Ivan BautmanspersName, Veerle KnooppersName, Jotheeswaran Amuthavalli ThiyagarajanpersName, Andrea B MaierpersName, John R BeardpersName, Ellen FreibergerpersName, Daniel BelskypersName, Mylene Aubertin-LeheudrepersName, Christopher MiktonpersName, Matteo CesaripersName, Yuka SumipersName, Theresa DiazpersName, Anshu BanerjeepersName (2022date). “WHO working definition of vitality capacity for healthy longevity monitoring..” The Lancet Healthy Longevitytitle·j.
Object of study — the concept of vitality capacityterm·dom within WHO's intrinsic capacityterm·dom framework
Research question — what the attributes of vitality capacityterm·dom are and how it should be defined
Contribution — a consensual working definition of vitality capacityterm·dom and a shortlist of candidate biomarkersterm·key
phenomenon · claim-type · cross-domain-transfer · mechanism · claim-relation · replication-status · limitation — grounded in the full text| phenomenon | confusing use of the term vitality for lack of an operational definition — “The absence of an operational definition results in confusing use of the term in the literature and in a lack of clarity on the measurement tools that might be used to capture or quantify vitality.” | |
| claim-type | existence — “However, no consensual, operational definition of vitality capacity has been proposed in the literature so far.” | |
| method — evidence | — “The meeting was held virtually on Dec 8–9, 2021, gathering WHO staff members and 20 experts ( appendix p 2 ) representing six WHO regions.” | |
| object of study — evidence | — “To advance the measurement and monitoring of vitality capacity, the WHO Ageing and Health Unit and the Frailty in Ageing research group at the Vrije Universiteit Brussel (Brussels, Belgium), organised a working group meeting to discuss and clarify the attributes of vitality capacity and to develop a clear conceptual working definition of the term.” | |
| research question — evidence | — “The aims of the meeting were to review the conceptual framework for vitality capacity in people aged 60 years and older, discuss the attributes of vitality capacity, and develop a working definition of vitality capacity.” | |
| contribution — evidence | — “Potential biomarkers to measure vitality capacity were identified, and the following consensual working definition was developed: vitality capacity is a physiological state (due to normal or accelerated biological ageing processes) resulting from the interaction between multiple physiological systems, reflected in (the level of) energy and metabolism, neuromuscular function, and immune and stress response functions of the body.” | |
| mechanism | mitochondria Energy available for daily functioning depends on mitochondrial function, which itself ages, together with nutritional intake. — “At the cellular level, energy availability is highly dependent on the function of mitochondria, which are also subject to the ageing process and together with nutritional intake, determine the total energy an individual can use in daily functioning.” | mechanisms[0] |
| sense | vitality (earliest usage) - the body functions that turn dietary intake into the energy needed for homoeostasis — “The term vitality was first used to describe the body functions devoted to metabolising dietary intakes to produce the required amount of energy for the maintenance of optimal homoeostasis.” | senses[0] |
| sense | vitality (later usage) - a person's biophysiological status and capacity to keep homoeostasis under ordinary and unexpected challenges — “The term was subsequently used to describe the biophysiological status of an individual and the capacity for maintaining homoeostasis in the face of usual daily exposures and of more extreme and unusual or unexpected challenges, such as injury or infection.” | senses[1] |
| relation | chronic low-grade inflammatory profile —same-as→ inflammageing — In immune and stress response, ageing has been shown to be accompanied by a chronic low-grade inflammatory profile, also known as inflammageing. — “In immune and stress response, ageing has been shown to be accompanied by a chronic low-grade inflammatory profile, also known as inflammageing.” | concept_edges[0] |
| weight | chronic low-grade inflammatory profile —same-as→ inflammageing — 0.9 — “In immune and stress response, ageing has been shown to be accompanied by a chronic low-grade inflammatory profile, also known as inflammageing.” | concept_edges[0] |
| relation | frailty —contrasted-with→ vitality capacity — Whereas frailty is a rather static approach of evaluating reserve capacity, vitality capacity can be conceptualised as a continuum measure across the lifespan of older adults. — “Whereas frailty is a rather static approach of evaluating reserve capacity, vitality capacity can be conceptualised as a continuum measure across the lifespan of older adults.” | concept_edges[1] |
| weight | frailty —contrasted-with→ vitality capacity — 0.8 — “Whereas frailty is a rather static approach of evaluating reserve capacity, vitality capacity can be conceptualised as a continuum measure across the lifespan of older adults.” | concept_edges[1] |
| effect direction | decline in homoeostatic reserves —causes→ resistance to stressors — reduces — “Although the debate regarding the conceptual definition of frailty is ongoing, researchers generally agree that frailty is a dynamic, age-related condition characterised by a decline in homoeostatic reserves in multiple physiological systems, which leads to decreased resistance to stressors and increased risk of adverse health outcomes, such as falls, hospitalisation, diminished mobility, increasing disability in activities of daily living and, ultimately, premature death.” | concept_edges[2] |
| relation | decline in homoeostatic reserves —causes→ resistance to stressors — Although the debate regarding the conceptual definition of frailty is ongoing, researchers generally agree that frailty is a dynamic, age-related condition characterised by a decline in homoeostatic reserves in multiple physiological systems, which leads to decreased resistance to stressors and increased risk of adverse health outcomes, such as falls, hospitalisation, diminished mobility, increasing disability in activities of daily living and, ultimately, premature death. — “Although the debate regarding the conceptual definition of frailty is ongoing, researchers generally agree that frailty is a dynamic, age-related condition characterised by a decline in homoeostatic reserves in multiple physiological systems, which leads to decreased resistance to stressors and increased risk of adverse health outcomes, such as falls, hospitalisation, diminished mobility, increasing disability in activities of daily living and, ultimately, premature death.” | concept_edges[2] |
