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International Journal of
Environmental Research
and Public Health
Systematic Review
Informal Caregiving, Loneliness and Social Isolation:
A Systematic Review
AndréHajek * , Benedikt Kretzler and Hans-Helmut König
Citation: Hajek, A.; Kretzler, B.;
König, H.-H. Informal Caregiving,
Loneliness and Social Isolation: A
Systematic Review. Int. J. Environ.
Res. Public Health 2021,18, 12101.
https://doi.org/10.3390/
ijerph182212101
Academic Editor: Paul B. Tchounwou
Received: 1 November 2021
Accepted: 17 November 2021
Published: 18 November 2021
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Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Hamburg Center for Health Economics, Department of Health Economics and Health Services Research,
University Medical Center, Hamburg-Eppendorf, 20246 Hamburg, Germany; b.kretzler.ext@uke.de (B.K.);
h.koenig@uke.de (H.-H.K.)
*Correspondence: a.hajek@uke.de
Abstract:
Background: Several empirical studies have shown an association between informal care-
giving for adults and loneliness or social isolation. Nevertheless, a systematic review is lacking
synthesizing studies which have investigated these aforementioned associations. Therefore, our
purpose was to give an overview of the existing evidence from observational studies. Materials and
Methods: Three electronic databases (Medline, PsycINFO, CINAHL) were searched in June 2021.
Observational studies investigating the association between informal caregiving for adults and
loneliness or social isolation were included. In contrast, studies examining grandchild care or private
care for chronically ill children were excluded. Data extractions covered study design, assessment of
informal caregiving, loneliness and social isolation, the characteristics of the sample, the analytical
approach and key findings. Study quality was assessed based on the NIH Quality Assessment Tool
for Observational Cohort and Cross-Sectional Studies. Each step (study selection, data extraction and
evaluation of study quality) was conducted by two reviewers. Results: In sum, twelve studies were
included in our review (seven cross-sectional studies and five longitudinal studies)—all included
studies were either from North America or Europe. The studies mainly showed an association
between providing informal care and higher loneliness levels. The overall study quality was fair to
good. Conclusion: Our systematic review mainly identified associations between providing informal
care and higher loneliness levels. This is of great importance in assisting informal caregivers in
avoiding loneliness, since it is associated with subsequent morbidity and mortality. Moreover, high
loneliness levels of informal caregivers may have adverse consequences for informal care recipients.
Keywords:
informal caregiving; loneliness; private caregiving; social exclusion; social isolation;
spousal caregiving
1. Introduction
Remaining in familiar environments is often important for individuals in late life [
1
,
2
].
Therefore, home care is often preferred [
3
,
4
]. As the number of individuals needing care is
likely to increase due to reasons of demographic ageing, home care is of great importance.
A key part of home care is the provision of informal care. This can be defined as
the provision of private care for relatives, friends or neighbors in frequent need of care,
including tasks such as personal care or simply assistance with the household [
5
]. A large
body of evidence exists clearly demonstrating an association between informal caregiving
and adverse health outcomes (such as decreased mental health, e.g., [6–8]).
Drawing on the caregiver stress model proposed by Pearlin et al. [
9
], informal care-
giving can include several stressors such as burden [
10
]. These stressors can contribute to
feelings of social isolation or loneliness [
11
]. Some studies have examined loneliness or
social isolation in informal caregivers (e.g., [
12
–
15
]), partly demonstrating a link between
provision of informal care and increased loneliness. This is plausible given the fact that
informal caregiving can reduce the time available for family and friends due to reasons
Int. J. Environ. Res. Public Health 2021,18, 12101. https://doi.org/10.3390/ijerph182212101 https://www.mdpi.com/journal/ijerph
Int. J. Environ. Res. Public Health 2021,18, 12101 2 of 12
of prioritizing [
16
]—which can result in loneliness or isolation. Nevertheless, informal
caregiving can also contribute to an increased size of social networks (e.g., by establishing
contacts with other informal caregivers) and may therefore reduce feelings of loneliness or
social isolation. Since a systematic review systematically synthesizing evidence regarding
the association between informal caregiving (provided for adults) and loneliness or social
isolation based on observational studies is lacking, our aim was to fill this gap in knowl-
edge. Knowledge about this association may help to reduce these factors—which in turn,
is of relevance since they are associated with several chronic illnesses, decreased perceived
life expectancy [17,18] and reduced actual longevity [19,20].
