The world’s population is aging at an unprecedented pace. By 2050, it is estimated that the global number of people aged 65 and older will be more than double, reaching over 1.5 billion individuals (1). The marked increase in the proportion of older people has posed new challenges to public health systems and societies across the globe (2). How to cope with the increasing burden of age-related diseases and conditions has become a point of major concern to health policy makers (3). To address this question, it is not only vital to understand drivers of chronic disease development, but also determinants that ensure overall health and well-being at older age. The concept of successful aging (SA) was introduced by Rowe and Kahn in 1997 to describe the phenomenon of aging in good overall physical, mental, and social wellbeing (4). Originally defined as ‘freedom from disease or disease-disability, high cognitive and physical functioning, and active engagement with life’, the term SA has evolved to include functional ability, independence and quality of life that assure not only living longer but also preserving health and wellbeing until old age (5–7). There has been increasing interest in understanding the role of various exposures throughout the life-course including lifestyle, biological, psychological, and social factors as possible determinants of SA. Several reviews have been previously conducted to evaluate determinants of SA. However, those reviews were focused on specific factors, such as physical activity (8, 9), smoking and alcohol consumption (10), diet (11, 12), and psychosocial factors (13, 14). So far, only one review provided a comprehensive overview of a wider range of determinants including demographic, biological, behavioral, psychological and social factors summarizing evidence published by August 2016 (15). With the continuously increasing interest in the topic, numerous new studies have been published in the recent years. However, the newly emerging evidence has not been summarized yet.

We therefore conducted a systematic review to synthesize the recent evidence from published longitudinal studies on a range of determinants and indicators of SA to identify existing gaps and guide planning of future studies and the development of tailored interventions and policies addressing healthy longevity.

The current review provides a summary of the recent research on determinants of SA, including socio-demographic factors, nutrition, lifestyle, biological pathways, psychological health, and well-being. Overall, a higher socio-economic status, adherence to healthy plant-based diet such as the Mediterranean diet, not smoking, being physically active, and being metabolically healthy, were the factors associated with higher odds for SA. Newly emerging aspects of increasing importance in research on SA include psychological factors and well-being.

The review confirms past research highlighting the value of a healthy lifestyle throughout the life course as a major determinant of SA (32). It essentially points to that adopting an overall healthy lifestyle rather than focusing on avoidance of risk factors seems to be the key to long-term sustained health. These findings largely correspond to the results by previous reviews (8, 15, 42). Among individual determinants, adherence to healthy dietary patterns, such as the Mediterranean diet, have been pronouncedly associated with higher chances for SA (24, 30, 31, 40). In contrast, individual dietary components, such as high carbohydrate intake and high glycaemic index of a diet were not associated with SA (39). The current review found moderation in the consumption of alcohol to be positively associated with SA, albeit in the context of following an overall healthy diet. In contrast, in previous review, Kralj et al. (15) reported mixed findings for the same association. Potential explanations for these discrepant findings could be sought in the assessment and categorization of drinking patterns among studies, the type of alcohol consumed, and the different reference categories used. Our results are in line with results from a more recent systematic review that reported that as compared to complete abstinence moderate alcohol consumption was positively associated with healthy aging (10). Furthermore, our results revealed that sleeping habits including sleeping time and quality were strongly associated with SA (22). This evidence comes in support of previous research showing that sleep is associated with improved cognitive functioning and may be protective against aging-related cognitive decline (43).

Another highlight of the current review is the role of the metabolic health as an important biological intermediate factor for SA (38). Suboptimal levels of lipid metabolism biomarkers, high blood pressure, and high glucose levels over prolonged time periods have been long known to predispose higher risk of age-related chronic diseases, including cardiovascular disease (44) and type 2 diabetes (44), as well as overall mortality, and have also been negatively associated with SA (28). Metabolic disorders are associated with chronic systemic inflammation leading to the generation of reactive oxygen species and oxidative stress that exacerbates the aging process, functional decline, and disease development (45–47). Additional aging phenotypes include the declining functions of the immune system, called immunosenescence, the senescence-associated secretory phenotype, shortened telomeres and decreased telomerase activity. All of these may play an important role as biological determinants for successful aging and further research would be warranted to explore relevant biomarkers associated with these processes individually and conjointly.

Our review further identified an increasing number of studies reporting on psychological factors and well-being in relation to SA. One of these factors reportedly associated with SA was optimism (26, 27). Previous research reported on the inverse association between optimism and chronic disease outcomes, incl. Cardiovascular disease, cancer, mortality, and cognitive decline (48–50). Positive life orientation may affect the adoption and maintenance of behaviors physical activity, less smoking and adherence to a healthy diet (51), which are known risk factors for cardiovascular disease. It is also plausible that optimism and pessimism affect health through biological mechanisms independent of health behaviors. Optimism has been associated with an improved immune response (52), higher levels of antioxidants in the blood (53), and advantageous high density lipoprotein cholesterol levels (54). If confirmed by future research these findings would suggest that the cultivation of optimism may be an important feature of designing strategies promoting SA. In addition, various aspects related to the socio-economic status, such as ethnicity (22, 25), marital status (33), place of residence (25, 33) and debt (25) were also found as determinants of SA. Taken together, our findings go beyond evidence provided by previous reviews, i.e., Kralj et al. (15) by extending the list of socio-economic and cognitive psycho-social factors as determinants of SA. The role of early life health assessment has been also among the newly identified factors reflecting the increased importance in research of understanding life-course determinants of health. This new evidence further underlines the notion that SA, apart from biological and lifestyle aspects, can be strongly influenced by early childhood experiences, mental health and well-being along with social justice and financial inequity.

The evidence of this review originates from well-conducted longitudinal studies, most of which were attributed a low RoB. However, the summary of results is challenging due to several methodological limitations. These include (a) the lack of a standardized definition of successful aging, (b) the large variation of methods employed for the operationalization of its multiple components, and (c) the under-representation of various population groups, particularly from less developed regions and lower socio-economic status. The results from the review should therefore be interpreted considering the differences in both measurement and definition of SA as the outcome of interest. So far, there has not been an accepted universal definition for SA and various operational definitions have been used in research (55). Next to the Rowe and Kahn’s model (4), psychological models of SA have been proposed, such as the concept proposed by Baltes and Baltes (56), which puts more emphasis on the adaptation to the older stages of life and limitations to functional capacity. The model of “Aging well” by Fernandez-Ballesteros et al. (55) further includes activities of daily living, physical and cognitive functioning, social participation and engagement, and positive affect and control as additional domains within the definition of SA. Other researchers such as Young et al. (57, 58) attempted to depict further multidimensional aspects in the definition allowing assessment of SA on a continuous rather than dichotomous scale.

One of the main challenges in conceptualizing SA is combining objective criteria (e.g., functional abilities and the number of chronic conditions) and subjective criteria (e.g., satisfaction with life). To combine information about objective and subjective criteria, Kok et al. (59) quantified SA according to the number of indicators in which individuals showed successful trajectories over the life course. Cosco et al. (60) created the a priori continuous Successful Aging Index using items identified by systematic reviews of operational definitions and lay perspectives of SA which included seven items: maintenance of interest, absence of loneliness, optimism, self-rated health, cognitive functioning, and instrumental activity of daily living. Using confirmatory factor analysis, Kleineidam et al. (61) compared five methods for assessing objective and subjective successful aging (physical health, cognitive health, disability, well-being, and social engagement) and demonstrated that these domains can be combined into a multidimensional construct. Overall, the studies included in the current review predominantly defined SA based on objective measurements of health and functionality and were less focused on a wider range of subjective criteria such as the individuals’ perceptions of their own health and well-being. Recent studies showed that life satisfaction (7), purpose in life (7, 62, 63), and social engagement (14) contributed to SA and therefore should be included in operationalizing SA. Overall, more work is needed on developing a well-constructed definition for SA that balances subjective and objective aspects based on measurements of physiological health, well-being, and social engagement. Future research is warranted to provide agreed-upon operationalization of SA and standardized measurements of its separate components, to facilitate comparable findings and an adequate summary of main tendencies in research.

The strengths of the current systematic review include its actuality based on inclusion of studies published in the past 7 years, thus providing an overview of recent trends and novel findings in research on determinants and indicators of SA. Compared to previous reviews that focused on single factors, this review included a wide range of factors explored as determinants and indicators of SA. The definition of SA was carefully considered and only studies that adhered to the multidimensional concept of SA were included to allow for a better overview on the evolution of its definition and the detection of methodological gaps. The current review was conducted according to the most recent guidelines for conducting and publishing systematic reviews and included a careful assessment of study quality using predefined criteria. Furthermore, only longitudinal studies were included, which allows inferences on temporality of found associations. However, with the observational nature of the studies, causal assumptions cannot be fully supported. Most included studies proved to be of high quality, although some studies were limited by the lack of a proper evaluation of study attrition and insufficient control for potential confounding. Concerning the study attrition, it remains important to report to conduct descriptive analysis on participants that were lost to follow-up, whether they differed from the participants that completed the study, and how the study findings may thus be biased. Future studies should consider methodological limitations and provide sufficient detail on the planning and statistical analysis. The geographical coverage of the current study was also limited, with majority of studies representing populations from Europe, the United States, and Australia. Therefore, current findings may not be generalizable to populations living outside of the global north. Furthermore, the majority of studies were based on older populations which restricted the possibility to explore possible differences in studied exposures according to age group. Future studies including wider age ranges of participants, i.e., representing younger age groups, are warranted to allow a more detailed evaluation of the time and duration of exposure.

Finally, the current review aimed to depict a multidimensional definition of SA, thereby excluding studies that evaluated other age-related outcomes such as disease-free aging or healthy life-expectancy. Despite such outcomes being explored on a wider basis in epidemiology and public health research, they may not sufficiently cover additionally important aspects of the aging concept beyond absence of diseases and disability. Our work and that of previous reviews on SA as a multidimensional outcome underlines the importance of employing a holistic view to define the quality of life at older ages. Understanding the complexity of SA and subsequently fine-tuning novel approaches to address it may hold the key to adding life to years, beyond years to life.

In conclusion, this systematic review provides a summary of the recent evidence on the determinants of successful aging and highlights the importance of healthy living, monitoring metabolic risk along with sustaining mental health and well-being in adult life. Emerging research highlights the role of psycho-social factors and early life health as determinants of SA. Future research is warranted to develop a standardized definition of SA and explore the synergistic effects of its components. Investment in further methodological and research work on SA would pave the way toward development of adequate health promotion policies in aging societies.

The original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author.

CR: Investigation, Writing – original draft, Writing – review & editing. CG: Visualization, Writing – review & editing. RA: Investigation, Writing – review & editing. MB: Writing – review & editing. KA: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing.