The United Nations (2017) estimated  that the world population aged 65 and older is expected to pass 2 billion and the population aged 80 and older to pass 1 billion, respectively, by 2050. As life expectancy is rapidly increasing, well-being in late life is garnering interest among researchers, physicians, mental health practitioners, and policymakers, because it is a common concern with significant consequences in terms of health care needs and economic costs.
The aging process involves the dynamic interaction of a range of biological, psychological, social, and economic changes that together impact outcomes in later life. Some of the major challenges often associated with aging include increasing physical limitations  risk of social isolation , and economic hardship related to decreased ability to earn income. Older adults who lack the resources to deal effectively with these challenges are often at risk for depression and other negative mental health outcomes .
In spite of these challenges, gerontological research in recent decades has emphasized the ways in which successful aging can be achieved, leading to positive functioning and happiness in late life. Successful aging and well-being across adulthood have become a key topic of research as the literature has highlighted the relationship of well-being with several positive life outcomes and lower rates of mortality  . Although good health and the absence of illness and disability have been determined to be important predictors of well-being , various studies have shown that subjective and spiritual well-being is affected by many other variables. These include indicators of social and economic status such as income, education, marital status, social support, and religious involvement (e.g., church attendance), as well as certain well-known psychological characteristics, personality traits and a sense of coherence .
Contrary to the negative myths that relate aging with declines in well-being, Carstensen and colleagues  suggest that older adulthood is a period of development where the well-being outcomes and emotional regulation of the elderly are improving compared to the middle-life because older adults tend to focus particularly on emotionally positive situations. Furthermore, a growing body of research reveals that involvement in religious activities affects spiritual well-being and may improve the elderly’s overall psychological well-being and the way that they judge their life satisfaction .
Therefore, this review aims to summarize the current literature on the role of well-being and spirituality/religiosity in shaping the construct of the overall satisfaction or happiness with life, revealing the strong influence of these determinants on the successful aging of older adults. This paper begins with an introduction, followed by two basic themes of the field of successful aging: a) the role of well-being, including the subjective, hedonic, and eudemonic constructs, and b) the role of spirituality and religiosity.
2. Method for Locating Articles and Selection Criteria
An electronic search of English language peer-reviewed empirical and review articles, as well as books (or book chapters), was conducted covering articles from January 01, 2000, to November 30, 2019, in the following databases: PsycINFO, Google Scholar, PubMed and Web of Science. Search terms included “successful aging”, “well-being” and “religiosity”. For inclusion, the selected studies had to reflect aninternational perspective on the field of aging and had to focus on populations from middle to older adulthood. Non-English articles, book reviews, dissertations, monographs, and letters to the editor were excluded from consideration (n = 24). Finally, this procedure provided 41 sources (which is included in the reference list) focusing specifically on the field, and included 37 articles from 31 journals plus 3 books and 1 working paper. Using a content analysis methodology, the selected articles were categorized into two separate thematic areas, which included (a) the role of well-being and (b) the role of religiosity and spirituality. These thematic areas emerged from the literature that was found important and feasible to study and they represent relevant aspects of successful aging.
3. Results of the Literature Review
3.1. Theme I: The Role of Well-Being
Well-being can be conceptualized as encompassing not only the absence of physical and mental health problems, but also a subjective sense of happiness comprising a cognitive and an affective component . Particularly in late life, it is this subjective sense of the quality of life that often has the largest impact on how one functions and sees one’s life . According to Kahneman, Diener, and Schwarz , subjective well-being has a sense of life evaluation; hedonic well-being refers to everyday feelings such as the experience of happiness, anger, or grief; and eudemonic well-being focuses on individuals’ judgments about the meaning and purpose of their life.
From the perspective of developmental psychology, older adulthood is marked by the need to develop a sense of meaning and purpose in life, as well as a need for a sense of generativity, or of having passed along something important to the next generation . A sense of meaning and purpose can be useful in buffering the effects of existential anxiety, which can become more salient in late life as growing physical limitations and the loss of loved ones cause older adults to think more about their own mortality . Numerous studies have found that experiencing meaning and purpose in life is closely related to a wide range of positive well-being outcomes  .
