-specific mortality (including malignant neoplasms, heart disease, cerebrovascular diseases, respiratory diseases, diabetes mellitus, and others caused) in adults across a wide age spectrum, independent of sociodemographic factors, lifestyles, chronic diseases, mental health, and physical frailty status. These findings indicate that social frailty, as a robust and multidimensional construct, effectively captures the risk of losing social resources. Thus, assessing and addressing social frailty can reduce mortality risk.
Supplementary Information
The online version contains supplementary material available at 10.1007/s11357-025-01879-0.
Keywords: Social frailty, Mortality, Cohort, Epidemiology
Introduction
Mounting epidemiological evidence highlights the critical role of social determinants in mortality prediction [1–6], encompassing constructs such as social isolation, limited social participation, and inadequate financial resources [7]. However, the fragmented individual social risk factors underscores the need for an integrative framework. Recently, social frailty has emerged as a multidimensional concept that reflects the cumulative depletion of social resources necessary to meet basic human needs. This concept has gained attention in both public health and clinical practice [8–11], offering an efficient way to integrate the prognostic impact of social factors on mortality [12], as well as disability [13], Alzheimer’s disease [14], and depression [15].
In terms of concept, social frailty is defined as a continuum of being at risk of losing, or having lost resources that are important for fulfilling one or more basic social needs during lifespan [16]. The purpose of using the term is to capture the attention of professionals using the social aspects of frailty to support older adults. It was considered as a comprehensive symptom, and constructed from multiple social aspects, including social activity (i.e., volunteering, participating in group activities), social resources (i.e., living spouses/partners), basic social needs (i.e., social support), and general resource (i.e., financial situation) [7, 13, 16]. Social frailty is a parsimonious person-level social risk [7, 12, 16], which is common and impacts approximately 18.8% (95% CI 14.9–22.7%) of community-dwelling older adults across the world [17], i.e., the pooled prevalence of social frailty was 15.2% in China [18], 21.52% in the USA [19], 16.2% in Japan, 11.6% in Spain, and 27.2% in the Netherlands [17]. Additionally, several components of social frailty were also demonstrated to be associated with adverse health outcomes, such as rarely social contact [20–23], less social activity [4, 24–26], and live alone [27–29]. Hence, social frailty and its components should be a serious concern in public health.
At present, there is growing evidence that social frailty is associated with increased risk of mortality in the older adults, such as the English Longitudinal Study of Ageing (ELSA), the Health and Retirement Study, and the Beijing Longitudinal Study of Aging [12, 30, 31]. However, these existing works were conducted to analyze the relationship between social frailty and mortality is fragmented and limited by the scarcity of data resources. Previous studies considered the relationship in enrolled participants merely restricted to the elderly population, rather than adults across a wide age spectrum. In addition, they have not examined the impact of social frailty on underlying cause of mortality. For instance, Ragusa et.al assessed social frailty in 4149 older adults aged 60 + years from ELSA, and revealed a positive association between social frailty and all-cause mortality risk [30]. Furthermore, the assessment of social frailty is essential; however, there is a lack of standardization in both its definitions and assessment methods. The Bunt classification of social frailty has primarily been used to evaluate trends in factors considered indicative of social frailty [7, 16]. In summary, there is still a considerable lack of epidemiological evidence to validate social frailty as a robust construct associated with an increased risk of mortality, particularly cause-specific mortality.
To address this knowledge gap, we first hypothesized that social frailty may be associated with increased risk of mortality in adults across a wide age spectrum, and then assessed social frailty by four social aspects. Last, we conducted a prospective cohort study to examine the potential association of social frailty, along with its components, with risk of all-cause and cause-specific mortality using data from the UK Biobank.
Methods
Study population
The UK Biobank is a large-scale, population-based, and prospective cohort study. It consisted of over 500,000 adults aged 37–73 years recruited across England, Scotland, and Wales. During the baseline period (2006 to 2010), questionnaires, physical measurements, and biological samples were used to obtain information about participants. All participants provided electronic informed consent. The UK Biobank study received approval from the National Information Governance Board for Health and Social Care and the National Health Service North West Multi-Centre Research Ethics Committee. In this cohort, a total of 421,644 participants with complete data on both components of social frailty, and death register were included and analyzed. This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cohort studies.
Social frailty
In our study, social frailty was assessed based on Bunt’s social frailty concept [16], which was widely used in many populations [30, 32–35]. The assessments of social frailty included four aspects: financial status, household status, social activity, and contacts with friends/family (Table S1). In detail, financial status was assessed using the average total household income before tax at recruitment by the question “What is the average total income before tax received by your household?” Participants were defined as financial difficulty if they response “less than £18,000”. Household status was assessed by the question “Including yourself, how many people are living together in your household (Include those who usually live in the house such as students living away from home during term, partners in the armed forces or professions such as pilots)”? Participants were classified as living alone if they response “one.” Social activity was assessed by the question “Which of the following do you attend (including sports club or gym, pub or social club, religious group, adult education class, and other group activity) once a week or more often? Participants were defined as less social activity if they response “none of the above.” Contacts with friends/family was assessed by the question “How often do you visit friends or family or have them visit you?” Participants were defined as rarely contacts with friends/family if they response “never or almost never, and once every few months.” Participants were classified as social frailty if they fulfilled two or more of the four criteria, pre-social frailty if they fulfilled one criterion, and nonsocial frailty if they did not fulfil any criteria at baseline [30, 32].