It should be noted that loneliness and social isolation are related but distinct con-
cepts [
21
]. For example, previous research showed a Pearson correlation of about five
between loneliness and perceived social isolation [
17
]. While loneliness refers to the feeling
that one’s social network is of a poorer quality or is smaller than desired [
22
,
23
], perceived
social isolation refers to the feeling that one does not belong to society [
22
,
23
]. They also
differ in their correlates and consequences (for further details, please see [
17
]). Both have
in common the fact that they refer to social needs [24].
2. Methods
The methodology of this review satisfied the Preferred Reporting Items for Systematic
Reviews and Meta-Analysis guidelines [
25
]. Additionally, this review is registered with
the International Prospective Register of Systematic Reviews (PROSPERO, registration
number: CRD42020193099). Moreover, a study protocol has been published [26].
2.1. Search Strategy and Selection Criteria
In June 2021, a systematic literature search was conducted in three databases (PubMed,
PsycINFO, and CINAHL). The search query for PubMed is described in Table 1. A two-
step process was used involving: 1. title/abstract screening and 2. full-text screening
(independently by two reviewers (AH and BK). Additionally, a hand search was performed.
Discussions were used when disagreements occurred. This approach was also used for
data extraction and assessment of study quality.
Table 1. Search strategy (Medline search algorithm).
# Search Term
#1 Informal Careg *
#2 Family careg *
#3 Private careg *
#4 Spousal careg *
#5 Parental careg *
#6 #1 OR #2 OR #3 OR #4 OR #5
#7 Lonel *
#8 Social isolation
#9 Social exclusion
#10 #7 OR #8 OR #9
#11 #6 AND #10
Table notes: The asterisk (*) is a truncation symbol. The number sign (#) refers to the search order.
Inclusion criteria were:
•
cross-sectional and longitudinal observational studies analyzing the association be-
tween informal caregiving for adults (i.e.,
≥
18 years) and loneliness or social isolation
•operationalization of main variables with established tools
•studies in English or German language
Int. J. Environ. Res. Public Health 2021,18, 12101 3 of 12
•published in a peer-reviewed, scientific journal
In contrast, exclusion criteria were:
•studies examining grandchild care (e.g., [27,28])
•studies examining private care for chronically ill children
•
studies exclusively using samples with a specific disorder among the caregivers (e.g.,
studies solely including caregivers with specific disorders)
•
Prior to the final eligibility criteria, a pre-test was conducted (with a sample of 100
title/abstracts). Nevertheless, it should be emphasized that our criteria remained
unchanged.
2.2. Data Extraction and Analysis
One reviewer (BK) carried out the data extraction, cross-checked by a second reviewer
(AH). The data extraction covered the design of the study, operationalization of key vari-
ables (informal caregiving and loneliness/social isolation), characteristics of the sample,
analytical approach, and important results.
2.3. Assessment of Study Quality/Risk of Bias
The study quality was assessed using the NIH Quality Assessment Tool for Observa-
tional Cohort and Cross-Sectional Studies [
29
]. It is a well-known and widely used tool
when dealing with observational studies (e.g., [30,31]).
