Introduction
The growth of aging population in Iran is increasing like other developing countries. According to the 2016 census in Iran, approximately 9.3% of the total population had age of 60 years or higher. The rate of the elderly population in Iran is projected to reach 24% until 2049 [1]. Aging affects the physical, psychological and social health of older adults [2]. Social roles and social support are the important dimensions of social health which are affected by the increase of age. Retirement and the consequent loss of professional and social roles, death or separation from the spouse, friends and other relatives, being sent to nursing homes by children and encountering empty-nest elderly are among the common events of aging period [3, 4]. The loss of interpersonal relationships leads to anxiety, fear of loss, and loneliness in older adults [5]. On the other hand, the process of modernization in large cities has limited the access to social resources for the older adults [6]. Inhibiting the elderly's access to social networks exposes them at risk of social isolation [7]. Social isolation is defined as the lack of interactions and communications with family, friends and others [4]. More than 40% of older adults are at risk of social isolation [8, 9]. The prevalence of social isolation in older adults is 17% in British Columbia, Canada [10], 53.04% in Finland [11] and 49.8% in Malaysia. The social isolation is a strong predictor of mortality and morbidity in the elderly population [4]. It is associated with a decrease in mental health and an increase in symptoms of depression and anxiety [9], impaired cognitive function, sleep, memory, and increased suicide rate in older adults [4, 8]. There is also a high risk of chronic diseases such as hypertension and cardiovascular diseases [4, 12].
The two variables of marital status (being single) and high level of education have been reported to be effective factors in reducing social isolation of individuals [13]. Increased age and marital status (being single) are associated with more social isolation in older adults [14]. Most studies conducted worldwide have used the lubben social network scale (LSNS-6) to examine the social isolation in older adults; however, these studies indicated different results. The cultural differences indicates the importance of studying the factors related to social isolation in different parts of the world [4, 10, 15, 16, 17, 18]. To the best of our knowledge, there is scant research in the field of social isolation in older adults and non-representative populations. Therefore, the present study aims to investigate the prevalence of social isolation in older adults in Tehran, Iran, and its associated factors.
Materials and Methods
This is a secondary data analysis study. Data were related to older adults aged >60 years (n=1280) extracted from a cross-sectional study conducted by the Deputy for Research and Technology of the University of Social Welfare and Rehabilitation Sciences. The study population included all older adults in Tehran, Iran in 2020, and the data were collected from December to February 2020. The study power was calculated 97% by Cochran’s formula 1, considering a social isolation prevalence of 40% among older adults at 95% confidence interval [4]. Samples were selected from all 22 districts of Tehran using random sampling method. After visiting neighborhood associations and obtaining informed consent from them, data collection was done by six trained questioners with high inter-agreement using a checklist. The inclusion criteria were age over 60 years and living at home. The exclusion criteria were inability to understand the questions and giving incomplete answers. Hence, individuals with the abbreviated mental test score less than 7 were not included in the study [19].


We used the LSNS-6 to measure social isolation. It is a valid and reliable tool for measuring the size, closeness, and frequency of contact with social networks (family and friends) developed by Lubben in 1988. This questionnaire is a summary form of the Berkman-Syme Social Network Index [20]. The LSNS-6 evaluates the social network of family and friends separately with three items rated on a six-point Likert scale (0= none, 1= one person, 2= two people, 3= three and four people, 4= five to 8 people, and 5= nine people and more). The scale score ranges from 0 to 30. According to this scale, individuals with less than two people to see and contact with are exposed to social isolation. Its cut-off point is less than 12 [20]. The validity and reliability of the Persian version of LSNS-6 have been evaluated by Tavakoli et al. in 2016 [21] on 200 older adults aged 60 years and older in Bojnourd, Iran. The Cronbach’s alpha was reported 0.896 and the model had good fit in two dimensions, the social networks with friends and family, which confirmed its validity. In the current study, according to Sadeghi and Zanjari [22], the place of residence was divided into two developed and undeveloped areas. The relationship of socio/economic/demographic/heath variables with social isolation was analyzed in SPSS v. 23 software, considering a significance level of P<0.05.