| weight | decline in homoeostatic reserves —causes→ resistance to stressors — 0.75 — “Although the debate regarding the conceptual definition of frailty is ongoing, researchers generally agree that frailty is a dynamic, age-related condition characterised by a decline in homoeostatic reserves in multiple physiological systems, which leads to decreased resistance to stressors and increased risk of adverse health outcomes, such as falls, hospitalisation, diminished mobility, increasing disability in activities of daily living and, ultimately, premature death.” | concept_edges[2] |
| replication | not-applicable | |
| limitation | No consensus was reached on attributes such as nutrition, which some experts treated as a determinant and others as an outcome of vitality. — “Consensus was not reached during the meeting on other possible attributes, such as nutrition, because some of the experts considered it to be a determinant of vitality whereas others considered it an outcome of vitality.” | limitations[0] |
| limitation | The definition is conceptual; an operational definition still requires a systematic review of candidate biomarkers. — “The next step is to perform a systematic review of the potential biomarkers (blood-based, physical, and self-reported biomarkers) of vitality capacity to develop an operational definition of vitality capacity that allows its systematic measurement and monitoring.” | limitations[1] |
finding · quantity · variable · definition · key-term — grounded in the full text| finding | Grip strength, as a measure of neuromuscular function, predicts disability, falls and mortality in community-dwelling older adults. — “For instance, neuromuscular function, which can be easily quantified by grip strength using a hand-held dynamometer device, 32 has been suggested as a biomarker of ageing and seems to be a strong predictor for disability (odds ratio [OR] 1·78 [95% CI 1·28–2·48]), falls (1·15 [1·01–1·33]), and mortality (1·79 [1·26–2·55]) in community-dwelling older adults.” | content_tags.findings[0] |
| quantity | twenty experts — — “To advance the measurement and monitoring of vitality capacity, a working group of WHO staff members and twenty experts representing six WHO regions was convened to discuss and clarify the attributes of vitality capacity and to develop a clear working definition of the concept.” | content_tags.quantities[0] |
| key-terms | vitality capacity, intrinsic capacity, healthy ageing, functional ability, frailty, biomarkers, inflammageing, handgrip strength, fatigue, biological ageing |
| concept | intrinsic capacity — the composite of all the physical and mental capacities that an individual can draw on — “Intrinsic capacity, a crucial concept in healthy ageing, is defined by WHO as “the composite of all the physical and mental capacities that an individual can draw on at any point in time”. Vitality capacity is considered the underlying physiological determinant of intrinsic capacity.” | concepts[0] |
| concept | vitality capacity — a physiological state (due to normal or accelerated biological ageing processes) resulting from the interaction between multiple physiological systems, reflected in (the level of) energy and metabolism, neuromuscular function, and immune and stress response functions of the body — “To conclude, the following consensual working definition was developed: vitality capacity is a physiological state (due to normal or accelerated biological ageing processes) resulting from the interaction between multiple physiological systems, reflected in (the level of) energy and metabolism, neuromuscular function, and immune and stress response functions of the body.” | concepts[1] |
| concept | Healthy ageing — the process of developing and maintaining the functional ability that enables well-being in older age — “Healthy ageing is defined by WHO as “the process of developing and maintaining the functional ability that enables well-being in older age”.” | concepts[2] |
| concept | Functional ability — all the health-related attributes that enable people to be and to do what they have reason to value — “Functional ability is then introduced as “all the health-related attributes that enable people to be and to do what they have reason to value”.” | concepts[3] |
| concept | frailty — a clinical condition characterized by the individual's increased vulnerability to endogenous and exogenous stressors — “Frailty is one of the most prominent barriers to healthy ageing and is conceptually defined as “a clinical condition characterized by the individual's increased vulnerability to endogenous and exogenous stressors” by the consensus opinions of experts involved in the Frailty Consensus Conference.” | concepts[4] |
| concept | chronic low-grade inflammatory profile — not defined in this paper's own words; persistent mild inflammation that accompanies ageing — “In immune and stress response, ageing has been shown to be accompanied by a chronic low-grade inflammatory profile, also known as inflammageing.” | concepts[5] |
| concept | inflammageing — a chronic low-grade inflammatory profile — “In immune and stress response, ageing has been shown to be accompanied by a chronic low-grade inflammatory profile, also known as inflammageing.” | concepts[6] |
| concept | decline in homoeostatic reserves — not defined in this paper's own words; loss of the body's spare physiological capacity across systems — “Although the debate regarding the conceptual definition of frailty is ongoing, researchers generally agree that frailty is a dynamic, age-related condition characterised by a decline in homoeostatic reserves in multiple physiological systems, which leads to decreased resistance to stressors and increased risk of adverse health outcomes, such as falls, hospitalisation, diminished mobility, increasing disability in activities of daily living and, ultimately, premature death.” | concepts[7] |
| concept | resistance to stressors — not defined in this paper's own words; the ability to withstand internal and external challenges to health — “Although the debate regarding the conceptual definition of frailty is ongoing, researchers generally agree that frailty is a dynamic, age-related condition characterised by a decline in homoeostatic reserves in multiple physiological systems, which leads to decreased resistance to stressors and increased risk of adverse health outcomes, such as falls, hospitalisation, diminished mobility, increasing disability in activities of daily living and, ultimately, premature death.” | concepts[8] |
Full text — tagged
WHO working definition of vitality capacityterm·dom for healthy longevity monitoring.
