Introduction
The progressive aging of the global population, triggered by low fertility rates and longer life expectancy, is a global issue that requires research and policies to address the growing needs of the elderly.
Old-age loneliness has been of global concern for decades, but with the outbreak of COVID-19, and the consecutive pandemic measures applied the world over, such as lockdown and social distancing, it has shifted to become a primary concern to care-providing organizations and policymakers (Patel and Clark-Ginsberg, Reference Patel and Clark-Ginsberg2020). Stay-at-home orders may have affected social connectedness of the elderly and increased their loneliness, especially of those already living alone (Armitage and Nellums, Reference Armitage and Nellums2020). Concerns about the psychological well-being of elders who live alone and the devastating consequences of loneliness are receiving growing attention worldwide.
Loneliness becomes highly prevalent with age. Surveys in Europe and the USA estimated that the prevalence of loneliness ranges from 5% to 43% in the elderly (Djernes, Reference Djernes2006; Dykstra, Reference Dykstra2009; Pinquart and Sörensen, Reference Pinquart and Sörensen2000), making it an important issue. The causes may range from personal to societal factors. Since various critical events (e.g. loss of a spouse, admission to a nursing home, and loss of functional abilities) tend to occur later in life, loneliness is frequent in old age and has been shown to be an increasing challenge (Tesch-Roemer & Huxhold, Reference Tesch-Roemer, Huxhold and Knight2019). For the elderly, loneliness is often associated with mental health problems (Luanaigh and Lawlor, Reference Luanaigh and Lawlor2008), cognitive decline (Martin et al., Reference Martin, Hagberg and Poon1997; Shankar et al., Reference Shankar, Hamer, McMunn and Steptoe2013), poor self-rated health (Nummela et al., Reference Nummela, Seppänen and Uutela2011), and increased mortality (Holt-Lunstad et al., Reference Holt-Lunstad, Smith, Baker, Harris and Stephenson2015; Tilvis et al., Reference Tilvis, Laitala, Routasalo and Pitkälä2011). Being alone or living alone does not always imply the negative experience of loneliness. Although it may increase the risk of loneliness, not all elderly people who live alone feel lonely and vice versa. Being alone and loneliness are two well-distinguished concepts. Living alone becomes detrimental when it leads to loneliness. De Jong-Gierveld (Reference De Jong-Gierveld1998) defined loneliness as “a situation in which the number of existing relationships is smaller than is considered desirable, as well as situations where the intimacy one wishes for has not been realized.” A distinction must be made with social isolation, which refers to the more objective absence of social contacts (Routasalo et al., Reference Routasalo, Savikko, Tilvis, Strandberg and Pitkälä2006). It is important to note that there is no direct association between network size and loneliness. People with a small network may be socially isolated without experiencing feelings of loneliness (Townsend and Tunstall, Reference Townsend, Tunstall and Townsend1973; Wenger et al., Reference Wenger, Davies, Shahtahmasebi and Scott1996). Weiss (Reference Weiss1973) distinguished two subtypes of loneliness: emotional and social. The former is related to the absence of one or more intimate figures, whereas the latter refers to the absence of a broader social network. Emotional loneliness refers to the absence of intimate relationships, whereas social loneliness has been defined as the absence of engaging social networks (De Jong-Gierveld and Kamphuis, Reference De Jong-Gierveld and Kamphuls1985). The loss of a relation can be a significant trigger for emotional loneliness (Tiilikainen and Seppanen, Reference Tiilikainen and Seppänen2017). Emotional loneliness may reveal itself to be particularly relevant when studying the elderly, as they are more likely to suffer bereavement. Older adults frequently report loneliness, which in turn has been proven to have a profoundly negative effect on depression (Cacioppe et al., Reference Cacioppo, Hughes, Waite, Hawkley and Thisted2006). In a systematic review, the authors found that loneliness is detrimental not only to health, but it is also an independent risk factor for depression (O’luanaigh et al., Reference O’luanaigh2012).
