2. Materials and Methods
The search strategy
Although the frequency of frailty and loneliness is high, the mechanism by which loneliness influences the progression of frailty remains incompletely elucidated. To assess the link between frailty and loneliness, we conducted a search accessing Index Medicus and PubMed in September–December 2023 (
Table 1).
The following search strategy was used: loneliness AND frailty AND ( fulltext:(“1” OR “1”) AND mj:(“Frail Elderly” OR “Aging” OR “Geriatric Assessment” OR “Health of the Elderly” OR “Quality of Life” OR “Activities of Daily Living” OR “Primary Health Care” OR “Risk Factors” OR “Prevalence”) AND la:(“en”)) AND (year_cluster:[2013 TO 2023]).
The inclusion criterion was any study (either descriptive or analytic) enrolling adult patients over the age of 60 diagnosed with frailty (either using Clinical Diagnostic Criteria for frailty or other validated diagnostic scales or instruments) and/or loneliness.
Studies were excluded if they were in a language other than English or if the full text was not freely available.
Studies not identified using this search strategy that were subsequently identified and met the mentioned inclusion criterion were also included in our study.
Study appraisal
The first evaluation was made by reading the title and abstract. The subsequent evaluation of the remaining articles involved reading the full text to determine eligibility for inclusion in our study. Duplicate articles were excluded.
Data regarding the study populations, as well as the loneliness and fragility assessment and approach, were extracted. We took descriptive or analytic studies enrolling adult patients diagnosed with frailty and/or loneliness into consideration.
During data extraction, we took into account the fact that, in the literature, in order to implement intervention strategies that are as suitable as possible for the target groups, different methods for assessing loneliness and fragility have been proposed. Furthermore, loneliness and frailty have been classified over time according to various criteria. For instance, loneliness can be assessed via self-reported scales that capture feelings of social isolation, emotional distress, and lack of companionship. Regarding the risk factors that can also represent the starting point for intervention plans, loneliness can be addressed through increasing social support, increasing opportunities for social interaction, improving social skills, and socio-cognitive training [
19].
Frailty, on the other hand, can be measured using multi-dimensional instruments that assess physical function, cognition, nutrition, and other relevant domains, such as the frailty index or frailty phenotype (Clinical Frailty Scale [
15], Edmonton Frail Scale (
https://edmontonfrailscale.org/validation-scale-and-spread), FRAIL scale (
https://www.bgs.org.uk/sites/default/files/content/attachment/2018-07-05/rockwood_cfs.pdf), INTER-FRAIL (jgs13029-sup-0001-TableS1-S2.docx) Prisma-7, Sherbrooke Postal Questionnaire (
https://www2.gov.bc.ca/assets/gov/health/practitioner-pro/bc-guidelines/frailty-prisma7.pdf), Short Physical Performance Battery (
https://geriatrictoolkit.missouri.edu/SPPB-Score-Tool.pdf ), and Study of Osteoporotic Fractures Index (
https://agingresearchbiobank.nia.nih.gov/studies/sof/ ) or newer scales, for example, Kihon's list(
http://jssf.umin.jp/pdf/Kihon%20Checklist.pdf ) [
18].
Taking all these aspects into account, we decided to assess any study (either descriptive or analytic) enrolling adult patients diagnosed with frailty—either using Clinical Diagnostic Criteria for frailty, Fried frailty phenotype assessment, the Short Physical Performance Battery (SPPB), the Frailty Deficit Index (FDI), the Tilburg Frailty Indicator (TFI), Clinical-Functional Vulnerability Index-20 (IVCF-20; instrumental daily living activity, cognition, mood, mobility, communication, and multiple comorbidities), the Edmonton Frail Scale, or the Comprehensive Geriatric Assessment (CGA)—and/or loneliness.
3. Results
Starting from the association between frailty and loneliness, 213 articles were selected. After reading the titles and abstracts, 74 studies were excluded. The full texts of all remaining articles were read, and two independent authors (E.B. and A.C.G.) evaluated and included the eligible articles. Different opinions were discussed with all the other authors until a consensus was reached. Finally, only 18 studies were analyzed (
Table S1).