3. Results
3.1. Overview of Included Studies
Figure 1displays the selection process. In sum, n= 12 studies were included in
our review [
11
,
14
,
32
–
41
]. The main findings are displayed in Table 2(if given, adjusted
results are shown in Table 2). Data came from North America (n= 5, all studies from the
United States), and Europe (n= 7 studies, with three studies from Germany, one study
from Norway, one study from Sweden, one study from the United Kingdom, and one
study using data from Austria, Belgium, the Czech Republic, Denmark, Estonia, France,
Germany, Italy, Luxembourg, Spain, and Switzerland). While seven studies were cross-
sectional [
32
–
35
,
37
,
40
,
41
], five studies had a longitudinal design [
11
,
14
,
36
,
38
,
39
]. Among
the longitudinal studies, the number of waves used ranged from two to four waves. The
period of observation ranged from three to twelve years.
Two studies only used versions of the De Jong Gierveld scale to quantify loneliness
and two studies only used different versions of the UCLA loneliness scale to quantify
loneliness. Moreover, one study used the Bude and Lantermann scale to quantify perceived
social isolation and the De Jong Gierveld scale to quantify loneliness. The other studies
used different tools or single item measures to quantify feelings of loneliness. Half of the
studies used a dichotomous variable to quantify the presence of informal caregiving. The
other studies examined spousal caregiving or distinguished between, for example, current
caregiving, former caregiving and non-caregiving.
Among the longitudinal studies, two studies used specific panel regression models
to exploit the longitudinal data structure and to reduce the challenge of unobserved
heterogeneity [
42
]. Based on these panel regression models, consistent estimates can be
derived [42].
The sample size ranged from 101 to 29,458 observations (in sum, 91,857 observations).
The studies mainly examined middle-aged and older individuals (average age ranged from
45.0 years to 83.7 years across the studies). The proportion of women in the samples mainly
ranged from about 50% to 60%, whereas two studies had about 70% of women. Further
details are shown in Table 2.
Int. J. Environ. Res. Public Health 2021,18, 12101 4 of 12
Int. J. Environ. Res. Public Health 2021, 18, x 4 of 13
Figure 1. Flow Chart.
Figure 1. Flow Chart.
Int. J. Environ. Res. Public Health 2021,18, 12101 5 of 12
Table 2. Study overview and important findings.
First Author Country Assessment of
Informal Care
Assessment of
Loneliness or Social
Isolation
Study Type Sample
Characteristics
Sample Size;
Age;
Females in Total Sample
Results
Beach (2021) [32] United States dichotomous
(yes/no)
increase in loneliness
due to COVID-19
(yes/no)
cross-sectional family caregivers and
non-caregivers
n= 3509;
M: 58.5, SD: 16.2; 18–100;
69.5%
Regarding a t-test, there were no
differences in the changes of
loneliness due to COVID-19 between
caregivers and non-caregivers.
Beeson (2003 [33]) United States dichotomous
(yes/no)
UCLA Loneliness Scale
(20 items) cross-sectional
Alzheimer’s disease
caregiving spouses
and non-caregiving
spouses
n= 101;
M: 75.8, SD: 8.4;
58.4%
According to a t-test, caregiving
spouses had significantly higher
loneliness levels than non-caregiving
spouses (37.4 vs. 33.1, p< 0.05).
Brandt (2021) [34] Germany
providing assistance
which is necessary for
others (yes/no)
missing company
(yes/no) cross-sectional
community-dwelling
individuals aged 40
years and older
n= 353;
M: 58.9, 40–91;
72.0%
According to logistic regression,
people who provided assistance
were significantly less likely to miss
company (ß = −0.17, p< 0.05).
Ekwall (2005) [35] Sweden dichotomous
(yes/no)
loneliness (three items
rated on
four-point-scale)
cross-sectional
population-based
sample consisting of
individuals aged 75
years and older
n= 4278;
M: 83.7, SD: 5.5;
60.6%
Feelings of loneliness were more
frequent among non-caregivers (e.g.,
recurrent feelings of loneliness:
10.9% vs. 5.8%, p< 0.001).