Late-life depression is a complex and heterogeneous disorder that has been associated with a chronic course (Haigh et al., Reference Haigh, Bogucki, Sigmon and Blazer2018), a higher risk of subsequent development of cognitive impairment or dementia (Singh-Manoux et al., Reference Singh-Manoux2017), and premature death (Blazer, Reference Blazer2003). Depression is one of the most common causes of disability, reducing life satisfaction in older people (Skoog, Reference Skoog2011). Old age seems to be significantly associated with a worse major depressive disorder. Studies estimate that from 3 to 16% of people may experience a depressive disorder in late life (Whiteford, Reference Whiteford2013) and up to 10% may experience an unremitting and chronic course of depressive symptoms (de la Torre-Luque et al., Reference de la Torre-Luque, de la Fuente, Prina, Sanchez-Niubo, Haro and Ayuso-Mateos2019). Prevalence of recurrent depression, characterized by a relapse in depression symptoms after a euthymic period, has been estimated to be between 25% and 40% (Richards, Reference Richards2011). These results underscore the need to identify which factors in the elderly have an impact on the recurrence of depressive symptoms. A systematic review found that the older population showed remission rates and response to treatment similar to those of middle-aged people, but relapse rates seemed higher in older age (Mitchell and Subramaniam, Reference Mitchell and Subramaniam2005). Another study reported how nearly half of depressed elders maintained their diagnosis even after 2 years, and that 61% had a chronic course of depressive symptoms (Comijs et al., Reference Comijs2015). The recurrence, relapse, and chronicity of late-life depression are well-known problems in daily practice. A longitudinal study found that the average symptom severity of depressed elders remained above the 85th percentile of the population average for 6 years. Symptoms were short-lived in only 14% of patients. Twenty-three percent reported remissions, 44% an unfavorable, yet fluctuating course, and 32% maintained severe, chronic symptoms (Beekman et al., Reference Beekman2002). Poor recovery from the depressive disorder has been shown to be related to low perceived social support (Leskelä et al., Reference Leskelä2006; Nasser and Overholser, Reference Nasser and Overholser2005). Another cross-sectional study (Houtjes et al., Reference Houtjes, Van Meijel, Deeg and Beekman2010) demonstrated that depression severity is associated with several unmet social needs of older patients.
Although major depressive episodes are less common in older age (1–4%), what is referred to as subclinical depression is a particularly relevant phenomenon (8–16%) (Alexopoulos, Reference Alexopoulos2005; Blazer, Reference Blazer2003). Subsyndromal symptomatic depression or subthreshold depression (SSD) is defined as the presence of depressive symptomatology that does not meet the diagnostic criteria for a major depressive disorder (Meeks et al., Reference Meeks, Vahia, Lavretsky, Kulkarni and Jeste2011). Though SSD is not recognized as a formal disorder by the Diagnostic and Statistical Manual of Mental Disorders, it has been associated with multiple comorbidities including psychiatric and cognitive disorders, decreased functioning and quality of life, mortality, and financial costs to society (Kasckow et al., Reference Kasckow2013; Laborde-Lahoz et al., Reference Laborde-Lahoz, El-Gabalawy, Kinley, Kirwin, Sareen and Pietrzak2015; Lyness et al., Reference Lyness, King, Cox, Yoediono and Caine1999).
Previous research suggests that loneliness and depression are associated and often co-occur. Evidence on the association of aging with loneliness and depressive symptoms is contradictory, and there is a lack of longitudinal research in the elder population group. Loneliness may be either a risk factor for depression (Blazer, Reference Blazer2002; Heikkinen and Kauppinen, Reference Heikkinen and Kauppinen2004) or a consequence of mental health problems (Bowling et al., Reference Bowling, Edelmann, Leaver and Hoekel1989). Some studies suggest a bidirectional association between loneliness and depression (Hsueh et al., Reference Hsueh, Chen, Hsiao and Lin2019; Tiikkainen and Heikkinen, Reference Tiikkainen and Heikkinen2005), and others consider depression to be the independent variable, and loneliness as the outcome variable (Dahlberg et al., Reference Dahlberg, Andersson, McKee and Lennartsson2015; Emerson and Jayawardhana, Reference Emerson and Jayawardhana2016). We decided to select original research that measured the impact of loneliness on depression in the elderly. Most of the evidence concerning the association between depression and loneliness is based on cross-sectional design studies. Little is known about the temporal association between loneliness and depression (Courtin and Knapp, Reference Courtin and Knapp2017). To fill the research gaps and to strengthen our knowledge on the impact of loneliness on depression over time, we included only longitudinal studies in this systematic review. We hypothesized that loneliness has an important impact on the new onset of an episode of depressive symptoms and the course of depression.