Results 
The data of 1280 samples with a mean age of 70.97±8.07 were used in this study; 50.1% were male. The age, gender, number of children, hypertension, mental and memory problems, and the use of wheelchairs, crutches and walkers had no significant relationship with social isolation based on a binary analysis using chi-square test. According to the results in Table 1, the variables of living arrangements, marital status, income level, educational level, employment, respiratory problems, musculoskeletal problems, vision problems, hyperlipidemia, and wearing glasses had a significant relationship with social isolation (P<0.05). 




The variables that were significant based on binary analysis, the variables with P<0.2 [23], and age and gender (although they were not significant in binary analysis, but had determining roles) entered into the logistic regression model. Of two independent variables of wearing glasses and vision problems with a correlation more than 0.8, only the vision problems was included in the model. The results of multivariate logistic regression (Table 2) indicated that the variables such as gender (being male), living with spouse, household income, employment status, living in developed regions, and having cardiovascular disease, diabetes and hyperlipidemia were at a significant level; therefore, it can be said that those with male gender (P<0.05, OR=1.78), having cardiovascular disease (P<0.05, OR=1.42), having diabetes (P<0.05, OR=1.41), being retired (P<0.001, OR=2.13), being housekeeper (P<0.05, OR=2.55), and living in more developed areas (P<0.001, OR=2.02) were at more risk of social isolation.





Discussion 
This study was conducted to examine the prevalence and associated factors of social isolation among 1280 older adults aged ≥60 years in Tehran, Iran. The prevalence of social isolation was estimated 30.7%, indicating that a high number of older adults in Tehran are at risk of social isolation. This is consistent with the results of various studies that reported the prevalence of social isolation from 10 to 43% [4, 8, 9, 17, 18]. Different prevalence of social isolation in different countries, despite the use of same assessment tools, can be due to conducting study on specific or more limited populations [16, 17] with different accessibility to social and communication networks. In addition, studies have indicated that the support level for social networks varies in different countries [4, 24].
The results of our study showed that men experienced social isolation more than women which is consistent with the results of previous studies [10, 25]. It seems that women are highly able to maintain their social relations without the presence of a partner by the use of social media [14]. The relationship between age and social isolation was not significant, which is consistent with the results of most previous studies [4, 13, 16, 26], but contrary to the results of some studies [14, 25]. There are contradictory results due to the use of different assessment tools [4] or the difference in social support for the older adults in different cultures [24]. Living with spouse showed a statistically significant relationship with social isolation which is consistent with the results of previous studies [13, 14, 16, 25]. Marital satisfaction is high among the older adults; couples who have high marital satisfaction have a higher level of mental and social health [27]. Moreover, the retired and housekeeper groups of older adults in our study were at higher risk of social isolation compared to employed peers, which is consistent with the results of a previous study [13]. Employed older people have more opportunities for social interaction and have higher level of health, which leads to increased social participation [28, 29]. The result regarding the predictive power of lower household income level is similar to the results of studies conducted in Maryland, Colombia and Lebanon, which showed its association with the risk of social isolation [10, 16, 25]. A study also showed a strong relationship between the mental health and income level in the Iranian elderly, which is possibly associated with the increase in social interactions [30].
Older people living in developed areas of Tehran were more possible to experience social isolation, which is consistent with the results of previous studies [4, 31] but against the results of other studies [32, 33]. It is possible that the number of older adults referred to the neighborhood association is lower in developed areas (possibly due to retirement or movement to other areas due to reduced income or death of friends) [4]. Older adults with cardiovascular diseases in Tehran were more possible to be socially isolated, which is against the results of some studies [7, 15, 18]. However, some studies have indicated that chronic health problems in the elderly increase with social isolation [4, 16, 34, 35] which is probably due to the lower strength and physical activity of older adults with chronic diseases such as cardiovascular diseases that can lead to less contact with social networks [36]. Older adults with diabetes were also at higher risk of social isolation, which is consistent with the results of some studies [4, 37]. There is a significant relationship between mental health problems and insomnia in older adults with diabetes; diabetes may reduce vitality [38] and, thus, social interactions in older adults. In our study, older adults with hyperlipidemia were at lower risk of social isolation. Probably there was an negative relationship between high blood fat and social isolation in the cross-sectional study from which the data were extracted.
Conclusion 
Gender (male), low household income, unemployment (being retired or housekeeper), living in developed areas, having cardiovascular diseases and diabetes are associated with risk of social isolation in older adults. Policymakers and health professionals should develop educational programs to moderate the effect of these factors. 