Through examining the relationship between loneliness and frailty, our aim was to shed light on possible ways in which social isolation may contribute to physical decline and increased vulnerability among older adults. We set out to explore the
epidemiology of loneliness and frailty,
risk factors and potential consequences,
classification systems, and discussions of
the impact of loneliness on frailty [
8,
24].
Several studies have examined the prevalence and incidence of loneliness and frailty among older adults. For example, a study by Clegg et al. [
8] found that approximately 10–40% of older adults experience moderate to severe loneliness. Regarding frailty, another study [
25] showed that the prevalence of frailty among community-dwelling older adults ranges from 4% to 59%, depending on the diagnostic criteria used. Another study estimates that approximately 25–50% of people over 85 are frail [
26]. It is important to specify that up to 75% of these people may not present pronounced frailty, highlighting the importance of studying the etiology of frailty and methods for its prevention [
8]. Sha et al. have reported that greater loneliness was related to an increased risk of worsening frailty and remaining frail [
13]. Moreover, it seems that elderly men with a high level of loneliness had a worse degradation of clinical status through frailty compared to elderly women [
13].
Although frailty is chronologically and biologically related to age, occurs with a higher prevalence in women than in men, and is usually associated with chronic diseases [
27], there is great heterogeneity in terms of the
prevalence and degree of impairment associated with frailty in groups of people who fall under the same clinical–biological criteria. The higher prevalence of frailty among women may be explained by having, on average, lower body mass and lower muscle strength. In addition, it should be taken into account that women live longer on average than men, and the association of increased age with frailty has been demonstrated in various studies [
27]. The association of frailty with chronic diseases—with up to 66% of older adults suffering from at least two chronic conditions [
25]—calls for more effective prevention strategies to reduce potential risks. Due to the increasing incidence of obesity in adults, particularly abdominal obesity, it is necessary to pay more attention, as this condition is associated with an increased risk of frailty through the predisposition to pro-inflammatory status, cardiovascular diseases, and hormonal imbalances. This co-association of several emerging factors with basic diseases of the individual is called multi-morbidity, and there are many studies that attest to the cause–effect relationship between this condition and the association of frailty with mortality [
28]. However, a study by Zucchelli et al. [
26], based on a population aged over 60 years established in Stockholm, Sweden, showed an increased mortality risk in pre-frail and frail individuals, compared to those in whom these conditions are not present, even in the absence of multiple chronic pathologies.
Damluji et al. [
29] found that pre-frailty and physical frailty phenotypes were associated with a high risk of major adverse cardiovascular events and mortality, despite rigorous control of cardiovascular risk factors, during 6 years of follow-up. Their conclusion was that efforts should be made to integrate frailty assessment as part of primary cardiovascular prevention programs for older adults at risk of cardiovascular disease, which are essential in daily cardiovascular clinical practice. As the growth of the adult population has been recorded worldwide, it is imperative to evaluate the efficiency and effectiveness of programs to maintain active status through promoting physical exercise, adequate nutrition, and cognitive training to prevent or even reverse frailty in patients with cardiovascular risk [
29].
These factors can be considered
intrinsic, but there are also
extrinsic variables, mainly included under the name of social vulnerability (relating to socio-economic level, social relations, and family support) which, in the context of their decrease, have been associated with greater fragility and an increased rate of in-hospital death [
19].
According to a 2020 report by the National Health and Aging Trends Study, in the United States, a significant number of older adults (approximately 7.7 million people) experienced loneliness and social isolation [
30]. Before the Coronavirus Disease 2019 (COVID-19) pandemic, about 24% of adults aged 65 and older living in the community were socially isolated, and 4% of them were severely isolated [
30]. Some studies have pointed out that approximately one in four community-dwelling adults are socially isolated. It seems that, among older adults, risk factors for social isolation include male gender, lower income, and lower educational attainment [
28,
30,
31].
During the COVID-19 pandemic, some studies showed that there were no significant changes at the level of the elderly population regarding isolation, with the elderly feeling social isolation less acutely compared to other population groups [
31].