Outcomes
The primary outcome was all-cause mortality. The secondary outcome was cause-specific mortality. In the UK Biobank, dates and causes of death were obtained from the National Health Service Information Centre (England and Wales) and the National Health Service Central Register Scotland (Scotland) to 30 November 2022. We used the 10th revision of the International Statistical Classification of Diseases (ICD-10) to identify causes of death. Mortality outcomes included the following underlying causes of death: malignant neoplasms (C00-97), heart diseases (I05-09, I11, I20-28, I30-52), cerebrovascular diseases (I60-69), respiratory diseases (J00-99), Alzheimer’s disease (G30), diabetes mellitus (E10-14), and others.
Covariates
In this study, covariates included demographic characteristics, lifestyle factors, and clinical information. Demographic characteristics included age at baseline, gender, race/ethnicity, and educational status. Lifestyle factors included body mass index (BMI), smoking status, and alcohol drinking. BMI was used to divide participants into underweight (< 18 kg/m2), normal (18–25 kg/m2), overweight (25–30 kg/m2), and obese groups (> 30 kg/m2). Clinical information was obtained from self-reports, including the presence of hypertension, diabetes mellitus, heart disease, stroke, and cancer. Physical frailty status was assessed by the Fried frailty phenotype, including five components: weight loss, exhaustion, low physical activities, slow walking speed, and low grip strength [36–38]. The detail information was descripted in Table S2. Participants were classified as robust (met none of the frailty criteria), pre-physical frailty (met one or two criteria), or physical frailty (met three or more criteria) [38]. For mental health assessment, touchscreen questionnaire on psychological factors and mental health at baseline were utilized. Mental health included mood swings, miserableness, irritability, sensitivity/hurt feelings, fed-up feelings, nervous feelings, worrier/anxious feelings, tense/highly strung, worry too long after embarrassment, suffer from nerves, loneliness/isolation, guilty feelings, and risk taking. Participants who answered eight or more questions (yes/no) were included. More detail information was presented in Table S3. The total mental health complaints were calculated by adding up participant’s answers to the 13 mental health questions, where higher numbers represent more mental health-related symptoms.
Statistical analysis
First, we describe data with the mean and standard deviation (SD) or frequency (%) for continuous and categorical variables, respectively. Group differences were detected by chi-squared tests or analyses of variance (ANOVAs). Second, we utilized Cox proportional hazards models to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) of social frailty status associated with all-cause and cause-specific mortality using three models. Model 1: unadjusted; Model 2: adjusted for age, gender, education, race, smoking status, BMI category, hypertension, diabetes, heart disease, stroke, and cancer. Model 3: adjusted Model 2 and additional physical frailty status and mental health. Third, subgroups were created according to age groups (< 45, 45–64, and 65 + years), gender (male and female), BMI category (underweight, normal, overweight, and obese), race/ethnicity (White and Others), smoking status (never and ever), alcohol drinking (never and ever), and physical frailty status (robust, pre-physical frailty, and physical frailty). Stratified analysis was also conducted to examine the association between social frailty status and all-cause mortality using Model 3. Fourth, we conducted Kaplan–Meier survival to plot the association of different social frailty groups with all-cause and cause-specific mortality, respectively. Last, we also examined the combined association of social components with mortality risk. All results were considered significant at a P value < 0.05 (2-tailed). All analyses were conducted using R statistical software (version 4.2.1; www.r-project.org).
Results
Characteristics of study population at baseline
Table 1 shows the characteristics of the study population at baseline. Baseline demographic characteristics, lifestyle factors, and chronic diseases of the study population are presented in detail. At baseline, a total of 421,644 (47.45% Males, 52.55% females) participants in the UK Biobank were analyzed. The mean age of participants was 56.17 (8.09) years. Among them, 187,190 (44.39%), 150,679 (35.74%), and 83,775 (19.87%) participants were defined as non-social frailty, pre-social frailty, and social frailty, respectively.
Table 1.