Gallagher (2020) [36]United
Kingdom
dichotomous
(yes/no)
loneliness during the
last three weeks rated
on a three-point scale
longitudinal
(two waves
from 2017 to
2020)
Understanding
Society/UK
Household
Longitudinal Study
n= 7537;
M: 48.4, SD: 17.2;
53.1%
Regarding F-tests, carers had
significantly higher levels of
loneliness before COVID-19 (8.0% vs
7.5%, p< 0.001) and during
COVID-19 (8.2% vs 7.1%, p< 0.05).
Hajek (2019) [14] Germany dichotomous
(yes/no)
De Jong Gierveld
Loneliness Scale (eleven
items)
longitudinal
(four waves
from 2002 to
2014)
German Ageing
Survey
n= 21,762;
M: 62.3, SD: 11.4, 40–95;
49.6%
According to fixed-effects regression,
there were no significant differences
in loneliness.
Hansen (2015) [37] Norway
non-caregiver;
in-household
caregiver;
out-of-household
caregiver
De Jong Gierveld
Loneliness Scale (eight
items)
cross-sectional
Norwegian Life
Course, Ageing and
Generation study
n= 11,047;
M: 45.0, SD: 11.0, 25–64;
51.2%
Regression analysis showed that
in-household caregivers (compared to
non-caregivers) have increased levels
of loneliness (ß = 0.13, p< 0.05). In
addition, the interactions
in-household caregiver x part-time
employment (ß = 0.27, p< 0.05) and
in-household caregiver x
non-working (ß = 0.20, p< 0.05) were
also related to increased loneliness.
Hawkley (2020) [38] United States spousal caregiver
(yes/no)
UCLA Loneliness Scale
(three items)
longitudinal
(two waves
from 2010 to
2015)
National Social Life,
Health and Aging
Project
n= 970;
≤64: 32.0%
65–74: 46.8%
75–84: 19.9%
≥85: 1.5%;
50.0%
t-tests revealed no significant
differences between caregivers and
non-caregivers.
Int. J. Environ. Res. Public Health 2021,18, 12101 6 of 12
Table 2. Cont.
First Author Country Assessment of
Informal Care
Assessment of
Loneliness or Social
Isolation
Study Type Sample
Characteristics
Sample Size;
Age;
Females in Total Sample
Results
Robinson-Whelen (2001)
[39]United States
current caregiver;
former caregiver;
non-caregiver
New York University
Loneliness Scale (three
items)
longitudinal
(four waves
during four
years)
caregivers and control
participants
n= 143;
M: 69.3, SD: 8.9
Female: not specified
Regarding the graphical
presentation, both former and
current caregivers had higher levels
of loneliness than a control group.
Robison (2009) (Robison
et al., 2009) [40]United States dichotomous
(yes/no) going out too little cross-sectional
Connecticut
Long-Term Care
Needs Assessment
n= 4041;
M: 71.5;
61.1%
Logistic regression did not reveal a
significant association between
caregiving and social isolation.
Wagner (2018) [41]
Austria,
Belgium, the
Czech Republic,
Denmark,
Estonia, France,
Germany, Italy,
Luxembourg,
Spain, and
Switzerland
spousal caregiver
(yes/no)
UCLA Loneliness Scale
(three items) cross-sectional
Survey of Health,
Ageing and
Retirement in Europe
n= 29,458;
M: 64.5
SD: 9.4
30–95;
50.4%
According to regression analysis,
spousal care was correlated with
increased levels of loneliness
(ß = 0.12, p< 0.001).
Zwar (2020) [11] Germany
not reporting care at
baseline but having
started to do so at
follow-up
loneliness: De Jong
Gierveld Loneliness
Scale (six items)social
isolation: instrument
from Bude and
Lantermann (2006)
(Bude and Lantermann,
2006) (four items)
longitudinal
(two waves
from 2014 to
2017)
German Ageing
Survey
n= 8658;
M: 65.9
SD: 10.6;
54.5%
Fixed-effects regression found
caregiving to be significantly
associated with higher levels of
loneliness among men (ß = 0.93,
p< 0.01
), but not with social isolation.
