What do individual reserves tell us about vulnerable ageing?
Authors: Andreas Ihle, Matthias Kliegel
Journal: The Lancet Healthy Longevity (2021)

The increase in cognitive impairments and physical health constraints observed with our rising life expectancy constitutes one of the biggest challenges for public health in this century.1Suzman R Beard JR Boerma T Chatterji S Health in an ageing world—what do we know?.Lancet. 2015; 385: 484-486Summary Full Text Full Text PDF PubMed Scopus (165) Google Scholar With respect to cognitive health, individuals with greater cognitive and brain reserves have been proposed to be able to maintain cognitive functioning above a clinical threshold for a longer time, although pathology is advancing.2Stern Y An approach to studying the neural correlates of reserve.Brain Imaging Behav. 2017; 11: 410-416Crossref PubMed Scopus (79) Google Scholar, 3Stern Y Cognitive reserve.Neuropsychologia. 2009; 47: 2015-2028Crossref PubMed Scopus (1719) Google Scholar The role of these mechanisms at the later stages of life is not yet clear. Addressing this important question in a prospective cohort study, Jendé Zijlmans and colleagues4Zijlmans JL Lamballais S Lahousse L et al.The interaction of cognitive and brain reserve with frailty in the association with mortality: an observational cohort study.Lancet Healthy Longev. 2021; (published online March 19.)https://doi.org/10.1016/S2666-7568(21)00028-3Summary Full Text Full Text PDF Scopus (1) Google Scholar found that greater cognitive and brain reserves were associated with a lower risk of mortality. Of note, they identified a significant interaction of frailty with cognitive reserve (but not with brain reserve), suggesting that greater cognitive reserve is particularly associated with lower mortality in frail participants. Zijlmans and colleagues highlighted the need to consider the interplay of cognitive reserve and frailty, rather than treating them as independent issues, in order to extend healthy life-years. Thereby, their findings further underline the necessity for a holistic perspective to vulnerable ageing. Recent research on cognitive outcomes has also investigated the interaction of cognitive reserve and frailty.5Ihle A Gouveia ÉR Gouveia BR Orsholits D Oris M Kliegel M Solving the puzzle of cognitive reserve effects on cognitive decline: the importance of considering functional impairment.Dement Geriatr Cogn Disord. 2020; 49: 349-354Crossref PubMed Scopus (1) Google Scholar In general, with greater cognitive reserve, cognitive functioning will begin to decline at a relatively late time, after pathological alterations have accumulated. Yet as soon as cognitive decline begins, the cognitive system collapses rapidly, because pathology has already advanced.3Stern Y Cognitive reserve.Neuropsychologia. 2009; 47: 2015-2028Crossref PubMed Scopus (1719) Google Scholar Frailty might be an indicator or correlate of the ongoing pathology. In this regard, individuals with greater cognitive reserve might be able to maintain cognitive functioning if they still show relatively little functional impairment, because they might still have good overall health, with a cognitive system that is still able to compensate for the ongoing pathology. By contrast, they will suffer from a steeper decline (compared with individuals with less cognitive reserve) as soon as frailty becomes a substantial issue, because frailty might be indicative of pathological changes and the resulting upcoming overall decline at the end of life.5Ihle A Gouveia ÉR Gouveia BR Orsholits D Oris M Kliegel M Solving the puzzle of cognitive reserve effects on cognitive decline: the importance of considering functional impairment.Dement Geriatr Cogn Disord. 2020; 49: 349-354Crossref PubMed Scopus (1) Google Scholar One of the key remaining questions concerns the detailed mechanisms by which cognitive reserve enables individuals with frailty to live longer. Is this finding merely associated with the physiological correlates of pathology and cognitive or physical impairments, or does high cognitive reserve also allow a different behaviour, compensation, or stabilisation (other than preserving cognitive functioning per se)? Are there differences between cognitive and brain reserve in this regard? One avenue to further advance our understanding of these issues is to investigate the availability and activation of cognitive and brain reserves in the particular situations in which the cognitive system is required to adapt. For this purpose, a combination of panel studies and experimentally controlled examinations seems to be a good opportunity for such in-depth analyses. Moreover, the newly developed proxy of cognitive reserve used by Zijlmans and colleagues4Zijlmans JL Lamballais S Lahousse L et al.The interaction of cognitive and brain reserve with frailty in the association with mortality: an observational cohort study.Lancet Healthy Longev. 