Methods
This research was conducted following the Preferred Reported Items for Systematic reviews and Meta-Analysis (PRISMA-P) guidelines (Moher et al., Reference Moher2015). For the purpose of this review, we chose to focus on longitudinal studies in order to investigate the relationship between loneliness (i.e. perceived social isolation or subjective loneliness) and depression in the elderly, more specifically the impact of loneliness on depression in healthy community-dwelling elders over 60 years of age. The search was carried out in July 2020. Several steps were taken in order to select the studies and extract the information (see Figure 1). The databases included were Scopus, PsycInfo, and PubMed. No restrictions on the date of publication or location of the studies were imposed. The keywords and their combination were defined prior to the search. We used a combination of search terms related to our population group of interest, social isolation and loneliness, and depression as a mental health outcome. Predefined keywords included “loneliness AND depress* AND elderly,” “loneliness AND depress* AND older,” “loneliness AND depress* AND aged,” “social isolation AND depress* AND elderly,” “social isolation AND depress* AND older,” and “social isolation AND depress* AND aged.” We searched for the keywords: in title, abstract and keywords in Scopus; in title and abstract in PubMed and abstract in PsycInfo. The combined search yielded 11,081 references. Duplicate records were identified through the electronic search and were removed using the reference manager software package Zotero.
Fig 1. PRISMA flow diagram showing the process used in the review.
Study eligibility criteria
After duplicates were removed, all titles and abstracts of the remaining studies were screened to select potentially relevant articles. Initially, we included original research in peer-reviewed articles, written in English, French, Dutch, German, and Italian that provided quantitative data on loneliness and depression. We excluded books, comments, conference papers, editorials, letters, and theses. To meet inclusion criteria, studies had to investigate both loneliness and depression in healthy community-dwelling elders over 60 years of age. Because we were interested in the impact of loneliness on depression, we excluded all articles that considered cognitive impairment as a mental health outcome. We excluded all intervention programs on loneliness and depression.
Subsequently, we decided to select only studies with a focused longitudinal design. Previously, we had excluded “longitudinal” as a search term to avoid the possibility of omitting any articles that, while being longitudinal in design, did not mention the term in the title or abstract.
For the final selection, we had three independent researchers review the full texts of all potentially eligible publications, to be coded as either included or excluded. We included all longitudinal designs that yielded a statistical estimate of the effect of loneliness on depression. Specifically, loneliness has to be measured at baseline and depression at follow-up. We contacted the authors to receive some missing data. In the end, 10 articles were included in this systematic review.
Coding strategy
Two coders independently distinguished the categories for the research design found in the articles. We used two categories to classify the relevant variables: 1) the longitudinal association between loneliness and depressive symptoms (Outcome 1) and 2) the clinical course of depressive symptoms (Outcome 2). The first category included all the results which relate the first measure of loneliness at the beginning of the research and the measure of depressive symptoms at the follow-up to the study. The second category contains all the results that related the clinical course of depressive symptoms (e.g. new onset, remission, and maintenance) during the study, and the measure of loneliness at the beginning of the research. The summary of main findings, the measures used by the studies, and the design of the analyses are reported in Table 1. The association was analyzed using the odds ratios (ORs), bivariate correlation, and β scores. The magnitude of the OR in the present review is discussed on the base of the classification proposed by Chen and colleagues in 2010, which reported as small an OR < 1.5, as medium an OR between 1.5 and 4.9, and as large an OR ≥ 5.0.
Table 1. Analyzed variables and main findings of the included studies
Effect size for OR: small* < 1.5; medium** 1.5–4.9; large*** ≥5.0.