Ethical Considerations
Compliance with ethical guidelines
This study obtained its ethical approval form the ethics committee of the University of Social Welfare and Rehabilitation Sciences (Code: IR.USWR.REC.1400.036).

Funding
The study was extracted from the master thesis of first author. This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
Conceptualization, editing and review: Niloufar Mahmoudi, Yadollah Abolfathi Momtaz; Writing: Niloufar Mahmoudi; Supervision and project administration: Yadollah Abolfathi Momtaz, Mahshid Foroughan, Nasibeh Zanjari, Seyed Hossein Mohaqeqi Kamal.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
We would like to thank the University of Social Welfare and Rehabilitation Sciences for its financial support of research.


References

1. Khodamoradi A, Hassanipour S, DaryabeigiKhotbesara R, Ahmadi B. [The trend of population aging and planning of health services for the elderly: A review study (Persian)]. Journal of Torbat Heydariyeh University of Medical Sciences(Journal of Health Chimes). 2018; 6(3):81-95. [Link]
2. World Health Organization. World report on ageing and health. Geneva: World Health Organization; 2015. [Link]
3. Nodehi Moghadam A, Rashid N, Hosseini Ajdad Niaki SJ, Hosseinzadeh S. Evaluation of quality of life and its related factors in elderly in Mashhad in 1396. Iranian Journal of Ageing. 2019; 14(3):310-9. [Link]
4. Askari Z, Mohammad T, Ahangari E. [The effectiveness of group therapy based on acceptance and commitment to quality of life in elderly people with nasal syndrome (Persian)]. Journal of Sabzevar University of Medical Sciences. 2019; 26(5):585-91. [Link]
5. Khademi MJ, Rashedi V, Sajadi S, Gheshlaghi SM. Anxiety and loneliness in the Iranian older adults. International Journal of Psychology and Behavioral Sciences. 2015; 5(2):49-52. [Link]
6. Shalchi S. [Social isolation, urban development, and socioeconomic status in Tehran (Persian]. Quarterly Journal of Social Sciences. 2018; 81(27):1-35. [Link]
7. Seyfzadeh A, Hagighatian M, Mohajerani A. The relationship between social isolation and health among the Tehranian elderly. Journal of Education and Community Health. 2017; 4:19-25. [DOI:10.21859/jech.4.3.19]
8. Ibrahim R, Abolfathi Momtaz Y, Hamid TA. Social isolation in older M alaysians: Prevalence and risk factors. Psychogeriatrics. 2013; 13(2):71-9. [DOI:10.1111/psyg.12000] [PMID]
9. Nicholson NR. A review of social isolation: An important but underassessed condition in older adults. The Journal of Primary Prevention. 2012; 33(2-3):137-52. [DOI:10.1007/s10935-012-0271-2] [PMID]
10. Taylor HO, Taylor RJ, Nguyen AW, Chatters L. Social isolation, depression, and psychological distress among older adults. Journal of Aging Health. 2018; 30(2):229-46. [PMID]
11. Kobayashi KM, Cloutier-Fisher D, Roth M. Making meaningful connections: A profile of social isolation and health among older adults in small town and small city, British Columbia. Journal of Aging Health. 2009; 21(2):374-97. [PMID]
12. Tsuji T, Saito M, Ikeda T, Aida J, Cable N, Koyama S, et al. Change in the prevalence of social isolation among the older population from 2010 to 2016: A repeated cross-sectional comparative study of Japan and England. Archives of Gerontology and Geriatrics. 2020; 91:104237. [PMID]
13. Gilmour H, Ramage-Morin PL. Social isolation and mortality among Canadian seniors. Health Reports. 2020; 31(3):27-38. [PMID]
14. Tanskanen J, Anttila T. A prospective study of social isolation, loneliness, and mortality in Finland. American Journal of Public Health. 2016; 106(11):2042-8. [DOI:10.2105/AJPH.2016.303431] [PMID] [PMCID]
15. Vozikaki M, Papadaki A, Linardakis M, Philalithis A. Social isolation and well-being among older adults in Europe. Archives of Hellenic Medicine. 2018; 35(4):506-19. [Link]
16. Merchant RA, Liu SG, Lim JY, Fu X, Chan YH. Factors associated with social isolation in community-dwelling older adults: A cross-sectional study. Quality of Life Research. 2020; 29(9):2375-81. [DOI:10.1007/s11136-020-02493-7] [PMID]
17. Rezaei Nasab Z, Fotohi S. [Study of gender differences in social isolation and its effective factors in Tehran (Persian)]. Urban sociological studies. 2018; 8(26):127-60. [Link]
18. Seyfzadeh A, Haghighatian M, Mohajerani A A. [Economic, social and demographic characteristics and social isolation in senile people (case study: Tehran City) (Persian)]. Middle Eastern Journal of Disability Studies. 2019; 9:23. [Link]
19. Boulos C, Salameh P, Barberger-Gateau P. Social isolation and risk for malnutrition among older people. Geriatrics & Gerontology International. 2017; 17(2):286-94. [PMID]
20. Ha JH, Hougham GW, Meltzer DO. Risk of social isolation among older patients: What factors affect the availability of family, friends, and neighbors upon hospitalization? Clinical Gerontologist. 2019; 42(1):60-9. [PMID]
21. Shimada K, Yamazaki S, Nakano K, Ngoma AM, Takahashi R, Yasumura S. Prevalence of social isolation in community-dwelling elderly by differences in household composition and related factors: From a social network perspective in urban Japan. Journal of Aging and Health. 2014; 26(5):807-23. [PMID]
22. Kalantari A, Hoseynizadeharani SS. [City and social relationships: A Study of the relationship between social isolation and level of received social support with the experience of loneliness (Case Study: Tehran residents) (Persian)]. Urban Studies. 2015; 5(16):87-118. [Link]
23. Ebrahimi P, Afshani A, Hassani Darmian Gh, Kermani M. [Comparative study of the effect of social isolation on the health of citizens Mashhad (Persian)]. Scientific Quarterly of Khorasan Socio-Cultural Studies. 2019; 13(3):7-44. [Link]
24. Asadi-Lari M, Vaez-Mahdavi MR, Faghihzadeh S, Cherghian B, Esteghamati A, Farshad AA, et al. Response-oriented measuring inequalities in Tehran: second round of UrbanHealth Equity Assessment and Response Tool (Urban HEART-2), concepts and framework. Medical Journal of the Islamic Republic of Iran. 2013; 27(4):236-48. [PMID]
25. Bakhtiyari F, Foroughan M, Fakhrzadeh H, Nazari N, Najafi B, Alizadeh M, et al. [Validation of the persian version of Abbreviated Mental Test (AMT) in elderly residents of Kahrizak charity foundation (Persian)]. Iranian journal of Diabetes and Metabolism. 2014; 13(6):487-94. [Link]
26. Wu CS, Lai MS, Gau SS, Wang SC, Tsai HJ. Concordance between patient self-reports and claims data on clinical diagnoses, medication use, and health system utilization in Taiwan. PloS One. 2014; 9(12):e112257. [PMID]
27. Gupta V, Gu K, Chen Z, Lu W, Shu XO, Zheng Y. Concordance of self-reported and medical chart information on cancer diagnosis and treatment. BMC Medical Research Methodology. 2011; 11:72. [DOI:10.1186/1471-2288-11-72] [PMID]
28. Mohaqeqi Kamal S H, Basakha M. Prevalence of chronic diseases among the elderly in Iran: Does socioeconomic status matter? (Persian)] Salmand: Iranian Journal of Ageing. 2002; 16(4):468-81. [Link]
29. Lubben J, Blozik E, Gillmann G, Iliffe S, von Renteln Kruse W, Beck JC, et al. Performance of an abbreviated version of the Lubben Social Network Scale among three European community-dwelling older adult populations. Gerontologist. 2006; 46(4):503-13. [PMID]
30. Tavakoli Ghouchani H, Lashkardoost H, Khankolabi M, Asghari D, Hekmatara E, Nabavi SH. [Validity and reliability of Persian Version of Lubben Social Netwok-6 Scale in elderly adult (Persian)]. Journal of North Khorasan University of Medical Sciences. 2020; 12(2):64-9. [Link]
31. Sadeghi R, Zanjari N. [The inequality of development in the 22 districts of Tehran metropolis (Persian)]. Social Welfare Quarterly. 2017; 17(66):149-84. [Link]
32. Marrone G, Abdul-Rahman L, De Coninck Z, Johansson A. Predictors of contraceptive use among female adolescents in Ghana. African Journal of Reproductive Health. 2014; 18(1):102-9. [PMID]
33. Taylor RJ, Chatters LM, Woodward AT, Brown E. Racial and ethnic differences in extended family, friendship, fictive kin, and congregational informal support networks. Family Relations. 2013; 62(4):609-24. [PMID]
34. Asadi Noghabi A, Alhani F, Peyrovi H. The concept of health in elderly people: A literature review. Iran Journal of Nursing. 2012; 25(78):62-71. [Link]
35. Cudjoe TKM, Roth DL, Szanton SL, Wolff JL, Boyd CM, Thorpe RJ. The epidemiology of social isolation: National health and aging trends study. The Journals of Gerontology: Series B. 2020; 75(1):107-13. [PMID]
36. Zarei H, Abolfathi Momtaz Y, Sahaf R, Mehdi M. [Marital satisfaction among older adults who married in old age in sanandaj in 2016 (Persian)]. Salmand: Iranian Journal of Ageing. 2019; 14(1):14-25. [Link]
37. Borhaninejad V, Nabvi S, Lotfalinezhad E, Amini F, Mansouri T. [Relationship between Social participation and life satisfaction among older people (Persian)]. Journal of North Khorasan University of Medical Sciences. 2017; 8(4):701-11. [DOI:10.18869/acadpub.jnkums.8.4.701]
38. Tan ME, Sagayadevan V, Abdin E, Picco L, Vaingankar J, Chong SA, et al. Employment status among the S ingapore elderly and its correlates. Psychogeriatrics. 2017; 17(3):155-63. [PMID]
39. Alizadeh M, Hoseini M, Shojaeizadeh D, Rahimi A, Arshinchi M, Rohani H. [Assessing anxiety, depression and psychological wellbeing status of urban elderly under represent of Tehran metropolitan city (Persian)]. Salmand: Iranian Journal of Ageing. 2012; 7(3):66-73. [Link]
40. Henning‐Smith C, Moscovice I, Kozhimannil K. Differences in social isolation and its relationship to health by rurality. The Journal of Rural Health. 2019; 35(4):540-9. [PMID]
41. Crowe C, Kwon D, Belsky D. Association of loneliness and social isolation with healthspan and lifespan in the US health and retirement study. Innovation in Aging. 2020; 4(Supplement_1):166. [PMCID]
42. Barnes TL, MacLeod S, Tkatch R, Ahuja M, Albright L, Schaeffer JA, et al. Cumulative effect of loneliness and social isolation on health outcomes among older adults. Aging & Mental Health. 2021; 1-8. [PMID]
43. Borji M, Bastami M, Bastami Y, Azami M, Tavan H. [Physical activity among elderly people with heart disease (Persian)]. Iran Journal of Cardiovascular Nursing. 2015; 4(2):54-61. [Link]
44. Xia N, Li H. Loneliness, social isolation, and cardiovascular health. Antioxidants & Redox Signaling. 2018; 28(9):837-51. [PMID]
45. Mansouri T, Farhadi A, Borhaninejad V R, Kojaie Bidgoli A, Navvabi Rigi S D, Hosseinabadi R. [Factors and barriers affecting the social participation of older people (Persian)]. Journal of North Khorasan University of Medical Sciences. 2018; 9(4):66-73. [Link]
46. Alcaraz KI, Eddens KS, Blase JL, Diver WR, Patel AV, Teras LR, et al. Social isolation and mortality in US black and white men and women. American Journal of Epidemiology. 2019; 188(1):102-9. [PMID]
47. Fadayevatan R, Bahrami M, Mohamadzadeh M, Borhaninejad V. [Relationship of sleep quality with mental health and blood sugar control in elderly people with diabetes mellitus (Persian)]. Salmand: Iranian Journal of Ageing. 2020; 14(4):380-91. [Link]
48. Moghaddas F, Khamnian Z. [The prevalence of obesity, hypertension, diabetes and hyperlipidemia among elderlies over 60 years of age of Sahlan area in Tabriz (Persian)]. Depiction oF Health. 2018; 9:206-13. [Link]
49. Hajek A, König HH. The association between obesity and social exclusion in middle-aged and older adults: findings from a nationally representative study in Germany. BMC geriatrics61. 2018; 18(1):258. [Link]