Baseline characteristics of study population
| Variables | Total | Non-social frailty | Pre-social frailty | Social frailty | P value |
|---|---|---|---|---|---|
| Sample, N (%) | 421,644 | 187,190 (44.39) | 150,679 (35.74) | 83,775 (19.87) | |
| Age, years, M (SD) | 56.17 (8.09) | 55.53 (7.98) | 55.87 (8.18) | 58.15 (7.84) | < 0.001 |
| Age category, N (%) | |||||
| < 45, years | 45,739 (10.85) | 21,728 (11.61) | 17,802 (11.81) | 6209 (7.41) | < 0.001 |
| 45–64, years | 301,291 (71.46) | 137,777 (73.60) | 106,799 (70.88) | 56,715 (67.70) | |
| 65 +, years | 74,614 (17.70) | 27,685 (14.79) | 26,078 (17.31) | 20,851 (24.89) | |
| Gender, N (%) | |||||
| Male | 200,055 (47.45) | 91,164 (48.70) | 71,431 (47.41) | 37,460 (44.72) | < 0.001 |
| Female | 221,589 (52.55) | 96,026 (51.30) | 79,248 (52.59) | 46,315 (55.28) | |
| Ethnicity, N (%) | |||||
| White | 376,072 (89.38) | 169,100 (90.50) | 133,736 (88.94) | 73,236 (87.68) | < 0.001 |
| Others | 44,680 (10.62) | 17,755 (9.50) | 16,630 (11.06) | 10,295 (12.32) | |
| Educational status, N (%) | |||||
| College or above | 147,449 (35.10) | 77,213 (41.33) | 50,814 (33.87) | 19,422 (23.34) | < 0.001 |
| High school or equivalent | 210,297 (50.07) | 94,506 (50.59) | 75,613 (50.40) | 40,178 (48.29) | |
| Less than high school | 62,277 (14.83) | 15,081 (8.07) | 23,589 (15.72) | 23,607 (28.37) | |
| Alcohol drinking, N (%) | |||||
| Ever | 405,416 (96.21) | 182,148 (97.33) | 144,694 (96.08) | 78,574 (93.93) | < 0.001 |
| Never | 15,984 (3.79) | 5001 (2.67) | 5904 (3.92) | 5079 (6.07) | |
| Smoking status, N (%) | |||||
| Ever | 191,730 (45.59) | 79,453 (42.52) | 68,497 (45.57) | 43,780 (52.51) | < 0.001 |
| Never | 228,822 (54.41) | 107,411 (57.48) | 81,812 (54.43) | 39,599 (47.49) | |
| Body mass index categories, N (%) | |||||
| Underweight (< 18 kg/m2) | 2097 (0.50) | 703 (0.38) | 730 (0.49) | 664 (0.80) | < 0.001 |
| Normal (18–25 kg/m2) | 137,161 (32.68) | 64,118 (34.37) | 47,932 (31.96) | 25,111 (30.21) | |
| Overweight (25–30 kg/m2) | 179,200 (42.70) | 82,712 (44.33) | 63,578 (42.39) | 32,910 (39.59) | |
| Obese (> 30 kg/m2) | 101,220 (24.12) | 39,032 (20.92) | 37,753 (25.17) | 24,435 (29.40) | |
| Physical frailty status, N (%) | |||||
| Non-physical frailty | 222,508 (55.52) | 112,436 (62.43) | 77,614 (54.20) | 32,458 (41.90) | < 0.001 |
| Pre-physical frailty | 162,589 (40.57) | 64,586 (35.86) | 60,137 (42.00) | 37,866 (48.88) | |
| Physical frailty | 15,676 (3.91) | 3091 (1.72) | 5444 (3.80) | 7141 (9.22) | |
| Chronic diseases, N (%) | |||||
| Hypertension | 99,374 (23.57) | 40,175 (21.46) | 35,630 (23.65) | 23,569 (28.13) | < 0.001 |
| Diabetes mellitus | 21,179 (5.02) | 6836 (3.65) | 7728 (5.13) | 6615 (7.90) | < 0.001 |
| Heart disease | 9484 (2.25) | 3156 (1.69) | 3346 (2.22) | 2982 (3.56) | < 0.001 |
| Stroke | 4989 (1.18) | 1600 (0.85) | 1742 (1.16) | 1647 (1.97) | < 0.001 |
| Cancer | 31,787 (7.54) | 13,091 (6.99) | 11,137 (7.39) | 7559 (9.02) | < 0.001 |
| Mental health score, M (SD) | 0.35 (0.26) | 0.32 (0.24) | 0.35 (0.25) | 0.40 (0.27) | < 0.001 |
| Items of social frailty, N (%) | |||||
| Financial difficulty | 95,474 (22.64) | 0 (0.00) | 33,602 (22.30) | 61,872 (73.85) | < 0.001 |
| Less social activity | 126,700 (30.05) | 0 (0.00) | 74,697 (49.57) | 52,003 (62.07) | < 0.001 |
| Rarely contacts with friends/family | 34,221 (8.12) | 0 (0.00) | 13,892 (9.22) | 20,329 (24.27) | < 0.001 |
| Live alone | 81,351 (19.29) | 0 (0.00) | 28,488 (18.91) | 52,863 (63.10) | < 0.001 |
Association between social frailty status and mortality
During a median follow-up period of 13.75 years, 35,480 individuals died. The results of Cox proportional hazard analyses between social frailty status and the risk of mortality were presented in Table 2. In the multivariable analysis, compared to individuals with non-social frailty, those with pre-social frailty (HR 1.13, 95% CI 1.10–1.16) had higher risk of all-cause mortality, as well as mortality due to malignant neoplasms (HR 1.09, 95% CI 1.05–1.13), heart diseases (HR 1.19, 95% CI 1.11–1.29), respiratory diseases (HR 1.29, 95% CI 1.15–1.45), and others (HR 1.17, 95% CI 1.10–1.23). Meanwhile, individuals with social frailty had higher risk of all-cause mortality (HR 1.53, 95% CI 1.49–1.58) and cause-specific mortality, including malignant neoplasms (HR 1.37, 95% CI 1.31–1.42), heart diseases (HR 1.90, 95% CI 1.75–2.06), cerebrovascular diseases (HR 1.46, 95% CI 1.27–1.69), respiratory diseases (HR 2.10, 95% CI 1.87–2.37), diabetes mellitus (HR 2.43, 95% CI 1.66–3.56), and others (HR 1.75, 95% CI 1.65–1.86).