2021; (published online March 19.)https://doi.org/10.1016/S2666-7568(21)00028-3Summary Full Text Full Text PDF Scopus (1) Google Scholar (estimating cognitive reserve as a function of demographics, brain pathology, and current level of cognition) opens an important discussion because it goes beyond educational attainment, which has been the most frequently used proxy of cognitive reserve to date. We agree that cognitive reserve should be conceptualised and measured as a dynamic construct. Nevertheless, this novel measure includes assessments of current cognitive functioning, potentially creating circular reasoning in studies using cognitive functioning as outcome variables. Therefore, we propose to also investigate lifespan markers of accumulated cognitive reserve (such as occupation and leisure activities), together with cognitive reserve activation. From an overarching perspective, build-up and activation of reserves have been discussed as key mechanisms in the development of both vulnerability and resilience in older age.6Cullati S Kliegel M Widmer E Development of reserves over the life course and onset of vulnerability in later life.Nat Hum Behav. 2018; 2: 551-558Crossref PubMed Scopus (30) Google Scholar In this regard, in contrast to situation-dependent momentary levels of resources, multiple reserves (eg, cognitive, brain, relational) are seen as latent capacities that are needed for protection against damage by delaying or changing the processes of decline in mental and physical health, such as declines that can occur after trauma or adversity.6Cullati S Kliegel M Widmer E Development of reserves over the life course and onset of vulnerability in later life.Nat Hum Behav. 2018; 2: 551-558Crossref PubMed Scopus (30) Google Scholar Importantly, the different reserve domains show joint effects. For example, the combined effects of cognitive reserve and relational reserve (ie, supportive relationships provided by an individual's social network) influence the extent of cognitive decline in old age.7Sauter J Widmer E Baeriswyl M et al.Interactional effects between relational and cognitive reserves on decline in executive functioning.J Gerontol B Psychol Sci Soc Sci. 2020; (published online April 22.)https://doi.org/10.1093/geronb/gbaa054Crossref PubMed Scopus (3) Google Scholar The interaction between cognitive reserve and frailty observed in the study by Zijlmans and colleagues4Zijlmans JL Lamballais S Lahousse L et al.The interaction of cognitive and brain reserve with frailty in the association with mortality: an observational cohort study.Lancet Healthy Longev. 2021; (published online March 19.)https://doi.org/10.1016/S2666-7568(21)00028-3Summary Full Text Full Text PDF Scopus (1) Google Scholar further corroborates the view that a detailed investigation of the interplay of individual reserves and impairments, as well as the dynamics of stressors and momentary resources, within different contexts across the life-course, is needed to better understand the processes of vulnerable ageing.6Cullati S Kliegel M Widmer E Development of reserves over the life course and onset of vulnerability in later life.Nat Hum Behav. 2018; 2: 551-558Crossref PubMed Scopus (30) Google Scholar, 8Spini D Bernardi L Oris M Toward a life course framework for studying vulnerability.Res Hum Dev. 2017; 14: 5-25Crossref Scopus (45) Google Scholar This perspective also calls for interdisciplinarity. For example, a special focus is needed on gender effects. In addition to general sex differences regarding average life expectancy, there are differences between women and men with respect to cognitive reserve build-up in adulthood that might be a result of socialised gender roles.9Ihle A Bavelier D Maurer J Oris M Kliegel M Internet use in old age predicts smaller cognitive decline only in men.Sci Rep. 2020; 108969Crossref PubMed Scopus (11) Google Scholar Moreover, differential patterns exist between women and men regarding predictors of frailty, such as adverse childhood experiences.10Cheval B Chabert C Sieber S et al.Association between adverse childhood experiences and muscle strength in older age.Gerontology. 2019; 65: 474-484Crossref PubMed Scopus (10) Google Scholar Another important factor to consider in more detail is the interplay of reserves built up over the lifespan across different contexts, such as health-care and welfare systems, and across different populations, including the most socially disadvantaged, and taking into account the idiosyncratic life course, personality differences, and subjective attitudes towards ageing. Future research also requires the development and application of innovative operationalisations and methods to study individual reserves. In summary, an overarching perspective guiding interdisciplinary efforts is essential to better understand the mechanisms of individual reserves and their consequences for vulnerable ageing, and to specify practical implications in terms of social policies and individually tailored intervention programmes to support healthy longevity. We declare no competing interests. AI acknowledges support from the Swiss National Science Foundation ( grant number 10001C_189407 ). This work was further supported by the Swiss National Centre of Competence in Research LIVES – Overcoming vulnerability: life course perspectives, granted by the Swiss National Science Foundation ( grant number 51NF40–185901 ). The interaction of cognitive and brain reserve with frailty in the association with mortality: an observational cohort studyHigher cognitive reserve and higher brain reserve were associated with a lower mortality risk. Additionally, cognitive reserve and frailty interact in the association with mortality, such that higher cognitive reserve is particularly associated with lower mortality in frail participants. Full-Text PDF Open Access