A shift in perspective: from disease to capacity

Intrinsic Capacity is a concept introduced by the WHO to describe healthy ageing through a focus on the capacities individuals retain, rather than the diseases they may develop⁽¹⁾. It refers to the composite of all physical and mental capacities that a person can draw upon throughout life and is considered essential for maintaining functional ability, which supports well-being in older age^{(Reference Beard, Officer and de Carvalho2)}. Intrinsic capacity comprises five interconnected domains: vitality, sensory, cognition, psychology, and locomotion^{(Reference Beard, Jotheeswaran and Cesari3,Reference Cesari, Araujo de Carvalho and Amuthavalli4)} . Vitality reflects the body’s physiological reserve, including aspects such as energy balance, nutritional status, and metabolic health^{(Reference Bautmans, Knoop and Amuthavalli Thiyagarajan5)}. The sensory domain encompasses vision and hearing, both of which are critical for communication, environmental interaction, and safety. Cognition includes mental processes such as memory, attention, and executive function, which are important for autonomy and decision-making. The psychology domain captures emotional well-being, mood regulation, and resilience in the face of stress or change. Finally, locomotion represents the ability to move independently and maintain physical mobility, which is closely linked to daily functioning and independence. Together, these domains provide a holistic view of an individual’s intrinsic capacity⁽⁶⁾. In the context of ageing, intrinsic capacity offers a shift away from disease-cantered models toward a more functional and person-oriented perspective. This shift highlights the importance of continuous assessment and early intervention, making intrinsic capacity a valuable framework for monitoring older adults’ health and the prevention of functional decline. Building on this foundation, this review explores the specific challenges and opportunities in positioning nutritional status as a core component of the vitality domain.

Monitoring intrinsic capacity offers a comprehensive and proactive approach to understanding health trajectories in older adults. Moreover, by monitoring IC over time, it becomes possible to identify early signs of decline and tailor interventions that help maintain quality of life and independence in older adults. For instance, studies show that lower intrinsic capacity is associated with increased risks of adverse health outcomes, such as disability in activities of daily living, nursing home admissions, and mortality^{(Reference Yang, Ma and Wei7–Reference Li, Zhang and Li10)}. Practical implementations of intrinsic capacity monitoring are already emerging. One practical application is the Integrated Care for Older People (ICOPE) screening tool, which was designed to detect impairments in IC domains among older adults⁽¹¹⁾. Additionally, platforms such as CAREUP^{(Reference Kolakowski, Lupica and Ben Bader12)} were designed to continuously monitor intrinsic capacity through personalised assessments and use machine-learning algorithms to predict future health trajectories. Beyond these early practical tools, researchers have also begun to optimise the operationalisation of intrinsic capacity using existing (cohort) data. These endeavours enable the examination of intrinsic capacity over time and provide insight into its predictive validity in diverse populations. For instance, studies using data from the Survey of Health, Aging, and Retirement in Europe (SHARE) and other longitudinal cohorts have demonstrated strong associations between lower intrinsic capacity scores and greater subsequent declines in activities of daily living^{(Reference Chen, Hanewald and Si13)}.

Nutritional status through the lens of intrinsic capacity

Intrinsic capacity encompasses multiple domains, among which vitality is particularly relevant to nutritional status and overall health^{(Reference Cesari, Sadana and Sumi14)}. The interconnected nature of these domains is visually represented in Figure 1, where the central construct of intrinsic capacity is comprised of the five core domains. By definition, 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^{(Reference Bautmans, Knoop and Amuthavalli Thiyagarajan5)}. Nutrition is a fundamental component of vitality, as adequate nutritional intake supports processes such as energy metabolism, muscle preservation, and immune function. Consequently, sub-optimal dietary intake (i.e. the over- or underconsumption of nutrients through the diet) and poor nutritional status (i.e. undernutrition or obesity) can directly undermine vitality, leading to diminished resilience, increased susceptibility to illness, and accelerated decline in overall capacities. Beard and colleagues further suggested that intrinsic capacity domains are not at parallel levels; instead, vitality might serve as an underlying capacity and influences the manifestations of the other more overtly expressed IC domains^{(Reference Beard, Jotheeswaran and Cesari3,Reference Beard, Si and Liu15)} . Taken together, the integration of nutritional factors within the vitality domain of intrinsic capacity could offer valuable insights, enabling targeted interventions to mitigate functional decline and enhance healthy ageing. The WHO, through its ICOPE guidelines⁽¹¹⁾, recommends assessing vitality by screening through nutritional status^{(Reference Cederholm, Jensen and Correia16,17)} . One study has reported that appetite and unintentional weight loss significantly correlate with impairments in other intrinsic capacity domains, particularly the psychology and locomotion domains^{(Reference Gaussens, González-Bautista and Bonnefoy18)}. In conclusion, monitoring intrinsic capacity would inherently provide valuable insights into nutritional status, particularly through the vitality domain.