Abstract Intrinsic capacityterm·dom, a crucial concept in healthy ageingterm·dom, is defined by WHO as “the composite of all the physical and mental capacities that an individual can draw on at any point in time”. Vitality capacityterm·dom is considered the underlying physiological determinant of intrinsic capacityterm·dom. To advance the measurement and monitoring of vitality capacityterm·dom, a working group of WHO staff members and twenty experts representing six WHO regions was convened to discuss and clarify the attributes of vitality capacityterm·dom and to develop a clear working definition of the concept. Potential biomarkersterm·key to measure vitality capacityterm·dom were identified, and the following consensual working definition was developed: vitality capacityterm·dom is a physiological state (due to normal or accelerated biological ageingterm·key processes) resulting from the interaction between multiple physiological systems, reflected in (the level of) energy and metabolism, neuromuscular function, and immune and stress response functions of the body.
Introduction Population ageing is a major demographic transition that presents both opportunities and challenges. From 2000 to 2050, the proportion of the world's population aged 60 years and older will double, whereas the proportion of those aged 80 years and older will almost quadruple. 1 Although this demographic change is, on the one hand, a triumph of health care and socioeconomic development, on the other hand it poses major challenges for societies because longer lives come with drawbacks. Additionally, important inequalities in life expectancy persist across and within continents and countries. 2 Healthy longevity depends on policies, health-care systems, and different health determinants. 3 Therefore, ageing is not identical in each country, which further compounds the heterogeneity in longevity between different regions or countries.
WHO advocates moving away from a disease-focused model of ageing and frailtyterm·dom, and towards a more positive model of healthy ageingterm·dom that focuses on preserving functional abilityterm·dom and preventing loss of capacity. Healthy ageingterm·dom is defined by WHO as “the process of developing and maintaining the functional abilityterm·dom that enables well-being in older age”. 1 Functional abilityterm·dom is then introduced as “all the health-related attributes that enable people to be and to do what they have reason to value”. 1 Intrinsic capacityterm·dom is defined by WHO as “the composite of all the physical and mental capacities that an individual can draw on” at any point in time. 1 Functional abilityterm·dom is determined by intrinsic capacityterm·dom, but also by environmental factors and by the interactions between them.
Although various domains of intrinsic capacityterm·dom next to vitality have been proposed (ie, locomotion and psychosocial, sensory, and cognitive 4 , 5 ), no current consensus exists on what such a construct might be composed of, and few metrics have been identified for systematic quantification or monitoring of intrinsic capacityterm·dom. Most domains of capacity are overt and readily amenable to assessment. Vitality capacityterm·dom has been suggested as a core domain, representing the underlying physiological component of intrinsic capacityterm·dom. 6 , 7 However, a definition of vitality capacityterm·dom is still under debate by WHO and others. The term vitality was first used to describe the body functions devoted to metabolising dietary intakes to produce the required amount of energy for the maintenance of optimal homoeostasis. 4 , 8 The term was subsequently used to describe the biophysiological status of an individual and the capacity for maintaining homoeostasis in the face of usual daily exposures and of more extreme and unusual or unexpected challenges, such as injury or infection. 9 Vitality might thus be conceptualised as the amount of intrinsic capacityterm·dom that can be retained, and could be seen as underlying an individual's vigour, stamina, and resilience to challenges. 10 However, no consensual, operational definition of vitality capacityterm·dom has been proposed in the literature so far. The absence of an operational definition results in confusing use of the term in the literature and in a lack of clarity on the measurement tools that might be used to capture or quantify vitality.
If vitality capacityterm·dom is being considered as the underlying physiological determinant of intrinsic capacityterm·dom, early detection of deterioration might allow for early interventions to preserve or increase intrinsic capacityterm·dom. This preservation of intrinsic capacityterm·dom would enable older people to do “what they have reason to value” and to be active and functional in the society in which they live. Three main characteristics for vitality were proposed by CesaripersName and colleagues 4 in a framework for intrinsic capacityterm·dom: hormonal function, energy metabolism, and cardiorespiratory function. Other attributes such as nutrition, body composition, depression status, respiratory function, muscle endurance, and subjective vitality scales are also proposed in the literature for assessing vitality capacityterm·dom in older people. 4 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 A growing body of evidence from the field of geroscience describes in many ways similar underlying physiological attributes, such acellular senescence, DNA integrity, and intercellular communication. 7 , 20 Ageing is accompanied by physical and functional deterioration and by reduction of homoeostatic reserves in multiple physiological systems, leading to a decreased resistance to stressorsterm and to an increased risk of adverse health outcomes—a state called frailtyterm·dom. 18 , 21 Frailtyterm·dom is one of the most prominent barriers to healthy ageingterm·dom and is conceptually defined as “a clinical condition characterized by the individual's increased vulnerability to endogenous and exogenous stressors” by the consensus opinions of experts involved in the Frailtyterm·dom Consensus Conference. 22 Frailtyterm·dom represents a state of vulnerability to stressors defined by a clinical reduction of reserves, and reduced vitality could be one of the factors leading to frailtyterm·dom ( panel 1 ). Frailtyterm·dom is generally described as a phenotype characterised by a decline of functional and clinical characteristics below a particular threshold (eg, in the Fried Frailtyterm·dom Index 25 ), or showing an accumulation of deficits (eg, in the Rockwood Frailtyterm·dom Index 26 ). Frailtyterm·dom is integrated in the life course, and frail older adults have a higher risk of decline than robust older adults, leading to an increased risk of adverse outcomes. However, vitality capacityterm·dom describes continuums that theoretically extend across the life course and that can also evaluate positively. Therefore, Belloni and CesaripersName 8 proposed that frailtyterm·dom is a state of deficit accumulation with ageing across the life course. When the available physiological reserves are too low, a person might not be able to cope with any stressor, explaining the trajectory from the pre-frailty state to the frailtyterm·dom state. By evaluating vitality capacityterm·dom, the functional and physiological reserves of a person can be evaluated. Therefore, vitality capacityterm·dom and frailtyterm·dom can be seen as related but opposite sides of the spectrum. 8 Although the debate regarding the conceptual definition of frailtyterm·dom is ongoing, researchers generally agree that frailtyterm·dom is a dynamic, age-related condition characterised by a decline in homoeostatic reservesterm in multiple physiological systems, which leads to decreased resistance to stressorsterm and increased risk of adverse health outcomes, such as falls, hospitalisation, diminished mobility, increasing disability in activities of daily living and, ultimately, premature death. 23 , 24 Despite this heterogeneity, operational frailtyterm·dom scales can be broadly categorised into three main models: frailtyterm·dom instruments measuring physical frailtyterm·dom (based primarily on physical deficits); multidomain frailtyterm·dom instruments (based primarily on a combination of psychological, cognitive, functional, and social deficits); and indexes of accumulated deficits. 24 Frailtyterm·dom represents a state of susceptibility to stressors defined by a clinical reduction of homoeostatic reserves, and reduced vitality is one of the factors leading to frailtyterm·dom. When vitality represents the reserves of an individual with dynamic trajectories, frailtyterm·dom can be defined as a state of deficit accumulation caused by ageing. 8 Measuring vitality in the concept of frailtyterm·dom can benefit health-care professionals because it can inform when to take action to reverse the trend towards frailtyterm·dom. Measuring can corroborate clinical decisions by providing objective data that will go beyond the traditional view on frailtyterm·dom; vitality can therefore give an overview of the biological reserves of an individual. Therefore, these two concepts can be seen as complementary; a reduction in vitality can lead to a state of susceptibility to stressors (frailtyterm·dom).
Although several ideas converge on the structure of intrinsic capacityterm·dom and its subdomains, a clear and consensual working definition of vitality capacityterm·dom is still lacking. To move towards a positive model of healthy ageingterm·dom and a focus on preserving functional abilityterm·dom, defining a consensus definition of vitality capacityterm·dom and its measurements is vital. Therefore, the WHO Ageing and Health Unit, part of the Department of Maternal, Newborn, Child and Adolescent Health and Ageing (Geneva, Switzerland), proposed to bring opinion leaders together in an expert meeting to discuss the operational definition of vitality capacityterm·dom.