Table 2.
Association of social frailty status with all-cause and cause-specific mortality
| Model 1 | Model 2 | Model 3 | |||||
|---|---|---|---|---|---|---|---|
| Event/N (%) | HR (95% CI) | P value | HR (95% CI) | P value | HR (95% CI) | P value | |
| All-cause mortality | |||||||
| Non-social frailty | 11,633/187,190 (6.21) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| Pre-social frailty | 12,058/150,679 (8.00) | 1.30 (1.27–1.34) | < 0.001 | 1.17 (1.14–1.20) | < 0.001 | 1.13 (1.10–1.16) | < 0.001 |
| Social frailty | 11,789/83,775 (14.07) | 2.37 (2.31–2.43) | < 0.001 | 1.70 (1.66–1.75) | < 0.001 | 1.53 (1.49–1.58) | < 0.001 |
| Malignant neoplasms | |||||||
| Non-social frailty | 6284/181,841 (3.46) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| Pre-social frailty | 5975/144,596 (4.13) | 1.20 (1.16–1.25) | < 0.001 | 1.11 (1.07–1.15) | < 0.001 | 1.09 (1.05–1.13) | < 0.001 |
| Social frailty | 5042/77,028 (6.55) | 1.93 (1.86–2.00) | < 0.001 | 1.44 (1.39–1.50) | < 0.001 | 1.37 (1.31–1.42) | < 0.001 |
| Heart diseases | |||||||
| Non-social frailty | 1413/176,970 (0.80) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| Pre-social frailty | 1660/140,281 (1.18) | 1.49 (1.39–1.60) | < 0.001 | 1.26 (1.17–1.35) | < 0.001 | 1.19 (1.11–1.29) | < 0.001 |
| Social frailty | 1898/73,884 (2.57) | 3.26 (3.04–3.49) | < 0.001 | 2.22 (2.06–2.39) | < 0.001 | 1.90 (1.75–2.06) | < 0.001 |
| Cerebrovascular diseases | |||||||
| Non-social frailty | 498/176,055 (0.28) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| Pre-social frailty | 496/139,117 (0.36) | 1.26 (1.12–1.43) | < 0.001 | 1.12 (0.99–1.28) | 0.073 | 1.10 (0.96–1.25) | 0.168 |
| Social frailty | 501/72,487 (0.69) | 2.46 (2.17–2.78) | < 0.001 | 1.62 (1.41–1.85) | < 0.001 | 1.46 (1.27–1.69) | < 0.001 |
| Respiratory diseases | |||||||
| Non-social frailty | 571/176,128 (0.32) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| Pre-social frailty | 800/139,421 (0.57) | 1.78 (1.60–1.98) | < 0.001 | 1.45 (1.29–1.62) | < 0.001 | 1.29 (1.15–1.45) | < 0.001 |
| Social frailty | 1100/73,086 (1.51) | 4.69 (4.24–5.18) | < 0.001 | 2.85 (2.55–3.18) | < 0.001 | 2.10 (1.87–2.37) | < 0.001 |
| Alzheimer’s disease | |||||||
| Non-social frailty | 211/175,768 (0.12) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| Pre-social frailty | 222/138,843 (0.16) | 1.34 (1.11–1.61) | 0.002 | 1.17 (0.97–1.42) | 0.108 | 1.13 (0.92–1.38) | 0.235 |
| Social frailty | 168/72,154 (0.23) | 1.95 (1.59–2.39) | < 0.001 | 1.22 (0.98–1.52) | 0.076 | 1.09 (0.86–1.37) | 0.489 |
| Diabetes mellitus | |||||||
| Non-social frailty | 48/175,605 (0.03) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| Pre-social frailty | 88/138,709 (0.06) | 2.33 (1.64–3.31) | < 0.001 | 1.69 (1.17–2.43) | 0.005 | 1.44 (0.99–2.10) | 0.058 |
| Social frailty | 113/72,099 (0.16) | 5.76 (4.11–8.07) | < 0.001 | 2.83 (1.97–4.08) | < 0.001 | 2.43 (1.66–3.56) | < 0.001 |
| Others | |||||||
| Non-social frailty | 2608/178,165 (1.46) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| Pre-social frailty | 2817/141,438 (1.99) | 1.37 (1.30–1.44) | < 0.001 | 1.23 (1.17–1.30) | < 0.001 | 1.17 (1.10–1.23) | < 0.001 |
| Social frailty | 2967/74,953 (3.96) | 2.75 (2.61–2.90) | < 0.001 | 2.03 (1.92–2.15) | < 0.001 | 1.75 (1.65–1.86) | < 0.001 |
Model 1, crude model; Model 2, adjusted for age, gender, body Mass index, race, educational levels, smoking status, alcohol drinking, hypertension, diabetes, heart disease, stroke, and cancer; Model 3, adjusted for Model 2 and additional physical frailty status and mental health
In further analyses, we conducted stratified analyses across various strata defined by age groups, gender, BMI category, race/ethnicity, smoking status, alcohol drinking, and physical frailty status. Similar findings of the associations of pre-social frailty and social frailty with risk of all-cause mortality were revealed (Fig. 1), suggesting that individuals with pre-social frailty or social frailty had significantly higher risks of mortality than those with non-social frailty, independent of socioeconomic status, lifestyles, chronic diseases, and physical frailty status. Kaplan–Meier survival plots demonstrated that individuals with pre-social frailty or social frailty both had significantly increased cumulative all-cause mortality than those without (P value < 0.0001, Fig. 2), and similar patterns were observed for cause-specific mortality, including malignant neoplasms, heart diseases, cerebrovascular diseases, respiratory diseases, and diabetes mellitus (P value < 0.0001, Fig. 2).