Another important perspective in understanding late life well-being is social connectedness. Older adults who maintain ties with other people have better well-being outcomes on numerous important dimensions  . Connectedness with others may be beneficial in a number of ways. Most directly, others may provide practical assistance in meeting daily needs (e.g., help with transportation for medical care, or help maintaining one’s house)  . More benefits, however, are likely to come from the emotional support that close social connections can provide, improving quality of life and psychological well-being . The number of social ties is not necessarily the best metric for conceptualizing this connectedness, however, as there is also evidence that older adults tend to benefit the most by focusing on a smaller number of higher-quality relationships, rather than maintaining a larger network of relatively superficial ties .
International cross-sectional surveys including data over much time period have revealed that despite decreasing health and income with age, psychological well-being may improve , verifying previous findings of a U-shaped relationship between age and well-being, with greater well-being at younger and older ages and lower well-being scores at middle life . Although gerontological research has tended to accept this finding as standard for all populations across the world, a number of studies both from developed and developing countries have found well-being to decline with age , particularly for hedonic experiences . In addition, literature on successful aging has accumulated evidence of gender gaps in the associations between education, income, marital status, and well-being, indicating that men tend to present higher outcomes on well-being and happiness with life than women , and that marriage is not always a stable predictor of satisfaction with life across adulthood , particularly for men . These findings can be explained by the fact that men tend to be more highly educated and earn higher incomes than women, which may contribute to their well-being.
3.2. Theme II: The Role of Religion and Spirituality
One important element of well-being in older adulthood involves the role of religious belief and involvement. Religion can be conceptualized as a complex and multifaceted phenomenon involving elements of belief, behavior, community involvement, and social identity . On the other hand, spirituality can be viewed as the search for interconnectedness with humanity and a personal need for connection with a higher power that can occur in and/or outside of a formal religious context . A very large number of studies have found a relationship of religious and spiritual involvement with better psychological and health outcomes , with these effects often appearing more pronounced in later life . However, large cross-cultural variations in this relationship have also been found with respect to this set of associations, with religious involvement appearing to have no impact or even a deleterious relationship with well-being outcomes in some contexts . This can be explained by the fact that the relationship between religiosity and well-being is moderated by culture, meaning that the predictive value of religiosity on well-being has been found to be lower in the context of studies with atheist samples .
One reason that religion may be especially important in influencing well-being in late life in comparison to other life stages is that it often has direct implications both for promoting a sense of existential meaning in life and for developing strong social ties, which are both critical for late-life well-being. The meaning-making functions of religion are well-established in the literature  and operate in at least two ways. First, religious groups provide their members with specific tenets that help to answer their existential questions explicitly . Second, belonging to a religious group involves interacting with a community of people who share the same existential belief system, providing a sense of consensus that serves to reinforce certainty in that system of beliefs . The existential functions of religion impact well-being in part by reducing anxiety and the risk of depression . Religious beliefs also provide the basis for a number of unique psychological coping mechanisms (such as prayer) that can provide benefits to well-being , and contribute to positive emotions and the use of appropriate strategies to regulate one’s emotions.
From a social perspective, religious involvement serves to provide older adults with a network of social connections that can be beneficial by providing emotional support and other socially-mediated benefits . Religious groups may be especially beneficial to the development of these social connections, because they are one of the few social institutions to bring together members from across the spectrum of age ranges . This gives members the opportunity to develop close social relationships that may last for decades and to play the role of an elder in cross-generational relationships.
Although its findings are interesting and significant, this review also has several limitations. First, the self-reported outcomes of the well-being of the very old participants may be affected by the respondents’ cognitive sufficiency and educational attainment. Future research should take this limitation into account and assess very old participants for cognitive impairment before recruiting them for a research study. Second, many selected studies were cross-sectional and the results may change over time. Future research should focus on longitudinal studies whose results could be generalizable at an international level. Third, because most studies include English-speaking countries whose participants were theists (e.g., Catholic, Orthodox Protestant, and Muslim), we have to be careful in generalizing the perspectives of this review to other cultural contexts with significant numbers of atheists. Although cross-religious studies have not yet been conducted, further research should be encouraged to capture a religion-specific perspective on the impact of religious involvement in the shaping of successful aging in late life .
5. Summary and Conclusions
This paper aimed to present a review of the current literature about the roles of well-being and of spirituality and religiosity in successful aging in late life. Although research into successful aging is at an earlier stage, this review provides us with strong evidence of the important contributions of subjective, hedonic, and eudemonic well-being and religious practices, including prayer and church attendance, to one’s quality of life evaluation and overall psychological health  . Previous studies have also confirmed the positive outcomes of well-being in the lives of those showing indicators of successful aging, including the domains of health and functioning, relationships with others, emotional regulation, and overall happiness with life . Furthermore, the review of the selected studies supports the notion that psychological well-being is also moderated by other key social and demographic predictors, such as gender, income, education, and marital status . Various studies around the world have verified that good health and functioning, higher income, and greater educational levels as well as being male are factors associated with positive well-being and successful aging. Among the key variables, physical health has been widely found to be related to greater well-being, while at the same time well-being may be a protective factor in maintaining better health . Finally, this paper confirmed a dichotomy in the literature of studies, mostly from English-speaking countries, reporting that as people age their well-being tends to improve compared to middle-life , and other studies suggesting a U-shaped relationship between life satisfaction and age does not exist across all populations and contexts, particularly for countries in transition and sub-Saharan countries .
Given the diversity of aging experiences across the globe, government agencies, policy makers, and mental health providers should consider the implications of these findings to identify the major issues that the most vulnerable aged people face. Furthermore, psychologists, gerontologists, and clinicians working with aged populations must be aware of the role that well-being, spirituality, religiosity, and other socio-demographic variables play as burdens or contributors in order to implement developmentally appropriate interventions to foster psychological well-being in late life.
This study was supported by the Aging Department of the Greek Association of Mental Health for Children and Adults in Greece.
 United Nations, Department of Economic and Social Affairs, Population Division (2017) World Population Prospects: The 2017 Revision, Key Findings and Advance Tables (Working Paper No. ESA/P/WP/248). United Nations, New York.
 Tesch-Römer, C. and Wahl, H.-W. (2016) Toward a More Comprehensive Concept of Successful Aging: Disability and Care Needs. The Journals of Gerontology: Series B, 72, 310-318.
 Cudjoe, T.K.M., Roth, D.L., Szanton, S.L., Wolff, J.L., Boyd, C.M. and Thorpe Jr., R.J. (2018) The Epidemiology of Social Isolation: National Health and Aging Trends Study. The Journals of Gerontology: Series B, 75, 107-113.
 Blazer, D.G. (2003) Depression in Late Life: Review and Commentary. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 58, M249-M265.
 Chida, Y. and Steptoe, A. (2008) Positive Psychological Well-Being and Mortality: A Quantitative Review of Prospective Observational Studies. Psychosomatic Medicine, 70, 741-756.
 Jivraj, S., Nazroo, J., Vanhoutte, B. and Chandola, T. (2014) Aging and Subjective Well-Being in Later Life. The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 69, 930-941.
 Galiana, L., Gutierrez, M., Sancho, P., Francisco, E.-H. and Tomas, J.M. (2016) Socio-Demographic Variables and Successful Aging of the Angola Elderly. Scientifica, 2016, Article ID: 5306756.
 Carstensen, L.L., Fung, H.H. and Charles, S.T. (2003) Socioemotional Selectivity Theory and the Regulation of Emotion in the Second Half of Life. Motivation and Emotion, 27, 103-123.
 Villani, D., Sorgente, A., Iannello, P. and Antonietti, A. (2019) The Role of Spirituality and Religiosity in Subjective Well-Being of Individuals With Different Religious Status. Frontiers in Psychology, 10, 1525.
 George, L.K. (2009) Still Happy after All These Years: Research Frontiers on Subjective Well-Being in Later Life. The Journals of Gerontology: Series B, 65B, 331-339.
 Robinson, O.C., Demetre, J.D. and Litman, J.A. (2016) Adult Life Stage and Crisis as Predictors of Curiosity and Authenticity: Testing Inferences from Erikson’s Lifespan Theory. International Journal of Behavioral Development, 41, 426-431.
 Maxfield, M., Greenberg, J., Pyszczynski, T., Weise, D.R., Kosloff, S., Soenke, M., Abeyta, A.A and Blatter, J. (2014) Increases in Generative Concern among Older Adults Following Reminders of Mortality. The International Journal of Aging and Human Development, 79, 1-21.
 Ho, M.Y., Cheung, F.M. and Cheung, S.F. (2010) The Role of Meaning in Life and Optimism in Promoting Well-Being. Personality and Individual Differences, 48, 658-663.
 Steger, M.F., Oishi, S. and Kashdan, T.B. (2009) Meaning in Life across the Life Span: Levels and Correlates of Meaning in Life from Emerging Adulthood to Older Adulthood. The Journal of Positive Psychology, 4, 43-52.
 Cornwell, B., Laumann, E.O. and Schumm, L.P. (2008) The Social Connectedness of Older Adults: A National Profile. American Sociological Review, 73, 185-203.
 Seeman, T.E., Lusignolo, T.M., Albert, M. and Berkman, L. (2001) Social Relationships, Social Support, and Patterns of Cognitive Aging in Healthy, High-Functioning Older Adults: MacArthur Studies of Successful Aging. Health Psychology, 20, 243-255.
 Carstensen, L.L., Pasupathi, M., Mayr, U. and Nesselroade, J.R. (2000) Emotional Experience in Everyday Life across the Adult Life Span. Journal of Personality and Social Psychology, 79, 644-655.
 Frijters, P. and Beatton, T. (2012) The Mystery of the U-Shaped Relationship between Happiness and Age. Journal of Economic Behavior Organization, 82, 525-542.
 Hayward, R.D. and Krause, N. (2014) Religion, Mental Health, and Well-Being: Social Aspects. In: Saroglou, V., Ed., Religion, Personality, and Social Behavior, Psychology Press, New York, 255-280.
 George, L.K., Hays, J.C., Flint, E.P. and Meador, K.G. (2004) Religion and Health in Life Course Perspective. In: Schaie, K.W., Krause, N. and Booth, A., Eds., Religious Influences on Health and Well-Being in the Elderly, Springer, New York, 246-282.
 Hayward, R.D. and Elliott, M. (2014) Cross-National Analysis of the Influence of Cultural Norms and Government Restrictions on the Relationship between Religion and Well-Being. Review of Religious Research, 56, 23-43.
 Stavrova, O., Fetchenhauer, D. and Schlosser, T. (2013) Why are Religious People Happy? The Effect of the Social Norm of Religiosity across Countries. Social Science Research, 42, 90-105.
 Hogg, M.A., Adelman, J.R. and Blagg, R.D. (2010) Religion in the Face of Uncertainty: An Uncertainty-Identity Theory Account of Religiousness. Personality and Social Psychology Review, 14, 72-83.
 Krause, N. and Hayward, R.D. (2016) Religion, Health, and Aging. In: George, L.K. and Ferraro, K.F., Eds., Handbook of Aging and the Social Sciences, Academic Press, San Diego, CA, 251-270.
 Ellison, C.G., Burdette, A.M. and Hill, T.D. (2009) Blessed Assurance: Religion, Anxiety, and Tranquility among US Adults. Social Science Research, 38, 656-667.
 Pargament, K.I., Koenig, H.G. and Perez, L.M. (2000) The Many Methods of Religious Coping: Development and Initial Validation of the RCOPE. Journal of Clinical Psychology, 56, 519-543.
 Grefe, D. (2011) Combating Ageism with Narrative and Intergroup Contact: Possibilities of Intergenerational Connections. Pastoral Psychology, 60, 99-105.
 Kessler, E.-M. and Staudinger, U.M. (2007) Intergenerational Potential: Effects of Social Interaction between Older Adults and Adolescents. Psychology and Aging, 22, 690-704.