Expert meeting report Purpose To advance the measurement and monitoring of vitality capacityterm·dom, the WHO Ageing and Health Unit and the Frailtyterm·dom in Ageing research group at the Vrije Universiteit Brussel (Brussels, Belgium), organised a working group meeting to discuss and clarify the attributes of vitality capacityterm·dom and to develop a clear conceptual working definition of the term. The meeting was held virtually on Dec 8–9, 2021, gathering WHO staff members and 20 experts ( appendix p 2 ) representing six WHO regions. The aims of the meeting were to review the conceptual framework for vitality capacityterm·dom in people aged 60 years and older, discuss the attributes of vitality capacityterm·dom, and develop a working definition of vitality capacityterm·dom. As a next step, the proposed working definition and the identified attributes for vitality capacityterm·dom will be used as a reference to conduct a systematic review of the literature on measures that can be recommended for routine monitoring of vitality capacityterm·dom, which use, for example, data from health information systems and population surveys.
Methods During the meeting, presentations on the meeting objectives and background information were given by members of WHO and the Vrije Universiteit Brussel to pave the way for the discussions ( appendix p 3 ). These presentations included the WHO public health framework for healthy ageingterm·dom, a clinical perspective of vitality capacityterm·dom, and outcomes of a focused overview of the concepts and attributes of vitality capacityterm·dom ( appendix pp 4–7 ). This focused overview of the existing concepts and definitions of vitality capacityterm·dom started from definitions that already exist in the literature, to select existing definitions and proposed attributes of vitality capacityterm·dom. On the basis of these concepts, a new conceptional definition of vitality capacityterm·dom could be created, taking into account the concepts that have been published in the literature. A discussion took place on the diagram of vitality developed by BeardpersName and colleagues 7 ( figure ). In this diagram, three different levels of vitality capacityterm·dom are proposed, starting at genetic inheritance, followed by biomolecular systems affected by biological ageingterm·key (eg, cellular senescence, glycation, and low-grade inflammation), and higher level physiological systems (including energy homoeostasis, stress response systems, and repair mechanisms). The rate of biological ageingterm·key will determine the intervariability in vitality capacityterm·dom in ageing individuals. In this approach, the three levels are inter-related, which means that the higher level physiological systems are determined by genetic inheritance and biomolecular systems. The experts advised to adapt this model by distinguishing predictors and outcomes of vitality capacityterm·dom, and to focus on the higher level physiological systems when elaborating a consensus-based working definition. During a virtual brainstorming session, the experts were asked to indicate all potentially relevant attributes of vitality capacityterm·dom that are related to higher level physiological systems. The large set of attributes were evaluated and grouped under the labels of energy level, fatigueterm·key, metabolism, strength, respiratory function, body composition, cardiovascular function, nutrition, and immune system response; several other attributes could not be clustered ( panel 2 , part A). Several physical tests such as gait speed or sit-to-stand tests were also proposed; however, these tests were not retained because they belong to locomotor capacity, which is another domain of intrinsic capacityterm·dom. By trying to understand the retrieved attributes and to relate them to higher level physiological systems, three constructs of vitality capacityterm·dom were proposed: neuromuscular function, energy and metabolism, and immune and stress response functions.
Framework of intrinsic capacityterm·dom discussed during the expert meeting SASP=senescence-associated secretory phenotype. Reproduced from BeardpersName et al, 7 by permission of Oxford University Press.
Part A: Potentially relevant attributes of vitality capacityterm·dom related to higher level physiological systems Strength and respiratory function • Respiratory muscle strength • Handgrip strengthterm·key • Respiratory rate at rest and during exercise The level of energy of a person • Energy level • Energy balance • Energy metabolism • Energy expenditure Fatigueterm·key • Fatigueterm·key symptoms • Fatiguability • Muscle endurance • Daytime fatigueterm·key • Self-perceived fatigueterm·key Metabolism • Insulin sensitivity • Haemoglobin • Glycated haemoglobin (HbA 1c ) • Serum albumin • Fasting blood glucose • Hypothalamic–pituitary–adrenal axis hormonal status Body composition • Anthropometry • Bodyweight • BMI • Waist circumference • Muscle mass Cardiovascular function • Heart rate during and after physical activity • Heart rate variability • Oxygen saturation • Orthostatic hypotension • Orthostatic response after recumbency • Blood pressure • Cardiovascular system health • Maximum oxygen consumption Nutrition • Nutritional status (Mini Nutritional Assessment) • Undernutrition • Malnutrition • Weight loss • Loss of appetite Others • Sympathetic and parasympathetic nervous system function • Low self-esteem • Mitochondrial function • Sedentary behaviour • Sleep quality • Methylation clock • Electrolyte balance Part B: Consensus on the top candidate attributes for vitality capacityterm·dom Energy and metabolism • Self-perceived fatigueterm·key • Muscle endurance • Malnutrition or nutritional status • Body composition • Circulating biomarkersterm·key of metabolism (eg, HbA 1c ) Neuromuscular function • Knee extensor strength • Handgrip strengthterm·key • Respiratory muscle strength Immune and stress response • Circulating biomarkersterm·key of inflammation • Perceived immune status (ie, measured by immune status questionnaire) • Oxygen saturation • Autonomic function Next, experts were divided in three breakout rooms, where they were asked to indicate the top three potential biomarkersterm·key for each of these three major constructs of vitality capacityterm·dom. These biomarkersterm·key needed to fulfil the following criteria: feasible to quantify biomarkersterm·key or proxy biomarkersterm·key; feasible to measure or collect in low-resource settings; useful and informative for monitoring (sufficient sensitivity to change with intervention); distinctiveness (ie, no overlap with other attributes of vitality capacityterm·dom); acceptable cost and resource demand; sufficient availability and no ethical concerns in collecting and reporting data; and implementable (eg, in dedicated population surveys on ageing or multipurpose surveys; table ). These criteria imply that vitality capacityterm·dom is a dynamic process and, therefore, the selected biomarkersterm·key need to be able to detect changes over time. Discussions within these breakout rooms resulted in the identification of several markers: strength (eg, handgrip strengthterm·key); energy and metabolism markers (eg, albumin and glycated haemoglobin [HbA 1c ] concentrations, malnutrition, waist or calf circumference, fatigueterm·key, BMI, inflammation, and haemoglobin concentration); and inflammation and stress response (eg, C-reactive protein concentration, perceived immune status [eg, measured by immune status questionnaire 27 ], self-reported immune status, oxygen saturation in combination with strength tests, orthostatic hypotension, and heart rate variability). To reach consensus, we did another virtual exercise during which each expert had to propose their top two candidate markers for neuromuscular function, energy and metabolism function, and immune and stress response function. Discussions following the merging of the breakout rooms resulted in the identification of the biomarkersterm·key shortlisted in panel 2 , part B.
Attributes and criteria applied to potential biomarkersterm·key of vitality capacityterm·dom Consensus was not reached during the meeting on other possible attributes, such as nutrition, because some of the experts considered it to be a determinant of vitality whereas others considered it an outcome of vitality. Finally, nutrition was included in the vitality framework as the capacity of the body to convert food into nutrients to produce energy, and thus categorised under the energy and metabolism domain.
Proposed working definition of vitality capacityterm·dom To conclude, the following consensual working definition was developed: vitality capacityterm·dom is a physiological state (due to normal or accelerated biological ageingterm·key processes) resulting from the interaction between multiple physiological systems, reflected in (the level of) energy and metabolism, neuromuscular function, and immune and stress response functions of the body.
Discussion The current model of health care is designed to anticipate or react to a disease when it manifests clinically, ensuing in medical treatment to eliminate or limit the consequences of the disease. By contrast, the WHO model of intrinsic capacityterm·dom allows for the identification of people in the community that show either stable or reduced intrinsic capacityterm·dom, and of those with reduced intrinsic capacityterm·dom at an early stage, at which point it might be feasible to deliver interventions to prevent further decline and functional losses. Measuring vitality capacityterm·dom as one of the components of intrinsic capacityterm·dom can facilitate the monitoring of health trajectories along the life course and across multiple care settings.
Observing the trend in vitality capacityterm·dom over time (eg, for a whole country) can be informative because these observations can provide information on the factors influencing biological age. Biological ageingterm·key reflects the accumulation of damage and compensation for different hallmarks of ageing, 28 rather than functional limitations. 29 Cellular and intercellular measures of biological age have been validated against chronological age, and measurements of vitality capacityterm·dom could thus help to predict an individual's vulnerability to adverse health outcomes on the basis of their level of reserves and functioning rather than their chronological age. 30 , 31 Changes over time in vitality capacityterm·dom might be related to biological ageingterm·key, and biomolecular systems are one of the underlying processes that will determine the level of vitality capacityterm·dom. Interest in the vitality domain of intrinsic capacityterm·dom is increasing, and debate has been ongoing on whether vitality capacityterm·dom could be a proper condition for intrinsic capacityterm·dom, rather than a separate domain. Early detection of deterioration could thus lead to interventions to preserve or increase intrinsic capacityterm·dom in older people. Several elements in the literature were considered for a new proposed working definition of vitality capacityterm·dom that could also be linked to healthy longevity. For instance, neuromuscular function, which can be easily quantified by grip strength using a hand-held dynamometer device, 32 has been suggested as a biomarkerterm·key of ageing and seems to be a strong predictor for disability (odds ratio [OR] 1·78 [95% CI 1·28–2·48]), falls (1·15 [1·01–1·33]), and mortality (1·79 [1·26–2·55]) in community-dwelling older adults. 33 , 34 , 35 , 36 In immune and stress response, ageing has been shown to be accompanied by a chronic low-grade inflammatory profileterm, also known as inflammageingterm·dom. 37 Chronic low-grade inflammation is a key element of accelerated biological ageingterm·key and of the pathophysiology of frailtyterm·dom and sarcopenia. 19 , 38 , 39 Fatigueterm·key is included in the domain of energy and metabolism, and characterises the depletion of physiological reserve capacity 40 leading to an increased risk of negative health outcomes, such as mortality. 41 Fatigueterm·key has also been shown to be a predictor of several negative health outcomes, such as mortality (OR 2·29 [95% CI 1·67–3·14]), physical disabilities (3·70 [2·80–4·87]), hospitalisation (hazard ratio 1·74 [1·48–2·05]), and physical decline (1.41 (1·28–1·56]) in community-dwelling older adults. 41 Another study showed that the combination of high self-perceived fatigueterm·key and low muscle endurance was associated with a higher risk for frailtyterm·dom. 17 At the cellular level, energy availability is highly dependent on the function of mitochondria, which are also subject to the ageing process and together with nutritional intake, determine the total energy an individual can use in daily functioning. 42 Albumin is a marker for nutritional status, and low albumin concentration is a predictor for mortality (with ORs ranging from 7·5 to 12·5). 43 Although some of the measures of vitality are directly related to biological ageingterm·key, others are proxy measures. However, all these markers of vitality capacityterm·dom reflect biological ageingterm·key, which can be accelerated by behavioural and environmental factors. 44 Vitality capacityterm·dom is being considered as the underlying physiological determinant of intrinsic capacityterm·dom and is therefore related to the other domains of intrinsic capacityterm·dom ( figure ). The new working definition of vitality capacityterm·dom and the proposed attributes can consequently influence other intrinsic capacityterm·dom domains. For example, glycans, such as prolonged concentrations of HbA, are a key factor in neuropathy. 45 Higher concentrations of HbA 1c are also seen in people with diabetes or prediabetes, and this attribute of vitality capacityterm·dom could thus be related to the sensory domain of intrinsic capacityterm·dom. The ability to move from one place to another is part of locomotor capacity; 46 however, sufficient muscular strength is necessary to complete functional tasks (eg, rising from a chair) and is also related to neuromuscular function, which is part of vitality capacityterm·dom. These examples illustrate how vitality capacityterm·dom can influence the other domains of intrinsic capacityterm·dom.
Vitality in the context of frailtyterm·dom can corroborate clinical decisions with objective data that will go beyond the traditional view on frailtyterm·dom. Whereas frailtyterm·dom is based on the accumulation of deficits with ageing, vitality has a more positive approach that advocates moving away from a disease-focused model of ageing. Understanding how vitality capacityterm·dom affects longitudinal changes in health trajectories is beneficial because it can identify people at risk of developing frailtyterm·dom. Measuring vitality capacityterm·dom over time can give an indication of the level of a person's reserve capacity; this method is dynamic and it can identify changes in capacity over time. Whereas frailtyterm·dom is a rather static approach of evaluating reserve capacity, vitality capacityterm·dom can be conceptualised as a continuum measure across the lifespan of older adults. Because vitality capacityterm·dom can give an overview of the changes in reserve capacity, it is a highly important concept in the context of healthy ageingterm·dom. Therefore, we assume that these two concepts are complementary; a reduction in vitality can lead to a state of susceptibility to stressors, leading to frailtyterm·dom. Measuring vitality capacityterm·dom in the context of frailtyterm·dom can benefit health-care professionals by providing them with information on when to take action to reverse the trend towards frailtyterm·dom. Furthermore, measuring vitality at the population level can incentivise clinicians and policy makers to encourage people to remain healthy in old age, by developing policies to promote healthy ageingterm·dom.
Research has shown that the risks of COVID-19 increases with age. 47 The COVID-19 pandemic and its associated lockdowns and restrictions might conceivably have accelerated the ageing process substantially, 28 by contributing to a decline in the vitality capacityterm·dom of older people, possibly due to a decrease in physical activity during the pandemic. 48 COVID-19 has therefore highlighted the susceptibility of ageing populations to emerging diseases. SARS-CoV-2 infection is characterised by inflammation, muscle weakness, 49 , 50 fatigueterm·key, reduced energy levels, 50 , 51 and reduced pulmonary diffusion capacity; 50 all of which are identified as attributes of vitality capacityterm·dom ( panel 3 ). Therefore, it can be assumed that older adults with reduced vitality are at higher risk of developing COVID-19 than are older adults with higher vitality. This assumption reinforces the importance of monitoring vitality at a population level, allowing appropriate policy decisions to be made during such disease outbreaks and anticipating the effect of associated restrictions on the health of older people.
Inflammageingterm·dom and immunosenescence increase the susceptibility of older people to, and delay recovery from, COVID-19. 52 , 53 Fatigueterm·key is one of the main symptoms of COVID-19. 51 However, lockdown restrictions and the lack of physical activity could have also enhanced feelings of fatigueterm·key in older individuals. Fatigueterm·key is often seen as a marker of age-related accumulation of deficits, representing the underlying vulnerability of an individual's homoeostatic reserves; a sign of biological ageingterm·key. 54 According to Van Kan and colleagues, 55 when the pandemic is over, many people will show accelerated signs of ageing caused by decline in immune function.