Fig. 1.
Associations of pre-social frailty and social frailty with all-cause mortality in subgroups. Social robust people were used as the reference group for each analysis. All models were adjusted for age, gender, body mass index, race, educational levels, smoking status, alcohol drinking, hypertension, diabetes, heart disease, stroke, cancer, and physical frailty. HR, hazard ratio; CI, confidence interval; HS, hihger school
Fig. 2.
Kaplan–Meier survival curves for all-cause and cause-specific mortality according to social frailty status
Association between components of social frailty and mortality
Additionally, we analyzed the relationships between four components of social frailty and risks of all-cause and cause-specific mortality (Table 3). The components of social frailty, including financial difficulty (HR 1.39, 95% CI 1.35–1.42), less social activity (HR 1.09, 95% CI 1.06–1.11), rarely contacts with friends/family (HR 1.17, 95% CI 1.13–1.22), and live alone (HR 1.39, 95% CI 1.36–1.42), were also associated with all-cause mortality. For cause-specific mortality, financial difficulty, and live alone were associated with mortality caused by malignant neoplasms, heart diseases, cerebrovascular diseases, respiratory diseases, and others (P value < 0.05). Less social activity was associated with mortality caused by malignant neoplasms, respiratory diseases, and others (P value < 0.05). Rarely contacts with friends/family were associated with mortality caused by malignant neoplasms, heart diseases, respiratory diseases, and others (P value < 0.05). However, we did not find any significant association of the four components with mortality caused by Alzheimer’s disease (P value > 0.05).
Table 3.
Association of components of social frailty with all-cause and cause-specific mortality
| Model 1 | Model 2 | Model 3 | |||||
|---|---|---|---|---|---|---|---|
| Event/N (%) | HR (95% CI) | P value | HR (95% CI) | P value | HR (95% CI) | P value | |
| All-cause mortality | |||||||
| Financial difficulty | 14,351/95,474 (15.03) | 2.43 (2.38–2.48) | < 0.001 | 1.50 (1.46–1.54) | < 0.001 | 1.39 (1.35–1.42) | < 0.001 |
| Less social activity | 11,672/126,700 (9.21) | 1.15 (1.13–1.18) | < 0.001 | 1.16 (1.13–1.18) | < 0.001 | 1.09 (1.06–1.11) | < 0.001 |
| Rarely contacts with friends/family | 3357/34,221 (9.81) | 1.20 (1.16–1.24) | < 0.001 | 1.24 (1.19–1.28) | < 0.001 | 1.17 (1.13–1.22) | < 0.001 |
| Live alone | 9953/81,351 (12.23) | 1.68 (1.64–1.72) | < 0.001 | 1.47 (1.43–1.50) | < 0.001 | 1.39 (1.36–1.42) | < 0.001 |
| Malignant neoplasms | |||||||
| Financial difficulty | 6108/87,231 (7.00) | 2.01 (1.95–2.08) | < 0.001 | 1.30 (1.25–1.35) | < 0.001 | 1.25 (1.21–1.30) | < 0.001 |
| Less social activity | 5567/120,595 (4.62) | 1.12 (1.08–1.15) | < 0.001 | 1.15 (1.11–1.18) | < 0.001 | 1.11 (1.07–1.15) | < 0.001 |
| Rarely contacts with friends/family | 1471/32,335 (4.55) | 1.07 (1.02–1.13) | 0.011 | 1.15 (1.09–1.21) | < 0.001 | 1.11 (1.05–1.18) | < 0.001 |
| Live alone | 4332/75,730 (5.72) | 1.46 (1.41–1.51) | < 0.001 | 1.28 (1.23–1.32) | < 0.001 | 1.24 (1.20–1.29) | < 0.001 |
| Heart diseases | |||||||
| Financial difficulty | 2246/83,369 (2.69) | 3.07 (2.90–3.24) | < 0.001 | 1.76 (1.65–1.88) | < 0.001 | 1.57 (1.47–1.68) | < 0.001 |
| Less social activity | 1672/116,700 (1.43) | 1.20 (1.13–1.27) | < 0.001 | 1.14 (1.08–1.22) | < 0.001 | 1.05 (0.98–1.12) | 0.138 |
| Rarely contacts with friends/family | 584/31,448 (1.86) | 1.53 (1.41–1.67) | < 0.001 | 1.44 (1.32–1.58) | < 0.001 | 1.34 (1.22–1.47) | < 0.001 |
| Live alone | 1599/72,997 (2.19) | 2.08 (1.96–2.21) | < 0.001 | 1.90 (1.79–2.02) | < 0.001 | 1.75 (1.64–1.87) | < 0.001 |
| Cerebrovascular diseases | |||||||
| Financial difficulty | 655/81,778 (0.80) | 2.92 (2.64–3.24) | < 0.001 | 1.58 (1.40–1.77) | < 0.001 | 1.45 (1.28–1.64) | < 0.001 |
