The impact of social isolation and loneliness on cardiovascular disease risk factors: a systematic review, meta-analysis, and bibliometric investigation

Data on the association between social isolation, loneliness, and risk of incident coronary heart disease (CVD) are conflicting. The objective of this study is to determine the relationship between social isolation and loneliness, and the risk of developing cardiovascular disease (CVD) in middle age and elderly using meta-analysis. The purpose of the bibliometric analysis is to systematically evaluate the existing literature on the relationship between social isolation, loneliness, and the risk of developing cardiovascular disease (CVD) in middle-aged and elderly individuals. A comprehensive search through four electronic databases (MEDLINE, Google Scholar, Scopus, and Web of Science) was conducted for published articles that determined the association between social isolation and/or loneliness and the risk of developing coronary heart disease from June 2015 to May 2023. Two independent reviewers reviewed the titles and abstracts of the records. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline to conduct the systematic review and meta-analysis. Data for the bibliometric analysis was obtained from the Scopus database and analyzed using VOSviewer and Bibliometrix applications. Six studies involving 104,511 patients were included in the final qualitative review and meta-analysis after screening the records. The prevalence of loneliness ranged from 5 to 65.3%, and social isolation ranged from 2 to 56.5%. A total of 5073 cardiovascular events were recorded after follow-up, ranging between 4 and 13 years. Poor social relationships were associated with a 16% increase in the risk of incident CVD (Hazard Ratio of new CVD when comparing high versus low loneliness or social isolation was 1.16 (95% Confidence Interval (CI) 1.10–1.22). The bibliometric analysis shows a rapidly growing field (9.77% annual growth) with common collaboration (6.37 co-authors/document, 26.53% international). The US leads research output, followed by the UK and Australia. Top institutions include University College London, Inserm, and the University of Glasgow. Research focuses on "elderly," "cardiovascular disease," and "psychosocial stress," with recent trends in "mental health," "social determinants," and "COVID-19". Social isolation and loneliness increase the risk of and worsen outcomes in incident cardiovascular diseases. However, the observed effect estimate is small, and this may be attributable to residual confounding from incomplete measurement of potentially confounding or mediating factors. The results of the bibliometric analysis highlight the multidimensional nature of CVD research, covering factors such as social, psychological, and environmental determinants, as well as their interplay with various demographic and health-related variables.

Appendix 2: Overview of studies included in the review focusing on the outcome measures, number of events, additional adjusted models and the main results

Freak-Poli 2021
The main outcomes were incident CVD and fatal CVD, and subtypes are major adverse cardiovascular events (MACE), heart failure hospitalization, MI and stroke.
Additional models adjusting for sociodemographic, lifestyle and depressive symptoms Individuals with poor social health were 42 % more likely to develop CVD (p = 0.01) and twice as likely to die from CVD (p = 0.02) over a median 4.5 years' follow-up.
Interaction effects indicated that poorer social health more strongly predicted CVD in smokers (HR 4.83, p = 0.001, pinteraction = 0.01), major city dwellers (HR 1.94, p < 0.001, p-interaction= 0.03), and younger older adults (70-75 years; HR 2.12, p < 0.001, p-interaction = 0.01).Social isolation (HR 1.66, p = 0.04) and low social support (HR 2.05, p = 0.002), but not loneliness (HR 1.4, p = 0.1), predicted incident CVD.All measures of poor social health predicted ischemic stroke (HR 1.73 to3.16).Golaszewski 2022 Major CVD including coronary heart disease, stroke, and death from CVD 1599 major CVD events Adjusting for age, race and ethnicity, educational level, and depression and relevant health behavior and health status Continuous scores of social isolation and loneliness and Hazard ratios (HRs) and 95% CIs for CVD; the HR for the association of high vs low social isolation scores with CVD was 1.18 (95% CI, 1.13-1.23),and the HR for the association of high vs low loneliness scores with CVD was 1.14 (95% CI, 1.10-1.18).The HRs after additional adjustment for health behaviors and health status were 1.08 (95% CI, 1.03-1.12;8.0% higher risk) for social isolation and 1.05 (95% CI, 1.01-1.09;5.0% higher risk) for loneliness.
Women with both high social isolation and high loneliness scores had a 13.0 % to 27.0 % higher risk of incident CVD than did women with low social isolation and low loneliness scores.

Novak 2020
CVD death, all cause of death.Second, the response categories were recoded as values, for example, "three-four" became 3.5.In the second scenario, "nine or more" was recoded as 9, "sometimes" as 2, "often" as 8, and "always" as 24.
Social isolation scales ranged from 0-21 (scenario 1) and 0-85 (scenario 2), social support from 0-20 and 0-36, and loneliness from 0-3 and 0-6.The social health composite categories were defined using the binary categories of social health as positive (not isolated, supported, and not lonely), or poor (isolated, not supported and/or lonely).

3-items for loneliness and 5-items for social isolation
The T-ILS contains the following questions: How often do you feel isolated from others?How often do you feel you lack companionship?How often do you feel left out?
The sum of the items (ranging from 3 to 9) provides a global measure of loneliness, with higher scores indicating greater loneliness.The following five indicators were included in social isolation index: (a) living alone (yes = 1 and no = 0); (b) less than monthly contact with family with whom one does not live (yes = 1and no = 0); (c) less than monthly contact with friends (yes = 1 and no = 0); (d) less than monthly contact with colleagues/ fellow students outside the workplace or school (yes = 1 and no = 0); and (e) less than monthly contact with neighbors or the local community (yes = 1 and no = 0).Using the five indicators, we generated a sum score ranging from 0 to 5, with higher scores indicating greater SI.A score between 3 and 5, corresponding to a maximum of two areas of social interfaces, was treated as an indicator of SI.CVD was defined as ischemic heart diseases (DI20-DI25), heart failure (DI150), peripheral artery occlusive disease (DI170-DI174), and stroke (DI160-DI164).

Feifei 2020
Loneliness and social isolation.Loneliness was measured using the three-item subscale from the revised University of California, Los Angele s loneliness scale.Social isolation was measured using five-item Shankar index.

3-item s for loneliness and 5-items for social isolation
The questions for loneliness include: (1) How often do you feel lack companionship?
(2) How often do you feel isolated from others?
(3) How often do you feel left out?Responses to each question were scored on a 3-point Likert scale ranging from hardly ever/never, to some of the time, to often.
Using the sum score, we had a loneliness scale ranging from 3 to 9, with a higher score indicating increased loneliness.The distribution of loneliness was positively skewed (skewness=1.25).
In Lack of instrumental or emotional support was defined as one of the latter two categories; for financial support, refusal of offered support was additionally classified as lack of support.The index includes three types of ties: (1) marital status/cohabitation, (2) contacts with close friends/family and (3) affiliation with voluntary associations.These types of ties each scored from 0 to 2, thus the index ranged from 0 to 6. Marital status/cohabitation was scored as 0 if the participant was single, divorced or widowed and 2 if the subject was married or living with a partner.Contacts with close friends and family was scored as 0 in case of 0-2 contacts, 1 in case of 3-11 contacts and 2 in case of ≥12 contacts.Affiliation with voluntary associations was defined by membership in any of six types of political, religious, community, sports or professional organizations and scored as 0 in case of no membership, 1 in case of membership in one organization, and two in case of membership in ≥2 organizations.The social integration index was categorized into four levels: level I included persons who scored 0 or 1, and levels II, III and IV included persons who scored 2-3, 4-5 and 6, respectively.We defined lack of social integration (social isolation) by level I.