Results
The articles included in the review were published between 1992 and 2019, six of which in the last 5 years. Six studies have been conducted in European countries, one study in the UK, one study in the USA, one in Taiwan, and one in Singapore (see Table 2). The overall sample was of over 1000 participants in 7 of the studies. One study relied on a subsample of a harmonized dataset using the results of six longitudinal studies (de la Torre-Luque et al., Reference de la Torre-Luque2019). The mean age of participants at the end of the research period was ≥75 in four studies and ≤75 in six studies. Five studies investigated the longitudinal association between loneliness and depressive symptoms (Outcome 1), while two studies concentrated exclusively on the clinical course of depressive symptoms in elderly people (Outcome 2). Three of them reported both clinical course and data on the impact of loneliness on depression over a number of years (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019; de la Torre-Luque et al., Reference de la Torre-Luque2019; Holvast et al., Reference Holvast, Burger, de Waal, van Marwijk, Comijs and Verhaak2015). The studies have taken into consideration covariates such as marital status (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019; de la Torre-Luque et al., Reference de la Torre-Luque2019; Green et al., Reference Green1992; Holvast et al., Reference Holvast, Burger, de Waal, van Marwijk, Comijs and Verhaak2015; Segel-Karpas et al., Reference Segel-Karpas, Ayalon and Lachman2018), social network (Green et al., Reference Green1992; Holvast et al., Reference Holvast, Burger, de Waal, van Marwijk, Comijs and Verhaak2015; Jeuring et al., Reference Jeuring2018; Lim and Kua, Reference Lim and Kua2011; Segel-Karpas et al., Reference Segel-Karpas, Ayalon and Lachman2018; Sjöberg et al., Reference Sjöberg, Östling, Falk, Sundh, Waern and Skoog2013; Steunenberg et al., Reference Steunenberg, Beekman, Deeg and Kerkhof2010), activities of daily living (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019; de la Torre-Luque et al., Reference de la Torre-Luque2019; Lim and Kua, Reference Lim and Kua2011; Segel-Karpas et al., Reference Segel-Karpas, Ayalon and Lachman2018); chronic physical diseases (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019; Holvast et al., Reference Holvast, Burger, de Waal, van Marwijk, Comijs and Verhaak2015; Hsueh et al., Reference Hsueh, Chen, Hsiao and Lin2019; Jeuring et al., Reference Jeuring2018; Steunenberg et al., Reference Steunenberg, Beekman, Deeg and Kerkhof2010), quality of life (Green et al., Reference Green1992, Hsueh et al., Reference Hsueh, Chen, Hsiao and Lin2019, Lim and Kua, Reference Lim and Kua2011), and age of retirement (Segel-Karpas et al., Reference Segel-Karpas, Ayalon and Lachman2018). Four studies had a follow-up period of 2 years, all of them used the pre- and post-test. Three studies had a follow-up period of 3, 5, and 6 years, all three used the pre- and post-test. Another study had a follow-up length of 6 years (three waves, every 3 years), and the longest longitudinal study had a follow-up period of 14 years (five waves, every 3–4 years). The study that relied on a subsample of a harmonized dataset used the results of six longitudinal studies. The overall follow-up period dated from 1995 to 2013. One study had a follow-up length of 4 years (three waves), another 6 years (four waves), another one 9 years (four waves), and three studies had a length of 11 years (3, 6, and 6 waves).