| Less social activity | 433/115,461 (0.38) | 0.96 (0.86–1.08) | 0.519 | 1.02 (0.91–1.15) | 0.689 | 0.99 (0.88–1.11) | 0.853 |
| Rarely contacts with friends/family | 125/30,989 (0.40) | 1.06 (0.88–1.27) | 0.562 | 1.19 (0.99–1.44) | 0.065 | 1.12 (0.92–1.36) | 0.251 |
| Live alone | 445/71,843 (0.62) | 1.87 (1.67–2.09) | < 0.001 | 1.53 (1.36–1.71) | < 0.001 | 1.47 (1.30–1.65) | < 0.001 |
| Respiratory diseases | |||||||
| Financial difficulty | 1323/82,446 (1.60) | 4.31 (3.98–4.66) | < 0.001 | 2.13 (1.95–2.33) | < 0.001 | 1.73 (1.57–1.90) | < 0.001 |
| Less social activity | 983/116,011 (0.85) | 1.56 (1.44–1.69) | < 0.001 | 1.52 (1.40–1.65) | < 0.001 | 1.27 (1.16–1.38) | < 0.001 |
| Rarely contacts with friends/family | 251/31,115 (0.81) | 1.31 (1.15–1.49) | < 0.001 | 1.35 (1.18–1.55) | < 0.001 | 1.19 (1.03–1.36) | 0.018 |
| Live alone | 845/72,243 (1.17) | 2.29 (2.10–2.49) | < 0.001 | 1.94 (1.78–2.11) | < 0.001 | 1.66 (1.52–1.82) | < 0.001 |
| Alzheimer’s disease | |||||||
| Financial difficulty | 248/81,371 (0.30) | 2.64 (2.24–3.10) | < 0.001 | 1.21 (1.01–1.45) | 0.038 | 1.13 (0.94–1.36) | 0.201 |
| Less social activity | 182/115,210 (0.16) | 1.03 (0.86–1.22) | 0.748 | 1.19 (1.00–1.42) | 0.055 | 1.12 (0.93–1.35) | 0.222 |
| Rarely contacts with friends/family | 48/30,912 (0.16) | 1.01 (0.75–1.35) | 0.955 | 1.31 (0.97–1.77) | 0.075 | 1.28 (0.94–1.74) | 0.118 |
| Live alone | 131/71,529 (0.18) | 1.23 (1.02–1.50) | 0.035 | 0.94 (0.77–1.15) | 0.569 | 0.88 (0.71–1.08) | 0.228 |
| Diabetes mellitus | |||||||
| Financial difficulty | 146/81,269 (0.18) | 5.33 (4.14–6.85) | < 0.001 | 2.66 (2.01–3.52) | < 0.001 | 2.20 (1.64–2.95) | < 0.001 |
| Less social activity | 97/115,125 (0.08) | 1.51 (1.17–1.94) | 0.002 | 1.16 (0.89–1.51) | 0.271 | 1.11 (0.84–1.46) | 0.456 |
| Rarely contacts with friends/family | 34/30,898 (0.11) | 1.83 (1.27–2.62) | 0.001 | 1.42 (0.97–2.07) | 0.073 | 1.36 (0.92–2.02) | 0.126 |
| Live alone | 87/71,485 (0.12) | 2.37 (1.83–3.07) | < 0.001 | 1.76 (1.34–2.30) | < 0.001 | 1.62 (1.22–2.15) | 0.001 |
| Others | |||||||
| Financial difficulty | 3625/84,748 (4.28) | 2.82 (2.70–2.94) | < 0.001 | 1.79 (1.70–1.88) | < 0.001 | 1.60 (1.52–1.68) | < 0.001 |
| Less social activity | 2738/117,766 (2.32) | 1.14 (1.09–1.20) | < 0.001 | 1.16 (1.10–1.21) | < 0.001 | 1.06 (1.01–1.11) | 0.020 |
| Rarely contacts with friends/family | 844/31,708 (2.66) | 1.29 (1.20–1.39) | < 0.001 | 1.31 (1.22–1.41) | < 0.001 | 1.21 (1.13–1.31) | < 0.001 |
| Live alone | 2514/73,912 (3.40) | 1.88 (1.79–1.96) | < 0.001 | 1.69 (1.61–1.77) | < 0.001 | 1.57 (1.50–1.65) | < 0.001 |
Model 1, crude model; Model 2, adjusted for age, gender, body Mass index, race, educational levels, smoking status, alcohol drinking, hypertension, diabetes, heart disease, stroke, and cancer; Model 3, Adjusted for Model 2 and additional physical frailty status and mental health
Association of single andcombined social factors with mortality
Last, we examined the association of single and combined components of social frailty with all-cause mortality. In the fully adjusted model, compared to individuals with no unfavorable social factors, those with one, two, three, and four unfavorable social factors had higher risks of all-cause mortality (Table 4). Increasing numbers of unfavorable social factors were dose‐dependently associated with an increased risk of all-cause mortality. Additionally, we also examined the association of single and combined social factors with cause-specific mortality and found many statistics association between these social factors with mortality caused by malignant neoplasms, heart diseases, cerebrovascular diseases, respiratory diseases, diabetes, Alzheimer’s disease, and others (Tables S4-S10).