Int. J. Environ. Res. Public Health 2021,18, 12101 7 of 12
In the next sections, the results are displayed as follows: 1. Informal caregiving
and loneliness (cross-sectional studies, thereafter longitudinal studies), and 2. Informal
caregiving and social isolation (cross-sectional studies, thereafter longitudinal studies).
3.2. Informal Caregiving and Loneliness
In sum, n= 11 studies examined the association between informal caregiving and
loneliness (six cross-sectional studies and five longitudinal studies).
With regard to cross-sectional studies, four studies found an association between
caregiving and increased levels of loneliness [
33
,
35
,
37
,
41
], whereas one study found no
association between these factors [
32
]. Moreover, one study found an association be-
tween caregiving and a decreased likelihood of loneliness [
34
]. However, this study was
conducted during the COVID-19 pandemic.
With regard to longitudinal studies, three studies found an association between
caregiving and increased loneliness levels [
11
,
36
,
39
], whereas two studies did not identify
significant differences [
14
,
38
]. One of the three studies which found significant differences
only found these among men, but not women [11].
3.3. Informal Caregiving and Social Isolation
In sum, n= 2 studies examined the association between informal caregiving and
social isolation (one cross-sectional study and one longitudinal study). Both studies did
not find an association between these factors [
11
,
40
]. It should be noted that one of these
studies examined both the association between informal caregiving and loneliness as well
as between informal caregiving and social isolation [11].
3.4. Quality Assessment
The assessment of the study quality of the studies included in our review is displayed
in Table 3. While some important criteria were achieved by all studies (e.g., clear aim of the
study or valid assessments of important variables), a few other criteria were only partly
(e.g., adjustment for covariates) or hardly ever met (e.g., sufficient response rate or small
loss to follow-up). Nevertheless, the overall study quality was quite high (seven studies
were rated as ‘good’ and five studies were rated as ‘fair’; none of the studies were rated as
‘poor’).
Int. J. Environ. Res. Public Health 2021,18, 12101 8 of 12
Table 3. Quality Assessment.
Paper Author and Date
1. Was the Research Question
or Objective in This Paper
Clearly Stated?
2. Was the Study Population Clearly
Specified and Defined?
3. Was the Participation Rate of
Eligible Persons at Least 50%?
4. Were all the Subjects Selected or Recruited
from the Same or Similar Populations
(Including the Same Time Period)? Were
Inclusion and Exclusion Criteria for Being in
the Study Prespecified and Applied Uniformly
to All Participants?
5. Was a Sample Size Justification,
Power Description, or Varianceand
Effect Estimates Provided?
6. For the Analyses in This Paper, Were the
Exposure(s) of Interest Measured Prior to
the Outcome(s) Being Measured? (if not
Prospective Should Be Answered as ‘no’,
Even Is Exposure Predated Outcome)
7. Was the Timeframe Sufficient so
That One Could Reasonably Expect
to See an Association between
Exposure and Outcome if It Existed?