According to a study based on data from the U.S. Health and Retirement Study, 43% of Americans aged 60 and older reported feeling lonely [
11]. Additionally, a survey conducted by The American Association of Retired Persons (AARP) found that 35% of adults over the age of 45 feel lonely [
32].
In Europe, around 20% of older people experience loneliness. This means that 1 in 5 older people feel a sense of isolation and lack of social connection. The percentage varies by country, with higher levels of loneliness in countries such as Sweden and Norway (over 25%) and lower levels in Spain and Greece (under 15%), underscoring the scale of the problem and the significant social impact on older people. It is important to pay attention to this aspect and develop prevention and intervention strategies to combat loneliness and promote well-being among the older population [
33].
Older people who feel lonely and socially isolated have certain characteristics in common. These include older age, single status, male gender, low education, and low income [
33]. Social isolation increases the risk of loneliness and can be assessed using five indicators:
Status of being unmarried or non-cohabitant, living without another family member in the same house;
Less than monthly contact with own children who do not live in the same house as them (physically, in writing, or by phone);
Less than monthly contact with other family members who do not live in the same house as them (physically, in writing, or by telephone);
Less than monthly contact with friends (physical, written, or by phone) who do not live in the same house as them;
Non-participation in any social organization [
1,
6].
According to the results obtained from the analyses performed by Maltby et al. [
6], social isolation—as assessed in the English Longitudinal Study of Aging and in accordance with the elements suggested by Gale et al. [
1]—includes three dimensions:
a) ‘Nuclear family’—through the status of unmarried or non-cohabitant and isolation from children;
b) ‘Immediate family’—through isolation from parents and relatives;
c) ‘Extended social network’—isolation from friends and social organizations.
In addition, another finding described by Maltby et al. [
6] is that social isolation, compared to having an extensive social network, predicts the frailty index for a period of more than four years both for basic frailty and other variables (e.g., age, socio-economic status, educational abilities, depressive symptoms, smoking).
RISK FACTORS
The definition of frailty is mainly based on physical markers, such as low grip strength or a decrease in mobility and balance, without taking into account (most of the time) domains related to cognitive, mental, and social health, which can be reflected in loneliness and social isolation [
34,
35,
36].
Although there are factors (
Figure 1) that predispose older individuals to the development of frailty, including low socio-economic status, comorbidities, poor diet, and sedentary lifestyles, everyone in their latter part of life is at risk of becoming frail [
37]. Nevertheless, to the point where it becomes a pre-death phase, frailty is potentially preventable [
37], and there is a belief that it could even be reversed if there is an early screening process followed by appropriate interventions [
38].
Aging is a factor of physiological frailty, regardless of the level of physical activity [
2]. Elderly individuals become more vulnerable when they have concomitant chronic diseases, are exposed to acute infections, or are prone to falls [
2]. Studies have demonstrated that an increase in the C-reactive protein (CRP) level, fibrinogen, and overall inflammatory activity, as well as increased blood cortisol, are also risk factors for frailty [
19]. In addition to clinical, biological, and lifestyle factors, social criteria such as social isolation or loneliness [
37] should be included in screening programs for frailty [
19].
The bidirectional relationship between frailty and loneliness was assessed in a study [
13] that followed the transition of frailty in two cohorts after 2008, followed up in 2011 and 2014. Tendencies to remain in a frailty state were associated with increased levels of loneliness observed over a period of three years: compared to patients who never felt lonely, those who often felt lonely were less likely to remain in the robust or pre-frail state. Additionally, in the group following a worsening of health, loneliness was a risk factor, such that increased levels of loneliness were associated with increased frailty over time [
13].
According to Hanlon et al., social isolation and/or loneliness are risk factors for increased hospitalization at all levels of frailty [
3]; moreover, it seems that risk of loneliness is more pronounced in those with a robust or pre-frail status [
3,
13].
Having a conjugal life, living with a partner, and being sexually active are factors correlated with robustness. Older people involved in couple activities seem to have a high quality of life based on common concerns for well-being, maintaining their social role, sharing common interests, and spending time practicing physical activity or having a healthy lifestyle. Companionship, trust, affection, and complicity are expressed in a particular way by older adults and seem to play an essential role in maintaining psychosocial identity and preserving interest in everyday life [
39].
A possible problem for elderly couples is represented by the fact that, with advancing age comes the difficulty of managing age-specific conditions or comorbidities. Sometimes, it is necessary for one of the members of the couple to take on the role of caregiver of the life partner, which can represent a serious problem for elderly individuals, especially for those who live alone (either because they have no offspring, or because their offspring live at long distances). It seems that female caregivers, caregivers with cognitive deterioration, and individuals who need help in carrying out household activities are the most prone to rapid deterioration and require a lot of attention from relevant healthcare providers [
40].
4. Discussion
The aging process and the association of chronic diseases with advanced age are conditions that necessitate careful evaluation and investigation of the health status. The prevalence of many diseases is increased in older populations. Surviving longer with diseases can be a factor in reducing functionality, implicitly leading to limitation of the activities of the elderly who then become dependent on their family and social care.
Aging causes not only numerous changes in the body and the appearance of chronic diseases but also socio-economic changes that represent a challenge both for elderly individuals and for society. Maintaining an adequate physical and mental status allows a better quality of life, which can ensure the involvement of older adults in social, economic, and cultural life. These aspects also contribute not only to increasing the life span of the elderly but also to maintaining the satisfaction of being useful to oneself and to those around.
With the passing of years and the appearance of disability, elderly individuals will come to depend on their family and society. In addition to the socio-economic support, active frailty screening is essential for the early detection of changes specific to the frailty syndrome and to ensure prompt interventions.
In primary healthcare, the proactive identification of loneliness, especially for the elderly population, should be a priority and should be constantly carried out at every medical visit, regardless of the physical health status of the patient, in order to ensure optimal interventions at the right time [
3]. After assessing the patient's degree of frailty and loneliness and/or social isolation, the attending physician can offer patient-centered care, which could lead to more optimistic results and avoid worsening of his/her condition [
37].
The loss of autonomy in elderly individuals is associated with needs of a medical, social, and psycho-affective nature [
41], which must be evaluated according to the criteria for classification in degrees of dependence in different types of assessment grids for the elderly[
42,
43]. In Romania, the national grid for assessing the needs of the elderly was revised in 2023, ensuring the complete assessment of dependent elderly people (
https://www.mmuncii.ro/j33/images/Documente/MMPS/Rapoarte_si_studii_MMPS/DPSS/2022_Substantiation_Study_for_LTC_Strategy_2023-2030_EN.pdf). Thus, seniors can be provided with
social and medical services adapted to their individual needs. Society can support seniors who need assistance with personal care not only through ensuring access to professional care services but also by creating help centers where the elderly can benefit from the provision of basic needs ranging from accommodation, care, and feeding to psychological support, social interaction, occupational therapy, religious/spiritual services, or legal counseling [
22,
33,
44].
In addition to the involvement of social services, the roles of primary care providers and geriatric specialists are essential. Furthermore, with growing importance as the degree of disability increases, palliative care services are representative multi-disciplinary stakeholders in the healthcare context [
22,
41,
44] and are the most suitable to develop current and terminal medical care approaches, being
one of the few services that can offer a holistic approach to the patient and those close to them [
22,
44].
Social isolation and loneliness are risk factors for chronic diseases but can also be their consequence [
41]. There exists a two-way path between them, and social isolation and loneliness can also dissuade an individual to fight against disease and weakness, reducing the chances of effectiveness of therapeutic interventions and worsening their status. Approaching the palliative rehabilitation care model adapted to elderly people with chronic non-oncological conditions can represent an opportunity to maintain interest in involvement in daily activities, thus maintaining their motivation to live as actively as possible in the last part of their lives [
41].
The primary limitation of our study arises from the design of the included studies and their heterogeneity in terms of the evaluation of frailty and/or loneliness or social isolation. In this context, no final resolution can be postulated. Further studies are required to better understand the double pathway between frailty and loneliness in elderly individuals.