Introduction
Today, with the dramatic increase in the number of elderly people, population aging and its consequences have become one of the most important public health challenges [1]. Loneliness, as an important health indicator, has a role in increasing the incidence and aggravation of mental and physical diseases in the elderly. Factors such as reduced social interactions and declined performance are related to the feeling of loneliness in the elderly [4, 5, 10]. On the other hand, depression is one of the common and important disorders in the elderly, which has adverse effects on their individual performance; depressed elderly with the highest degree of loneliness experience social isolation. Since the depressed older people interprets the issues from their own perspective according to the cognitive model, depression has become one of the most important debilitating disorders in the elderly [10, 23]. In this study, we assess the mediating role of depression in the relationship between feeling of loneliness and social functioning in the elderly.
Methods
In this correlational cross-sectional study, 318 older adults covered by the comprehensive health centers of Bushehr (south of Iran) were selected by simple random sampling method in 2018 based on the inclusion criteria. To collect data, in addition to the demographic form, Russell’s UCLA Loneliness Scale (third version) with items rated on a 4-point Likert scale (from 1 to 4) and Goldberg’s 28-item general health questionnaire (subscales of depression and social dysfunction) with items rated on a 4-point Likert scale from 0 to 3, were used. In the present study, Cronbach’s alpha of UCLA Loneliness Scale was obtained 0.92; for depression and social dysfunction subscales, it was obtained 0.86 and 0.79, respectively. For the illiterate participants, the questionnaires were completed by the researcher. The questionnaires took about 20 min to complete. To analyze the data, the partial least squares-structural equation modeling was performed in PLS Graph v.3.00 software. PLS is a robust and powerful statistical method [37]. The bootstrap method with 5000 times of resampling was used to access the t-statistic and confidence interval. Cronbach’s alpha and composite reliability were used to estimate reliability. Average variance extracted (AVE) was used to estimate convergent validity, and Fornell Locker and heterotrait-monotrait criteria were used to estimate the discriminant validity of the external model. The fit of the internal model was evaluated using the coefficient of determination and Stone-Geisser’s Q² value [38].
Results
The mean age of participants was 66.74±5.87 years ranged 60-87 years; 75% aged <75 years and 55.3% were male. The external and internal model fit indices indicated the appropriateness of the model. The results showed that for all three variables, Cronbach’s alpha and composite reliability were more than 0.7 and the value of AVE was more than 0.5, which are acceptable. For some items, the factor loads were between 0.4 and 0.7, but were kept because removing them did not have much effect on the reliability of the items. The correlation coefficient between two variables was lower than the square root of the AVE, which indicates appropriate discriminant validity. Based on the heterotrait-monotrait criterion, discriminant validity was below 0.9 in all items, which is acceptable.
The amount of direct, indirect and total effects as well as the t-statistics are given in Table 1.


The results showed that feeling of loneliness could lead to poor social functioning directly (p<0.01 and β=0.199) and through mediation by depression (p<0.001 and β=0.183). Feeling of loneliness explained 36% of the variance in depression. In addition, the feeling of loneliness and depression together explained 20% of the variance in social dysfunction. Internal model variables did not have multiple collinearity. The minimum and maximum VIF for internal model variables were 1 and 1.55, respectively. Stone-Geisser’s Q² value for the two variables of depression and social dysfunction was 0.391 and 0.367, respectively, which indicates the good fit of the internal model.
Discussion
The results of this study revealed that the feeling of loneliness directly and through mediation by depression can lead to poor social functioning in the elderly. The problems of old age cause the elderly to become marginalized and turn them from having an active role to having a passive role, and cause dissatisfaction, loneliness, depression, and consequently, a decrease in their personal and social activities [40]. Depressed older adults make less effort to establish their social relationships due to the decrease in energy, motivation and change in their attitude towards issues; these changes gradually reduce their social interactions [20]. Planning by health care providers to optimally fill the time of the elderly, training the elderly to create and increase relationships with the people around them, as well as family-oriented training on how to interact with the elderly can reduce the feeling of loneliness in them and lead to reducing depression and improving social functioning.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the research ethics of Bushehr University of Medical Sciences (Code: IR.BPUMS.REC.1397.087). Informed consent was obtained from participants.

Funding
This study was extracted from the master thesis of first author, and funded by Bushehr University of Medical Sciences.

Authors' contributions
Conceptualization and data collection: Roya Zakizadeh and Masoud Bahreini; data analysis: Razieh Bagherzadeh; data interpretation: Masoud Bahreini, Akram Farhadi, Razieh Bagherzadeh; final approval: All authors.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors would like to thank all seniors participated in the study and the Vice-Chancellor for research of Bushehr University of Medical Sciences for their cooperation and support.

References

1. Hojjati H, Sharifnia H, Hassanalipour S, Akhonzadeh G, Asayesh H. [The effect of reminiscence on the amount of group self-esteem and life satisfaction of the elderly (Persian)]. Nursing and Midwifery Journal. 2011; 9(5):350-6. [Link]
2. Zhang Y, Chen Y, Ma L. Depression and cardiovascular disease in elderly: Current understanding. Journal of Clinical Neuroscience. 2018; 47:1-5. [DOI:10.1016/j.jocn.2017.09.022] [PMID]
3. Statistical Center of Iran. Selected Results of the 2016 National Population and Housing Census. Tehran: Statistical Center of Iran; 2017. [Link]
4. Tian Q. Intergeneration social support affects the subjective well-being of the elderly: Mediator roles of self-esteem and loneliness. Journal of Health Psychology. 2016; 21(6):1137-44. [DOI:10.1177/1359105314547245] [PMID]
5. Schutter N, Holwerda T, Stek M, Dekker J, Rhebergen D, Comijs H. Loneliness in older adults is associated with diminished cortisol output. Journal of Psychosomatic Research. 2017; 95:19-25. [DOI:10.1016/j.jpsychores.2017.02.002] [PMID]
6. Chen YH, Lin LC, Chuang LL, Chen ML. The relationship of physiopsychosocial factors and spiritual well-being in elderly residents: Implications for evidence-based practice. Worldviews on Evidence-Based Nursing. 2017; 14(6):484-91. [DOI:10.1111/wvn.12243] [PMID]
7. Heravi-karimloo M, Anoosheh M, Foroughan M. [Loneliness from the perspectives of elderly people: a phenomenology study (Persian)]. Salmand: Iranian Journal of Ageing. 2008; 2(6):410-20. [Link]
8. Suedfield P. Pastthe reflection and through the looking glass: Extending loneliness research. Journal of Social Behavior and Personality. 1987; 2(2):51. [Link]
9. Heinrich LM, Gullone E. The clinical significance of loneliness: A literature review. Clinical Psychology Review. 2006; 26(6):695-718. [DOI:10.1016/j.cpr.2006.04.002] [PMID]
10. Ghasemi Pirbalouti M, shariat A, Ghazanfari A. [A meta-analysis of exercise therapy on reducing depression among older adults in Iran (Persian)]. Quarterly Journal of Health Psychology. 2019; 8(2):69-80. [DOI:10.30473/HPJ.2019.40010.3982]
11. Kavoosian N, Hosseinzadeh K, Jaliseh HK, Karboro A. [The relationship between spiritual health and loneliness among the elderly in Karaj-2016 (Persian)]. Journal of Research on Religion & Health. 2018; 4(2):7-15. [Link]
12. Panayiotou G, Panteli M, Theodorou M. Predictors of loneliness in a sample of college men and women in cyprus: The role of anxiety and social skills. Psychology, Community & Health. 2016; 5(1):16-30. [DOI:10.5964/pch.v5i1.142]
13. Theeke LA. Predictors of loneliness in US adults over age sixty-five. Archives of Psychiatric Nursing. 2009; 23(5):387-96. [DOI:10.1016/j.apnu.2008.11.002] [PMID]
14. Wong N, Liu H, Lin C, Huang CM, Wai Y, Lee S, et al. Loneliness in late-life depression: Structural and functional connectivity during affective processing. Psychological Medicine. 2016; 46(12):2485-99. [DOI:10.1017/S0033291716001033] [PMID]
15. Masi CM, Chen HY, Hawkley LC, Cacioppo JT. A meta-analysis of interventions to reduce loneliness. Personality and Social Psychology Review: An Official Journal of the Society for Personality and Social Psychology, Inc. 2011; 15(3):219-66. [DOI:10.1177/1088868310377394] [PMID] [PMCID]
16. Alavi M, Jorjan Shushtari Z, Noroozi M, Mohammadali Shahboulaghi F. [Mental health and related factors in old papulation in Tehran 2014-2015 (Persian)]. Jornal Mazandaran University of Medical Sciences. 2018; 27(158):112-22. [Link]
17. Rao S, Wallace L, Theou O, Rockwood K. Is it better to be happy or not depressed? Depression mediates the effect of psychological well‐being on adverse health outcomes in older adults. International journal of Geriatric Psychiatry. 2017; 32(9):1000-8. [DOI:10.1002/gps.4559] [PMID]
18. Maghsoudnia S. [Primary health care for old adults in IR Iran (Persian)]. Tehran: University of Social Welfars and Rehabilitation of Science; 2011.
19. Creecy RF, Berg WE, Wright R. Loneliness among the elderly: A causal approach. Journal of Gerontology. 1985; 40(4):487-93. [DOI:10.1093/geronj/40.4.487] [PMID]
20. Copeland JR, Beekman AT, Braam AW, Dewey ME, Delespaul P, Fuhrer R, et al. Depression among older people in Europe: the EURODEP studies. World psychiatry. 2004; 3(1):45-9. [PMCID]
21. Bagherinezhad M, Salehi Fadardi J, Tabatabaee S. [Relationship between rumination and depression in a sample of Iranian students (Persian)]. Studies in Education & Psychology 2010; 11(1):21-38. [Link]
22. Sadock BJ. Sadock’s synopsis of psychiatry: Behavioral sciences [F. Rezaee, Persian trans.].Tehran: Arjmand pub; 2015.
23. Manzouri L, Babak A, Merasi M. [Thedepression status of the elderly and it’s related factors in Isfahan in 2007 (Persian)]. Salmand: Iranian Journal of Ageing. 2010; 4(4):27-33. [Link]
24. Theeke LA, Mallow J. Loneliness and quality of life in chronically Ill rural older adults: Findings from a pilot study. The American Journal of Nursing. 2013; 113(9):28-38. [DOI:10.1097/01.NAJ.0000434169.53750.14] [PMID] [PMCID]
25. Solmi M, Veronese N, Galvano D, Favaro A, Ostinelli EG, Noventa V, et al. Factors associated with loneliness: an umbrella review of observational studies. Journal of Affective Disorders. 2020; 271:131-8. [DOI:10.1016/j.jad.2020.03.075] [PMID]
26. Igbokwe CC, Ejeh VJ, Agbaje OS, Umoke PIC, Iweama CN, Ozoemena EL. Prevalence of loneliness and association with depressive and anxiety symptoms among retirees in Northcentral Nigeria: a cross-sectional study. BMC Geriatrics. 2020; 20(1):153. [DOI:10.1186/s12877-020-01561-4] [PMID] [PMCID]
27. Mirderikvand F, Adavi H, Amirian L, Khodaie S. [The Investigation relationship between Social support and Depression mediated by Loneliness between Elderly (Persian)]. Journal of Geriatric Nursing. 2018; 3(2):63-75. [DOI:10.21859/jgn.3.2.63]
28. Faronbi JO, Gustafsson S, Berglund H, Ottenvall Hammar I, Dahlin-Ivanoff S. Social network and support, self-rated health, and loneliness as predictors of risk for depression among pre-frail and frail older people in Sweden. Journal of Gerontology & Geriatric Medicine. 2017; 2(5). [Link]
29. Santini ZI, Fiori KL, Feeney J, Tyrovolas S, Haro JM, Koyanagi A. Social relationships, loneliness, and mental health among older men and women in Ireland: A prospective community-based study. Journal of Affective Disorders. 2016; 204:59-69. [DOI:10.1016/j.jad.2016.06.032] [PMID]
30. Alberti FB. A biography of loneliness: The history of an emotion. Oxford: Oxford University Press; 2019. [Link]
31. Zakizadeh R, Bahreini M, Farhadi A, Bagherzadeh R. Predictive role of loneliness in mental health of elderly people in Bushehr (Persian)]. Iranian Journal of Psychiatric Nursing. 2020; 7(6):71-8. [Link]
32. Arslantaş H, Adana F, Ergin FA, Kayar D, Acar G. Loneliness in elderly people, associated factors and its correlation with quality of life: A field study from Western Turkey. Iranian Journal of public health. 2015; 44(1):43-50. [PMCID]
33. Malekooti SK, Mirabzadeh A, Fathollahi P, Salavati M, Kahali S, Afkham Ebrahimi A, et al. [Reliability, validity and factor structure of the GHQ-28 in Iranian elderly (Persian)]. Iranian Journal of Ageing. 2006; 1(1):11-21. [Link]
34. Russell DW. UCLA Loneliness Scale (Version 3): Reliability, validity, and factor structure. Journal of personality assessment. 1996; 66(1):20-40. [DOI:10.1207/s15327752jpa6601_2] [PMID]
35. Younesi J. The role of cognitive distortion (Deterministic thinking) on Psychological pathology. Iranian Association of Psychology. 2004; 3(12):73-86. [Link]
36. Sodani M, Shogaeyan M, Neysi A. [The effect of group logo - therapy on loneliness in retired men (Persian)]. Journal of Research in Cognitive and Behavioral Sciences. 2012; 2(1):43-54. [Link]
37. Chin WW. The partial least squares approach to structural equation modeling. In: Marcoulides GA, editor. Modern methods for business research. New Jersey: Lawrence Erlbaum; 1998. [Link]
38. Dijkstra TK, Henseler J. Consistent partial least squares path modeling. MIS quarterly. 2015; 39(2):297-316. [DOI:10.25300/MISQ/2015/39.2.02]
39. Leitch S, Glue P, Gray AR, Greco P, Barak Y. Comparison of psychosocial variables associated with loneliness in centenarian vs elderly populations in New Zealand. JAMA network open. 2018; 1(6):e183880. [DOI:10.1001/jamanetworkopen.2018.3880] [PMID] [PMCID]
40. Moatamedi A, Qaderi Bagajan K, Mazaheri Nejad Fard G, Soltani S. [Comparative study of feeling lonely between retired and labor elderly men (Persian)]. Quarterly Journal of Social Work. 2017; 6(2):43-50. [Link]
41. Mellor D, Stokes M, Firth L, Hayashi Y, Cummins R. Need for belonging, relationship satisfaction, loneliness, and life satisfaction. Personality and Individual differences. 2008; 45(3):213-8. [DOI:10.1016/j.paid.2008.03.020]
42. Mohammadi E, Allahyari T, Darvishpoor Kakhaki A, Saraei H, Fereshtehnejad SM. [Analysis of being active based on older adults’ experience: a qualitative study of active aging strategies (Persian)]. Iranian Journal of Ageing. 2017; 11(4):504-17. [DOI:10.21859/sija-1104504]
43. Mohamadzadeh M, Rashedi V, Hashemi M, Borhaninejad V. [Relationship between activities of daily living and depression in older adults (Persian)]. Salmand: Iranian Journal of Ageing. 2020; 15(2):200-11. [DOI:10.32598/sija.13.10.180]
44. Hekmatipoor N, Hojati H, Sharifnia H, Akhondzadeh G, Nikjoo A, Mirabilhasani M. [Impact of routine exercises on elderly’s depression rate (Persian)]. Journal of Health building community health education. 2012; 1(3):23-32. [Link]
45. Nakamura M, Hashizume H, Nomura S, Kono R, Utsunomiya H. The relationship between locomotive syndrome and depression in community-dwelling elderly people. Current Gerontology and Geriatrics Research. 2017; 2017:4104802. [DOI:10.1155/2017/4104802] [PMID] [PMCID]
46. Shojaeimotlagh V, Lazari N, Ghalenoee M, Saleh Abadi S, Parizad N, Ghanei Gheshlagh R. [Relationship between metabolic syndrome and depression in elderlies with cardiovascular disease (Persian)]. Iran Journal of Nursing. 2015; 27(92):65-72. [DOI:10.29252/ijn.27.92.65]
47. Preacher KJ. Advances in mediation analysis: A survey and synthesis of new developments. Annual review of psychology. 2015; 66:825-52. [DOI:10.1146/annurev-psych-010814-015258] [PMID]