The monitoring of vitality should be implemented at different levels, including by older people themselves (via self-testing or via a proxy of vitality levels), by professional health-care providers in their clinical practice, in scientific research, and by creating anonymised dashboards of vitality levels to support real-time vitality monitoring and policy making. The currently available technology already allows for the detection of clinical signs of frailtyterm·dom and dependency. The aim of measuring and monitoring vitality capacityterm·dom is to avoid the occurrence and deterioration of symptoms by providing early warning of declining resistance to health stressors. If self-assessment tools (combined with objective tools) become available to measure vitality, older people will be empowered to manage their lifestyle and behaviour and can achieve further agency over their own ageing trajectory. Therefore, simple, non-invasive, and relatively cheap tools that can give a good overview of an individual's vitality capacityterm·dom should be developed. Health-care professionals need comprehensive longitudinal monitoring of healthy ageingterm·dom trajectories to estimate risks of adverse health outcomes and to deliver personalised care for older people. Monitoring vitality capacityterm·dom can shift the curative view on health care towards a more preventive approach, because information regarding vitality capacityterm·dom is likely to support more tailored interventions and enrich clinical evaluation. Timely identification of older people at risk for declined vitality capacityterm·dom is essential to provide targeted preventive and health-promoting support to optimise healthy ageingterm·dom and wellbeing in older people. Measuring vitality at the population level can provide policy makers with information regarding the vitality level and its trajectories in their communities, to investigate which facilities are necessary to enhance healthy ageingterm·dom. Future research should focus on the optimisation of biomarkersterm·key of vitality capacityterm·dom that can be used in clinical and policy making contexts.
WHO has identified several challenges that must be addressed before vitality capacityterm·dom can be an integral part of health-care systems designed to promote healthy ageingterm·dom. These challenges include developing standardised, valid, and objective tools to assess vitality capacityterm·dom and determining how to monitor this capacity in populations. The current work in vitality capacityterm·dom can be used as a start; however, more research should be done to identify the measurement tools for evaluating vitality capacityterm·dom. That should be the focus for the coming years. First, more research should be done to identify the role of vitality capacityterm·dom across the health span and explore how changes in vitality capacityterm·dom could improve the functional health span. Second, suitable measures for vitality capacityterm·dom that are sensitive to responsiveness and applicable at the population level must be identified. Lastly, because vitality can help to target age-related diseases, understanding how vitality can be improved and which long-term interventions can boost vitality capacityterm·dom to prevent age-related diseases is necessary.
In conclusion, the working group proposed a conceptual working definition that defines vitality capacityterm·dom as a physiological state (due to normal or accelerated biological ageingterm·key processes) resulting from the interaction between multiple physiological systems, reflected in (the level of) energy and metabolism, neuromuscular function, and immune and stress response functions of the body. Defining a conceptual working definition and identifying potential biomarkersterm·key for vitality capacityterm·dom by the experts was the first step. The next step is to perform a systematic review of the potential biomarkersterm·key (blood-based, physical, and self-reported biomarkersterm·key) of vitality capacityterm·dom to develop an operational definition of vitality capacityterm·dom that allows its systematic measurement and monitoring. Further meetings with the working group and projects are planned to expand the operational definition of vitality capacityterm·dom.
Declaration of interests DB reports grants or contracts from the US National Institutes of Health's National Institute on Aging (R21AG054846, R01AG066887, R01AG061378, U01CA164920, R01AG058683, R01AG032282, R01AG057800), the Russel Sage Foundation (BioSS Grant 1810-08987), the Canadian Institute for Advanced Research (CF-0249–CP22-034), Columbia University (Calderone Health Equity Award, Pilot Grant), and Herbert Irving Comprehensive Cancer Center (Pilot Grant); licences from DunedinPACE–TruDiagnostic (no royalties have been received); consulting fees from University of Oslo PROMENTA Center (centre faculty); support for attending meetings or travel from the US National Institutes of Health's National Institute on Aging, Telomere Research Network, Canadian Institute for Advanced Research, University of Oslo PROMENTA Center, and CALERIE Biorepository; participation on a data safety monitoring board or advisory board for Broad River Asset Management; and is a Scientific Advisory Board member at Broad River Asset Management. All other authors declare no competing interests. The authors alone are responsible for the views expressed in this Personal View and does not necessarily represent the views, decisions, or policies of the institutions with which they are affiliated.
Acknowledgments Acknowledgments This Personal View was written in close collaboration with the Ageing and Health unit of WHO (Geneva, Switzerland) and the Frailtyterm·dom in Ageing research department of the Vrije Universiteit Brussel (Brussels, Belgium).
Contributors IB and JAT conceptualised this Personal View and supervised the process of the expert meetings. IB and VK wrote the original draft. IB, VK, and JAT did the data curation, formal analysis, investigation, and methodology of data collection and post-processing, and reviewed and edited the final draft. ABM, JRB, EF, DB, MA-L, CM, MC, YS, TD, and AB revised the manuscript. IB accessed and verified the data.
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