Table 4.
Association of single and combined social factors with all-cause mortality
| Model 1 | Model 2 | Model 3 | |||||
|---|---|---|---|---|---|---|---|
| Event/N (%) | HR (95% CI) | P value | HR (95% CI) | P value | HR (95% CI) | P value | |
| No unfavorable social factors | 11,633/187,190 (6.21) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) | 1 (Ref) |
| FD only | 4313/33,602 (12.84) | 2.14 (2.06–2.21) | < 0.001 | 1.27 (1.22–1.33) | < 0.001 | 1.22 (1.17–1.27) | < 0.001 |
| LSA only | 4777/74,697 (6.40) | 1.03 (1.00–1.07) | 0.060 | 1.09 (1.05–1.13) | < 0.001 | 1.04 (1.01–1.08) | 0.019 |
| RC only | 913/13,892 (6.57) | 1.06 (0.99–1.14) | 0.075 | 1.13 (1.06–1.21) | < 0.001 | 1.11 (1.03–1.19) | 0.00 |
| LA only | 2055/28,488 (7.21) | 1.17 (1.12–1.23) | < 0.001 | 1.23 (1.18–1.29) | < 0.001 | 1.21 (1.15–1.27) | < 0.001 |
| FD + LSA | 2646/17,818 (14.85) | 2.51 (2.41–2.62) | < 0.001 | 1.55 (1.48–1.62) | < 0.001 | 1.38 (1.31–1.45) | < 0.001 |
| FD + RC | 352/2472 (14.24) | 2.42 (2.18–2.69) | < 0.001 | 1.54 (1.38–1.72) | < 0.001 | 1.40 (1.24–1.57) | < 0.001 |
| FD + LA | 3853/24,835 (15.51) | 2.62 (2.53–2.72) | < 0.001 | 1.73 (1.66–1.80) | < 0.001 | 1.57 (1.51–1.64) | < 0.001 |
| LSA + RC | 599/8698 (6.89) | 1.12 (1.03–1.21) | 0.008 | 1.23 (1.13–1.34) | < 0.001 | 1.13 (1.03–1.23) | 0.007 |
| LSA + LA | 799/9755 (8.19) | 1.34 (1.25–1.44) | < 0.001 | 1.44 (1.34–1.55) | < 0.001 | 1.37 (1.27–1.47) | < 0.001 |
| RC + LA | 212/2249 (9.43) | 1.56 (1.37–1.79) | < 0.001 | 1.67 (1.46–1.92) | < 0.001 | 1.57 (1.36–1.81) | < 0.001 |
| FD + LSA + RC | 294/1924 (15.28) | 2.61 (2.32–2.93) | < 0.001 | 1.74 (1.54–1.96) | < 0.001 | 1.47 (1.29–1.67) | < 0.001 |
| FD + LSA + LA | 2047/11,038 (18.55) | 3.21 (3.06–3.36) | < 0.001 | 2.11 (2.01–2.23) | < 0.001 | 1.80 (1.71–1.91) | < 0.001 |
| FD + RC + LA | 477/2216 (21.53) | 3.82 (3.49–4.19) | < 0.001 | 2.32 (2.11–2.55) | < 0.001 | 1.98 (1.78–2.19) | < 0.001 |
| LSA + RC + LA | 141/1201 (11.74) | 1.99 (1.68–2.35) | < 0.001 | 2.09 (1.76–2.47) | < 0.001 | 1.90 (1.59–2.26) | < 0.001 |
| FD + LSA + RC + LA | 369/1569 (23.52) | 4.27 (3.85–4.73) | < 0.001 | 2.84 (2.55–3.16) | < 0.001 | 2.30 (2.05–2.58) | < 0.001 |
| Per additional unfavorable social factors | 4313/33,602 (12.84) | 2.14 (2.06–2.21) | < 0.001 | 1.27 (1.22–1.33) | < 0.001 | 1.22 (1.17–1.27) | < 0.001 |
FD, financial difficulty; LSA, less social activity; RC, Rarely contacts with friends/family; LA, live alone
Model 1, crude model; Model 2, adjusted for age, gender, body Mass index, race, educational levels, smoking status, alcohol drinking, hypertension, diabetes, heart disease, stroke, and cancer. Model 3, adjusted for Model 2 and additional physical frailty status and mental health
Discussion
In this study, we assessed social frailty integrated from four components: financial difficulty, live alone, less social activity, and rarely contacts with friends/family. We examined the association between social frailty status and mortality using data from 421,644 adults aged 37–73 years in the UK Biobank. We identified that, compared to those with non-social frailty, individuals with pre-social frailty and social frailty were at a higher risk of all-cause and cause-specific mortality in adults across a wide age spectrum, even after adjusting for socioeconomic status, lifestyles, chronic diseases, physical frailty status, and mental health.