Figure 1 The domains of Intrinsic Capacity as defined by the World Health Organization.

Challenges and opportunities in integrating nutritional measures into intrinsic capacity monitoring

The intrinsic capacity framework and the vitality domain provide a valuable lens through which to view and apply traditional nutritional assessments. The very same markers used to assess nutritional status in aging research are also applied in clinical nutrition regardless of age. Rather than replacing these assessments, the intrinsic capacity framework emphasises how they can be leveraged to provide a more holistic understanding of an individual’s physiological reserve. For example, the Global Leadership Initiative on Malnutrition (GLIM) criteria are not age-specific and can be used in aging research, but it remains important to bear in mind that age is included as a risk factor^{(Reference Cederholm, Jensen and Correia16,Reference Norman, Haß and Pirlich19,Reference Jensen, Cederholm and Correia20)} . While handgrip strength is a traditional measure of muscle function, within the context of vitality it can be used as a key indicator of overall physiological reserve^{(Reference Lu, González-Bautista and Guyonnet21,Reference Sayer and Kirkwood22)} . Similarly, anthropometric assessments such as calf circumference provide a crude measure of muscle mass and can serve as a proxy for nutritional status^{(Reference Bonnefoy, Jauffret and Kostka23)}. Dietary assessments and questionnaires, which measure appetite and nutritional intake, offer insights into the foundational support for a person’s energy and metabolism. Finally, biomarkers such as albumin, C-reactive protein, and haemoglobin, which are used to identify inflammation and nutrient deficiencies, can be viewed as markers of the immune and stress response functions of the body, which are core components of vitality^{(Reference Lu, González-Bautista and Guyonnet21,Reference Silva, Martinez and Rolland24)} . By theoretically integrating these indicators, the intrinsic capacity framework provides a comprehensive, multi-faceted view of an individual’s nutritional status as an underlying factor of overall health.