Beach (2021)) [32] Yes Yes No (40%) Yes No No (cross-sectional) No (cross-sectional)
Beeson (2003 [33]) Yes Yes Not reported Yes No No (cross-sectional) No (cross-sectional)
Brandt (2021) [34] Yes Yes Notreported Yes No No (cross-sectional) No (cross-sectional)
Ekwall (2005) [35] Yes Yes Yes (52.8%) Yes Yes No (cross-sectional) No (cross-sectional)
Gallagher (2020) [36] Yes Yes Not reported Yes No No (simultaneously) Yes
Hajek (2019) [14] Yes Yes No (e.g., 38% response rate in wave 2) Yes No No (simultaneously) Yes
Hansen (2015) [37] Yes Yes No (43.2%) Yes No No (cross-sectional) No (cross-sectional)
Hawkley (2020) [38] Yes Yes Yes (e.g., 87% in wave 2) Yes No No (simultaneously) Yes
Robinson-Whelen (2001)
[39]Yes Yes Not reported Yes No No (simultaneously) Yes
Robison (2009) (Robison
et al., 2009) [40]Yes Yes No (29%) Yes No No (cross-sectional) No (cross-sectional)
Wagner (2018) [41] Yes Yes Not reported Yes No No (cross-sectional) No (cross-sectional)
Zwar (2020) [11] Yes Yes No (e.g., 27.1% in wave 5) Yes No No (simultaneously) Yes
Paper Author and Date
8. For exposures that can vary
in amount or level, did the
study examine different levels
of the exposure as related to
the outcome (e.g., categories of
exposure, or exposure
measured as continuous
variable)?
9. Were the exposure measures
(independent variables) clearly
defined, valid, reliable, and
implemented consistently across all
study participants?
10. Was the exposure(s) assessed
more than once over time?
11. Were the outcome measures (dependent
variables) clearly defined, valid, reliable, and
implemented consistently across all study
participants?
12. Was loss to follow-up after
baseline 20% or less?
13. Were key potential confounding
variables measured and adjusted
statistically for their impact on the
relationship between exposure(s) and
outcome(s)?
Overall quality judgement
Beach (2021)) [32] Dichotomous Yes Not applicable Yes Not applicable No Good
Beeson (2003 [33]) Dichotomous Yes Not applicable Yes Not applicable No Fair
Brandt (2021) [34] Dichotomous Yes Not applicable Yes Not applicable Yes Fair
Ekwall (2005) [35] Dichotomous Yes Not applicable Yes Not applicable No Fair
Gallagher (2020) [36] Dichotomous Yes Yes Yes Not reported No Fair
Hajek (2019) [14] Dichotomous Yes Yes Yes Not reported Yes Good
Hansen (2015) [37] Three categories Yes Not applicable Yes Not applicable Yes Good
Hawkley (2020) [38] Dichotomous Yes Yes Yes Not reported Yes Good
Robinson-Whelen (2001)
[39]Three categories Yes Yes Yes Not reported No Fair
Robison (2009) (Robison
et al., 2009) [40]Dichotomous Yes Not applicable Yes Not applicable Yes Good
Wagner (2018) [41] Dichotomous Yes Not applicable Yes Not applicable Yes Good
Zwar (2020) [11] Dichotomous Yes Yes Yes No (e.g., follow-up rate from the
panel sample was 63% in wave 6) Yes Good
Int. J. Environ. Res. Public Health 2021,18, 12101 9 of 12
4. Discussion
4.1. Main Findings
In summary, twelve studies were included in our review (seven cross-sectional studies
and five longitudinal studies)—all included studies were either from North America or
Europe. The studies mainly showed an association between providing informal care and
higher loneliness levels. The overall study quality was fair to good. Such knowledge
about an association between informal caregiving and loneliness is of great importance
for targeting target individuals at risk of increased levels of loneliness, which in turn may
assist in maintaining health.
4.2. Possible Mechanisms
Rather unsurprisingly, most of the studies included found an association between the
provision of informal care and increased levels of loneliness. While only single studies
(e.g., [
43
]) identified positive health consequences of informal caregiving, most of the
studies showed harmful consequences of private care (e.g., on sleep [
44
], mental health
or life satisfaction [
7
,
8
,
44
,
45
]). These harmful consequences may contribute to feelings of
loneliness. More precisely, specific depressive symptoms such as anhedonia (inability to
experience pleasure) may reduce motivation to perform social activities [
46
]. This in turn
may result in feelings of loneliness. Furthermore, the reduced sleep quality caused by
performing informal care may also inhibit physical and cognitive activities [
44
] which can
ultimately contribute to reduced loneliness scores. Similarly, a reduced satisfaction with
life can directly contribute to social withdrawal or feeling lonely [47].
Furthermore, the association between informal caregiving and increased loneliness
may be explained by the fact that informal caregiving limits social contacts [
48
–
50
]. In turn,
this may enhance emotions of loneliness caused by the restricted leisure time for social
activities [51], caregiving burden or emotions such as guilt or resentment [48–50].
4.3. Comparability of Studies
Several factors limit the comparability of the studies included. For example, both
loneliness and social isolation were quantified using different tools. None of the studies
examined the association between informal caregiving and objective social isolation. Infor-
mal caregiving was also assessed differently between the studies. More than half of the
studies included used cross-sectional data. Out of the five longitudinal studies, only two
used specific panel regression models. Such models are required to produce consistent
estimates [
42
]. With regard to cultural differences, the included studies exclusively referred
to data from North America or Europe.
4.4. Gaps in Knowledge and Guidance for Future Research
Our current systematic review determined various gaps in our current knowledge.
First, more longitudinal studies are needed to identify the impact of caregiving on loneliness
and social isolation. Second, more studies using data from nationally representative
samples are desirable. Third, caregiving types could be taken into consideration in future
studies (e.g., from pure supervision to performing nursing care services [
43
,
52
]). Fourth,
the relationship between caregiver and care-recipient (e.g., spousal caregiving vs. parental
caregiving or inside household caregiving vs. outside household caregiving) should be
taken into consideration. Fifth, the care-recipients should be clearly characterized (e.g.,
care recipient with cancer vs. care recipient with dementia)—if data are available. Sixth,
future research should ideally use established instruments such as the De Jong Gierveld
scale or the UCLA loneliness scale. Seventh, many more studies should also consider
the impact of caregiving on (perceived and objective) social isolation. Eighth, research
from other areas of the world (other than Europe and North America) is urgently needed.
Ninth, the underlying mechanisms in the association between caregiving and loneliness
as well as social isolation should be explored. Tenth, the association between caregiving
Int. J. Environ. Res. Public Health 2021,18, 12101 10 of 12
and loneliness/social isolation should be further explored during (or after) the COVID-19
pandemic. Eleventh, subgroup analyses (e.g., stratified by gender) are desirable.
4.5. Strengths and Limitations
This is the first systematic review regarding the association between informal caregiv-
ing and loneliness/social isolation. The important steps were conducted by two reviewers.
A meta-analysis was not performed due to study heterogeneity. Since we restricted our
search to articles published in peer-reviewed articles, some important studies may be
excluded from this review. However, it should be noted that a certain quality of the studies
is ensured by this inclusion criterion.
5. Conclusions
In conclusion, our systematic review mainly identified associations between providing
informal care and higher loneliness levels. This is of great importance in assisting informal
caregivers in avoiding loneliness, since it is associated with subsequent morbidity and
mortality. Moreover, high loneliness levels of informal caregivers may have adverse conse-
quences for informal care recipients (e.g., in terms of earlier admission to nursing homes or
decreased informal care quality). Thus, avoiding higher loneliness levels of individuals
providing informal care may, more generally, assist in improving the relationship between
informal caregivers and informal care recipients—which could be examined in future
studies. This may also contribute to successful ageing in both informal caregivers and
care recipients.
Author Contributions:
The study concept was developed by A.H., B.K. and H.-H.K. The manuscript
was drafted by A.H. and critically revised by B.K. and H.-H.K. The search strategy was developed by
A.H. and H.-H.K. Study selection, data extraction, and quality assessment were performed by A.H.
and B.K., with H.-H.K. as a third party in case of disagreements. A.H., B.K. and H.-H.K. contributed
to the interpretation of the extracted data and writing of the manuscript. All authors have read and
agreed to the published version of the manuscript.
Funding:
This research did not receive any specific grants from funding agencies in the public,
commercial, or not-for-profit sectors.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
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