To our knowledge, this is the largest study to examine the association of social frailty status with all-cause and cause-specific mortality in adults across a wide age spectrum. Nonetheless, previous studies had assessed social frailty based on Bunt’s social frailty concept, and examined the association between social frailty status and all-cause mortality in the elderly population [30, 32]. For example, Ragusa et. al included 4149 older adults aged 60 + years from ELSA, and revealed that social frailty (HR 1.31, 95% CI 1.04–1.64), but not pre-social frailty (HR 1.22, 95% CI 0.97–1.53), was associated with higher risk of all-cause mortality risk during the 10-year follow-up period [30]. Yamada et.al recruited 6603 community-dwelling adults aged 65 + years in Japan, and found that individuals with pre-social frailty (HR 1.16, 95% CI 1.16–1.41) and social frailty (HR 1.71, 95% CI 1.54–1.90) had higher risk of mortality than those with non-social frailty during the 6-year follow-up period [32]. Additionally, several different assessment measurements of social frailty (such as the Shah social frailty Index [12], the HALFT scale [31], and others [39, 40]) were also reported to be associated with increased mortality risk in the elderly population, compared with non-social frailty. However, the existing literatures had merely focused on older adults aged 60 + years, it is unclear whether the association between social frailty and mortality is remained in adults aged younger than 60 years. In our study, this was the largest and first study involving adults younger than age 65 years (45,739 individuals aged less than 45 years, and 301,291 aged 45–64 years), and showed positive association between social frailty and mortality. In addition, previous studies merely examined the impact of social frailty on all-cause mortality, but not on underlying cause of mortality. In this study, we identified causes of death in the UK Biobank, and for the first time, revealed the important role of social frailty on mortality resulting from malignant neoplasms, heart disease, cerebrovascular diseases, respiratory diseases, diabetes mellitus, and others. In summary, our findings suggested assessment of social frailty might help to identify high-risk of mortality in adults across a wide age spectrum.
Strengths and limitations
Several strengths were presented in our study. We conducted this study in a prospective cohort study with a longer follow-up period and largest samples (included 421,644 adults aged 37–73 years) in the UK Biobank, which increased the credibility of our results. We used the overwhelming data from the UK Biobank that favored us considering a large confounder factor, especially the physical frailty status. In addition, the assessment of social frailty in our study was based on four simple questions, suggesting that social frailty could be simply and conveniently assessed in general population, as well as in clinal practice. However, limitations in this study should also be noted. First, our study was an observational study; the association between social frailty and mortality merely reflects a correlational but not a causal relationship. Second, at present, several assessment tools of social frailty have been developed (e.g., the Makizako Social Frailty [13], the Shah social frailty Index [12], the HALFT scale [31], Tilburg Frailty Indicator [41], and others [39, 40]), but international consensus concerning the criteria for determining social frailty is lacking yet [8]. Since we assessed social frailty based on Bunt’s social frailty concept, further studies with different assessments of social frailty should be conducted to validate our findings. Last, our study mainly included White participants (88.91%), and the associations we observed between social frailty and mortality are warranted replicated in other ethnicities.
In conclusion, social frailty, which integrated from four components: financial difficulty, live alone, less social activity, and rarely contacts with friends/family, was strongly and independently associated with increased risk of all-cause and cause-specific mortality in adults across a wide age spectrum, independent of sociodemographic factors, lifestyles, chronic diseases, and physical frailty status. Our findings suggested that integrating social frailty assessment into the primary prevention of mortality may favor the identification of high-risk individuals not only in older adults (≥ 65 years), but also in adults younger than 65 years. Further studies involving in diverse ethnic populations and different measurement of social frailty are warranted to confirm our findings and elucidate the underlying mechanisms.
Supplementary Information
Below is the link to the electronic supplementary material.
(DOCX 59.1 KB)
Acknowledgements
We thank the workers, researchers, and participants involved in the UK Biobank.
Author contribution
Dr. Hui Zhang had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Conceptualization: ZH, HM; Methodology: HM, JS, HZ.
Investigation: ZH, HM, LY, WS, ZX; Visualization: HM, LX, WS; Supervision: ZH, JS; Writing original draft: HM, JS, HZ; Writing review and editing: ZH, HM, JS.
Funding
This work was supported by grants from the National Natural Science Foundation of China (82301768, 32300533, 32100510), the Key Discipline Construction Project of Pudong Health and Family Planning Commission of Shanghai (PWZxk2022-01), the Shanghai Sailing Program (23YF1430500), the Scientific Research Foundation provided by Pudong Hospital affiliated to Fudan University (YJYJRC202202), and the Talents Training Program of Pudong Hospital affiliated to Fudan University (YQ202201).
Data Availability
Data from the UK Biobank are available on application at www.ukbiobank.ac.uk/register-apply. This research was conducted using the UK Biobank resource under application number 103791. All other data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials.
Declarations
Ethical statement
The North West Multi-Centre Research Ethics Committee approved the collection and use of the UK Biobank data.
Consent for publication
All participants provided written informed consent. Institutional review board approval was waived for this analysis because of the publicly available and deidentified data.
Competing Interests
The authors declare no competing interests.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Meng Hao and Zixin Hu contributed equally to this work.
Contributor Information
Meng Hao, Email: haombio@gmail.com.
Shuai Jiang, Email: zhiyusang@163.com.
Hui Zhang, Email: zhanghui2939@163.com, Email: h_zhang@fudan.edu.cn.
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Associated Data
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Data Availability Statement
Data from the UK Biobank are available on application at www.ukbiobank.ac.uk/register-apply. This research was conducted using the UK Biobank resource under application number 103791. All other data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials.