Psychosocial and biological pathways to aging

Behavioral and social science is an umbrella term for a variety of disciplines, approaches and methods. Behavioral sciences examine environmental aspects and behavioral, mental, social and physiological processes as well as the interactions of these processes with the social and natural environment, which can be understood as antecedents and consequences of behavior. Disciplines include psychology, anthropology, sociology, economics and cognitive science. Social science focuses more on the study and theorizing of societies and the social exchange processes of individuals within societies. Disciplines include sociology, anthropology, psychology, economics and political science. Behavioral and social gerontology studies how women and men adapt to the environment or shape the environment as they age through the application of behavioral and social theories to aging.

While the geroscience community has long been focused on biological mechanisms in laboratory studies using animal models, the geroscience literature is increasingly opening up to behavioral and social sciences. Behavioral and social science are then described as a “vehicle” for translation from the laboratory to the real-world settings [19]. This approach rarely considers behavioral and social science as equal contributors to the development of interdisciplinary theories of aging. Moffitt argued that geroscience can be “augmented” by behavioral and social sciences to foster the translation from animal models to humans in the living environments. Additionally, the author posited that health inequalities that could otherwise arise from geroscience research can be reduced when knowledge from behavioral and social sciences is considered. Another line of argumentation describes behavioral and social sciences as crucial for information on the design of clinical trials of geroscience interventions and outcomes [19, 21, 23].

Social aging, as opposed to biological aging, has been conceptualized as the aging processes and outcomes that are shaped in their meaning and experiences by societal factors and by the social construction of aging [14]. Behavioral aging refers to aging-related behaviors and their antecedents and outcomes as well as the behavioral interactions between humans and their physical and social environments (for further discussion, see [26]).

A seminal work in social and behavioral aging research recently introduced the social hallmarks of aging [6]. According to Crimmins these social hallmarks are lifetime socioeconomic status, adversity in childhood and adulthood, being a member of a minority group, adverse health behavior and adverse psychological states. Crimmins’ work can be understood as a current push to define the psychosocial conditions of aging and thereby further solidify the relationships to the biological foundations of aging. While it needs to be highlighted that social determinants of individual diseases or healthy aging have been established for decades, the attempt by Crimmins tries to conceptualize the relation of psychosocial factors on the aging process per se. Furthermore, in the theoretical and empirical work of Crimmins, the interrelation of the social hallmarks of aging (i.e., age, gender, socioeconomic status, childhood trauma and health, chronic stressors, depressiveness, negative outlook, and health behavior) with biological mechanisms (i.e., bioage, epigenetic age acceleration, telomere length, mitochondrial DNA copy number) on common outcomes (i.e., instrumental activities of daily living, multimorbidity, cognitive dysfunction, and mortality) was stressed [6]. Recent advances in the availability of high-quality longitudinal panel data containing biological as well as psychosocial variables make the investigation of truly biopsychosocial research on the aging process possible (e.g., Health and Retirement Study [6]).

A recent example where the social and biological hallmarks of aging were combined into a coherent framework is the determinants of multimorbidity in the primer on multimorbidity by Skou et al. [24]. Within this framework, distinct synergistic interplays between both biological and psychosocial factors on multimorbidity were assumed. A third direct interaction with multimorbidity is assumed via the factor “medications”.

The theoretical establishment of an interplay between biological and psychosocial factors is not new. Baltes earlier proposed a meta-theory of aging which outlined the complex interplay of biological and psychosocial factors [1]. The principles of this theory entail a negative age correlation, where genome-based plasticity and biological potential decrease with age. While the biological potential decreases with age, the need for culture-based compensation of biological losses increases. Finally, the efficiency of culture decreases as humans move to very old age.

Another framework was outlined by Kuh et al. [3]. Their integrated life course model of aging combines physiological capacity (e.g., central nervous system integrity, endocrine and immunological system homeostasis, age-related changes in body composition and energy capacity and consumption) emotional health, reproductive health and physical (e.g., material conditions, pollutants, assisted technology) and social environmental factors (e.g., family, neighborhood, retirement, healthcare) and their interaction through specific phases of the life course (i.e., conception, prenatal, prepubertal, pubertal, maturity, senescence).

A fourth well-established framework on the interrelation of biological and psychosocial mechanisms is the biopsychosocial model of the International Classification of Functioning (ICF) of health and illness, which has been used in rehabilitation as well as in geriatrics and related fields. The social and biological models of the ICF are already incorporated within the framework of the comprehensive geriatric assessment for clinical practice.

Figure 1 outlines the theoretical interrelations between biological and psychosocial factors. A first class of models (1 “mediation”) represents a class of models that assumes an indirect effect of psychosocial factors via biological factors on health outcomes. Some models from research on age stereotypes [16, 28] and health and social exchange processes and health [4, 13] belong to this class. Another class of models (2 “moderation”) assumes a connection between biological factors and health, which can, however, be relativized by psychosocial factors. The theory of Baltes belongs to this class [1] as well as the life course model by Ben-Shlomo et al. [3]. A third class of models (3 “interaction”) assumes a dynamic interaction between both biological and psychosocial factors. This class is different from the previous class “moderation” in that an equal interplay of factors is interpreted, while in moderation the path between biology and health or illness is altered by psychosocial factors. The model according to Skou et al. [24] and the ICF model belong to this class. Finally, a fourth class of models (4 “independent”) can be assumed, which assumes the independent or direct effects of both factors, biological and psychosocial. Crimmins’ analyses [6] belong to this class, which can also be understood as a precursor to model class 1.

While fully interdisciplinary aging research is still scarce, examples of established biopsychosocial aging research exist. The biopsychosocial model of disease stresses the interconnectedness between biological, psychological and social factors in determining an individual’s medical condition. The interplay between the three factors determines the cause, manifestation and resolution of disease, emphasizing complex dynamics beyond biological factors. Aging research should therefore consider social and behavioral factors alongside biological factors to deal with the disruptive effects of the aging process. Complex pathways of psychosocial concepts on health are described and empirically tested, for instance, in the field of views on aging and health as well as relationship quality in health and aging.

Geroscience formulates a vision for preventing age-related diseases and loss of function by targeting biological mechanisms of aging [21]. There is a critical debate in social gerontology regarding the geroscience perspective on the aging process, but also on the need for incorporation of senescence into social science and social gerontology [8, 9]. Gilleard and Higgs, for instance, argued that recognizing the social structuring of later life is important to understand aging beyond “aging as senescence” including positive views on aging, benefits and gains for the aged person, the community and the society [9]. Social gerontology can critically capture concerns with anti-aging and longevity extension scenarios that have been raised by geroscience scholars. Conversely, ignoring senescence in social gerontology risks not comprehensively understanding aging in its interdependence of “ageing bodies, ageing subjects and ageing societies” [9].

The aforementioned “vehicle” approach to use the findings of behavioral science as a method to ensure adherence and to initiate behavior in geroscience attempts, so to speak as a methodological tool, without these sciences themselves being part of the theory-testing or generating scientific process, must certainly be critically questioned. Research on an equal level between disciplinary perspectives would certainly be a much more fruitful approach. This approach would involve developing and testing both behavioral and geroscience theories at the same time or, in the best-case scenario, establishing even a truly interdisciplinary theory that integrates both perspectives into one approach.

This article briefly outlines existing research on behavior, inequality, social exchange, and views on aging in relation to the research on biology of aging; however, there are many more emerging fields of interaction that could not be touched on in the article. For instance, the lifespan theory by Carstensen et al. (e.g., [5]), but also established concepts such as loneliness [15], cognition, stress appraisal, and controls beliefs and their links to biogerontology are not discussed here for reasons of space limitations. Additionally, the rapidly expanding field of sociogenomics is likely to advance the inclusion of social factors into biological aging research by untangling complex interactions between inherent genetic susceptibility and social environmental exposures [31]. Finally, trends in population aging led to the emergence of biodemography, a promising field that revealed new insights into the nature of human longevity, including postponement of mortality and senescence, healthy life span and demography of healthy aging [32].

There are methodological advances in social and behavioral gerontology such as MAIHDA and EMA as mentioned before, which could incorporated into an interdisciplinary research agenda. Another important discussion refers to data infrastructures that enable this interdisciplinary work between behavioral and social gerontology and biogerontology. Concerning longitudinal and representative data, the health and retirement study is currently among the rare exceptions.

A joint research agenda that integrates all disciplinary approaches on an equal footing is necessary in order to successfully pursue this interdisciplinary endeavor of combining social and behavioral research with the biology of aging to answer the complex questions that concern our societies. The question remains, what can one perspective do better than the other and where synergies can best arise. This work provides examples of fruitful approaches and provides empirical examples but also shows the limitations.

The discussion should certainly be based on the negotiation of central terminologies as to what is understood as “normal aging” and what is understood as “pathological aging” or what can be understood as health and illness. The integration of social and behavioral science thinking with geroscience could also mean first agreeing on common questions that are of interest in aging: These could be the life span approach, conception of resilience and prevention, or understanding diversity, understanding plasticity and understanding the multidimensionality of any development or prediction of healthy life span or mortality. In this respect, the boundaries between social and behavioral science and geroscience seem to have to been overcome before cooperation with the same view on the aging process and a common view what constitutes a human is possible. In this respect, it has to be kept in mind that geroscience is not the same as biogerontology or biology of aging and objecting to one does not necessarily mean criticizing the other.

In this article a taxonomy of interdisciplinary models is proposed (see Fig. 1). This may structure existing theoretical and empirical work in gerontology and guide future attempts to work across disciplinary borders. Being clear about the nature or relation of the combination of constructs of models from different disciplines is the key to further joint research.