Table 2. Characteristics of the included studies
All studies used validated scales, such as the Center for Epidemiologic Studies Depression Scale (CES-D) (Radloff, Reference Radloff1977), the Geriatric Mental Scale (GMS) (Copeland et al., Reference Copeland, Kelleher, Kellet, Gourlay, Gurland, Fleiss and Sharpe1976), the Comprehensive Psychopathological Rating Scale (CPRS) (Arfwidsson et al., Reference Arfwidsson, Arn, Beskow, Ottosson and Persson1971; Åsberg et al., Reference Åsberg, Montgomery, Perris, Schalling and Sedvall1978), the Inventory of Depressive Symptoms Self-Report (IDS) (Rush et al., Reference Rush, Gullion, Basco, Jarrett and Trivedi1996), the Composite International Diagnostic Interview (CIDI) (Wittchen et al., Reference Wittchen, Robins, Cottler, Sartorius, Burke and Regier1991), the Geriatric Depression Scale (GDS) (Sheikh and Yesavage, Reference Sheikh and Yesavage1986), and the EURO-D (Guerra et al., Reference Guerra, Ferri, Llibre, Prina and Prince2015) to measure depressive symptoms. Loneliness was measured using both validated scales present in literature and tailored items. Validated scales utilized included the UCLA Loneliness Scale (University of California, Los Angeles) (Russell et al., Reference Russell, Peplau and Cutrona1980), the Rasch-Type Loneliness Scale (RTLS) (De Jong-Gierveld and Kamphuls, Reference De Jong-Gierveld and Kamphuls1985), and the Short Loneliness Scale of Hughes and colleagues (Hughes et al., Reference Hughes, Waite, Hawkley and Cacioppo2004), while five others utilized a single question tailored item regarding the subjective feeling of loneliness (e.g. Do you feel lonely?). Seven studies report on the association between loneliness and depression using the OR, one uses the β scores, another utilized Pearson’s correlation, and yet another study reported both OR and β scores.
As a result, we separated the main findings of the studies into Outcome 1 and 2 (see Table 1 for main findings).
Outcome 1 – the longitudinal association between loneliness and depressive symptoms
In this category, we included eight studies that investigated the temporal association between loneliness and depressive symptoms. All articles included in this category confirmed a positive and significant association between loneliness at baseline and depression at follow-up. Five studies reported the OR in their analysis. Two articles found a small but significant association (r = 0.16, p < 0.001; OR= 1.39, p = 0.003) (Hsueh et al., Reference Hsueh, Chen, Hsiao and Lin2019; Lim and Kua, Reference Lim and Kua2011). Three articles found a medium effect size (OR = 1.63; OR =1.82; OR = 3.81, p < 0.05) (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019; Green et al., Reference Green1992; Sjöberg et al., Reference Sjöberg, Östling, Falk, Sundh, Waern and Skoog2013) and one article found a large effect size (OR = 17.76, p < 0.001) (de la Torre-Luque et al., Reference de la Torre-Luque, de la Fuente, Prina, Sanchez-Niubo, Haro and Ayuso-Mateos2019). Two studies that used the β score suggest that loneliness is a significant determinant of depressive symptoms (β = 0.38, p < .001; β = 0.73, p < 0.001) (Holvast et al., Reference Holvast, Burger, de Waal, van Marwijk, Comijs and Verhaak2015; Segel-Karpas et al., Reference Segel-Karpas, Ayalon and Lachman2018).
Outcome 2 – the clinical course of depressive symptoms
An unfavorable course of depression was associated with loneliness at baseline. In one study (Holvast et al., Reference Holvast, Burger, de Waal, van Marwijk, Comijs and Verhaak2015), the findings suggested that acute levels of loneliness result in a slimmer chance of achieving remission from a depressive state. The effect size between very severe levels of loneliness and depressive symptoms is higher (OR = 0.96, p < 0.001) compared to severe (OR = 0.56, p = 0.22) and moderate (OR = 0.41, p = 0.03) loneliness levels.
At follow-up, two studies (Jeuring et al., Reference Jeuring2018; Steunenberg et al., Reference Steunenberg, Beekman, Deeg and Kerkhof2010) analyzed the absence or presence of a depression diagnosis in the elderly subjects who had been diagnosed with depression at baseline. Although the effect size was small, both studies found that loneliness was a significant predictor of recurrence of depression (OR = 1.26; OR= 1.1) at the end of the observation period.
Similarly, one study analyzed the effect of, from not feeling lonely at baseline, to remission of depression at follow-up (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019). Findings suggested a small association (OR = 1.39) between not feeling lonely and the recurrence of depression. Namely, those who felt less lonely had a higher probability of not feeling depressed at follow-up, compared to those who experienced a persistent condition of depression at the end of the study.
Two studies focused on the association between loneliness at baseline and persistence of depression at follow-up, by comparing depressed and non-depressed patients (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019; de la Torre-Luque et al., Reference de la Torre-Luque, de la Fuente, Prina, Sanchez-Niubo, Haro and Ayuso-Mateos2019). Research findings show that those who were still depressed at follow-up differed from those who had never been depressed, as they had experienced higher levels of loneliness. Both articles reported a medium effect size (OR = 3.10; OR = 5.929).
Discussion
This study aimed to offer a literature review about the longitudinal effect of loneliness on depressive symptoms in older adults. In agreement with previous literature, we conclude that loneliness was by far a strong stressor on depressive symptoms. All analyses revealed an association between loneliness and other depressive symptoms, or an even more unfavorable course of depression.
Overall, we can discuss the main findings of the current review from three different perspectives.
Firstly, loneliness appears to represent a risk factor for the development of depressive symptoms in old age. All the studies included in the review that investigated the temporal association between the two variables (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019; de la Torre-Luque et al., Reference de la Torre-Luque, de la Fuente, Prina, Sanchez-Niubo, Haro and Ayuso-Mateos2019; Green et al., Reference Green1992; Holvast et al., Reference Holvast, Burger, de Waal, van Marwijk, Comijs and Verhaak2015; Hsueh et al., Reference Hsueh, Chen, Hsiao and Lin2019; Lim and Kua, Reference Lim and Kua2011; Segel-Karpas et al., Reference Segel-Karpas, Ayalon and Lachman2018; Sjöberg et al., Reference Sjöberg, Östling, Falk, Sundh, Waern and Skoog2013) found that loneliness is a predictor of depression, as it facilitates the occurrence of depressive symptoms. Secondly, following the studies' results that focused on the clinical course of depression and its longitudinal association with loneliness (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019; de la Torre-Luque et al., Reference de la Torre-Luque2019; Holvast et al., Reference Holvast, Burger, de Waal, van Marwijk, Comijs and Verhaak2015; Jeuring et al., Reference Jeuring2018; Steunenberg et al., Reference Steunenberg, Beekman, Deeg and Kerkhof2010), we can affirm that loneliness plays a role in worsening depression. Those who had experienced more loneliness had a higher probability of showing an increase in depressive symptoms. Finally, the longitudinal effect of loneliness also appears to hinder remission from depression in the elderly. In fact, people who reported feeling lonely were more likely to maintain feelings of depression throughout the study.
All studies clarify the temporal order of loneliness and depression. However, causality association between loneliness and depression has to be investigated further. Indeed, an up-to-date bidirectional relationship has been found in several studies (Hsueh et al., Reference Hsueh, Chen, Hsiao and Lin2019; Tiikkainen and Heikkinen, Reference Tiikkainen and Heikkinen2005). This systematic review identifies loneliness as an important factor that has an impact on depressive symptoms in old age. Nevertheless, among the results of the included studies, we can observe a heterogeneity regarding the effect size outcome. This heterogeneity could be due to covariates included in the analysis of the research. Indeed, almost all the studies have implemented multivariate analyses in their research design. The observed heterogeneity in effect size may have been caused by various covariates analyzed and their impact on depressive symptoms.
Age-related conditions, such as cognitive impairment, impaired physical mobility, impairment in activities of daily living (ADL), financial difficulties, bereavement, living conditions, and personality traits such as lack of mastery and neuroticism, can cause difficulties in the maintenance of relationships and may act as potential covariates that moderate the association between loneliness and depression. Previous studies indicated age and female gender as important variables, but because of the small sample of articles retrieved, we could not further investigate age and gender differences. Although living alone and loneliness are well-distinguished concepts, a higher number of depressive symptoms have been found in those living alone rather than in those living with others (Lim and Kua, Reference Lim and Kua2011). Living in a collectivist or individualist culture can certainly moderate the effect of loneliness on depression, but the final sample of this systematic review is too small to suggest any conclusions. One study highlights the importance of cultural and socioeconomic aspects (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019). According to this study, different welfare programs can play a significant role. They indicate the need for countries, especially in Eastern and Southern Europe, to provide greater support, resources, and social benefits to the elderly (Conde-Sala et al., Reference Conde-Sala, Garre-Olmo, Calvó-Perxas, Turró-Garriga and Vilalta-Franch2019). As one study (Segel-Karpas et al., Reference Segel-Karpas, Ayalon and Lachman2018) demonstrated, employment provides social engagement and social support and acts as a protective factor that moderates the negative effect of loneliness on depressive symptoms. Future research should aim to provide interventions that enhance social engagement in the lives of the elderly. Lifestyle, daily routine, and social environment change a lot during the transition into retirement and could have a negative effect on both loneliness and depression.
From the present literature review, there is a lack of research results regarding moderators that can influence the association of loneliness and depressive symptoms, both in negative and positive ways. There is an urgent need to study all factors that could decrease the detrimental influence of loneliness on depression in the elderly.
Moreover, some limits that have been found in the included studies may have been caused by the mortality rate of the sample and the measures used to detect loneliness. In longitudinal studies with the elderly, numerous studies have to face a high rate of missing participants in following waves due to cognitive impairment and mortality. One study had attrition that was almost twice as high in the depressed group than in the non-depressed group: nearly 47% of the depressed elderly were lost due to mortality (Jeuring et al., Reference Jeuring2018). This result confirms previous results that depression is an important risk factor for mortality. This high loss of participants by the end of the study could have affected the association between the variables in the studies. Some studies measured loneliness via a single item (de la Torre-Luque et al., Reference de la Torre-Luque2019; Hsueh et al., Reference Hsueh, Chen, Hsiao and Lin2019; Sjöberg et al., Reference Sjöberg, Östling, Falk, Sundh, Waern and Skoog2013) which probably is not sensitive enough to consider the loneliness in elders and may have led to underreporting of loneliness. The research included in our review focuses on community-dwelling elderly people. This possible source of bias raises questions about extremely lonely people who may have been less motivated to participate or more difficult to recruit.
Loneliness does increase with age, not because of age, but because of the increasing of mental and physical disability and the decreasing of social integration (Jylhä, Reference Jylhä2004). Not much is known about the relationship between loneliness and depression, and even less research has been found on variables that could moderate this association. Most of the articles included in the present review consider only subjective feelings of loneliness, measured by validated scales or tailored items, omitting more objective measures. Objective and subjective loneliness are related, although this association is relatively modest (Hughes et al., Reference Hughes, Waite, Hawkley and Cacioppo2004). Future studies could investigate the relation between depression and both subjective loneliness and social isolation, or how loneliness moderates the relationship between social isolation and depression. Loneliness is not an irreversible aspect of getting old, so evidence-based interventions should be developed to prevent and treat the detrimental impact of loneliness on depression, development of dementia, and risk of mortality in the elderly. Nowadays, older adults have more access to a larger external social reserve, due to technological developments (Sjöberg et al., Reference Sjöberg, Östling, Falk, Sundh, Waern and Skoog2013). Technological solutions and low-tech interventions can be used to mitigate feelings of loneliness. The provision of equipment and training to both caregivers and the elderly could improve the disparity in access to, and knowledge of, digital resources. Implementation of interventions using new technological means could tackle the devastating effects of loneliness, promote participation and social network enrichment, enhance life satisfaction, and improve the overall well-being and quality of life of lonely elders.
As proven by literature, loneliness has detrimental effects on both physical and mental health, and COVID-19 measures may even have increased the dangerous consequences in this already vulnerable group of elders (Webb, Reference Webb2020). As a consequence, the need to develop and implement evidence-based interventions is more urgent than ever.
Conflict of interest
None.
Description of authors’ roles
B.A.L. Van As performed the research of the articles, reviewed titles and abstracts, analyzed and interpretated the results, and wrote the paper. E. Imbimbo analyzed and interpretated the results and wrote the paper. A. Franceschi performed the research of the articles and reviewed titles and abstracts. E. Menesini did the critical revision of the article and gave final approval of the article. A. Nocentini envisaged the problem, coordinated the research, did the critical revision of the article, and gave final approval of the article. All the authors revised the manuscript.
Open access