Although the vitality domain holds clear potential for capturing nutrition-related decline within the intrinsic capacity framework, its practical application remains challenging. At present, there is no consensus on how vitality should be operationalised in clinical or research contexts^{(Reference Bautmans, Knoop and Amuthavalli Thiyagarajan5,Reference Gonzalez-Bautista, Andrieu and Gutiérrez-Robledo25)} . For example, the ICOPE handbook refers to ‘malnutrition’ when addressing declines in the vitality domain and suggests four instruments for nutritional screening: the Mini Nutritional Assessment (MNA)^{(Reference Vellas, Guigoz and Garry26)}, the Malnutrition Universal Screening Tool (MUST)^{(Reference Stratton, Hackston and Longmore27)}, the Seniors in the Community Risk Evaluation for Eating and Nutrition questionnaire (SCREEN II)^{(Reference Keller, Goy and Kane28)}, and the Short Nutritional Assessment Questionnaire 65+ (SNAQ65+)^{(Reference Power, Mullally and Gibney29)}. Notably, some of these tools, such as the MNA, SCREEN II, and SNAQ65+, are specifically designed or validated for older adult populations, directly aligning with the age-centric focus of the intrinsic capacity framework. However, it does not provide a unified framework on how these tools should be applied within the context of intrinsic capacity, nor does it specify which indicators should be prioritised. Consequently, due to this lack of standardisation, many operationalisations of the vitality domain do not explicitly include nutritional measures^{(Reference Chen, Kukreti and Yang30–Reference López-Ortiz, Lista and Peñín-Grandes35)}. Stolz et al. ^{(Reference Stolz, Mayerl and Freidl36)} assessed vitality using only handgrip strength and forced expiratory volume. Beard et al. ^{(Reference Beard, Jotheeswaran and Cesari3)} expanded this approach by including biomarkers such as dehydroepiandrosterone and haemoglobin alongside grip strength and forced expiratory volume. Even when nutritional status measure is included, the specific indicators such as appetite, weight change, and nutritional status vary considerably across studies, which limits comparability and consistency. For instance, in Cheong et al. ^{(Reference Cheong, Yap and Nyunt37)}, the vitality domain was operationalised using a combination of forced expiratory volume, the Elderly Nutritional Indicators for Geriatric Malnutrition Assessment, the Nutritional Screening Initiative, and three energy-related items from the SF-12 questionnaire. Huang et al. ^{(Reference Huang, Okada and Matsushita38)} assessed vitality using both the MNA and handgrip strength. In contrast, Liu et al. ^{(Reference Liu, Kang and Liu39)} and Sánchez-Sánchez et al. ^{(Reference Sánchez-Sánchez, Rolland and Cesari40)} relied solely on the short form of the MNA, while Locquet et al. ^{(Reference Locquet, Sanchez-Rodriguez and Bruyère41)} and Zhao et al. ^{(Reference Zhao, Chhetri and Chang42)} used the full MNA. These inconsistencies highlight key challenges in integrating nutritional measures into the vitality domain of intrinsic capacity. We should also acknowledge that the conceptual and operational framework of healthy ageing, including intrinsic capacity, is still evolving. In practice, intrinsic capacity is often measured using variables originally collected for other research or clinical purposes. As a result, data availability frequently constrains researchers’ ability to select consistent and domain-relevant indicators to measure the construct. This contributes to the overall lack of standardisation, which affects the comparability of findings across studies. While this challenge is not unique to the vitality domain, it is particularly pronounced in this area due to the non-specific nature of the term ‘vitality’ and the absence of an established definition. In contrast, domains such as sensory or cognition tend to rely on more established measures. The conceptual vagueness of vitality makes its operationalisation especially difficult, suggesting the need for clearer definitions and agreed-upon indicators in future work.

These conceptual and practical challenges have also influenced our own efforts to operationalise vitality. We used data from the Longitudinal Aging Study Amsterdam (LASA), a nationally representative cohort of older adults in the Netherlands, to develop standardised, longitudinal measures of intrinsic capacity^{(Reference Hoogendijk, van Schoor and Qi43,Reference Qi, Schaap and Schalet44)} . Following a stepwise approach, we identified 22 candidate indicators across the five domains based on literature and expert consultation. We then applied unidimensional factor analysis within each domain to test whether the indicators captured a coherent construct, followed by a partial least squares structural equation model to examine the structure of intrinsic capacity as a whole. This approach allowed us to construct both domain-specific and composite scores. The vitality domain, in particular, posed notable challenges due to the absence of clear operational guidance. While nutritional status is theoretically central to vitality, we found it difficult to capture this construct empirically. We evaluated several physiological indicators, including handgrip strength, peak flow, calf circumference, appetite, sleep quality, BMI and weight change. After thorough analyses, hand grip strength, peak flow, and calf circumference were selected to construct the domain score for vitality. Handgrip strength and peak flow have frequently been used as proxies for physiological reserve^{(Reference Beard, Jotheeswaran and Cesari3,Reference Beard, Si and Liu15,Reference Aliberti, Bertola and Szlejf45)} , while calf circumference is a recognised marker of nutritional status^{(Reference Bonnefoy, Jauffret and Kostka23,Reference Cruz-Jentoft, Bahat and Bauer46)} . Interestingly, indicators such as BMI and weight change, although often used in clinical nutrition assessments, were not selected due to low factor loadings and weak correlations with the vitality construct in our sample. This discrepancy may reflect the temporal dynamics of change, where declines in functional performance, such as grip strength, occur earlier or at the same time as anthropometric changes like weight loss or altered BMI^{(Reference McGrath, Kraemer and Snih47–Reference Jeong, Choi and Kim49)}. Different markers may therefore be relevant at different stages of aging, which aligns with the ICOPE distinction between basic screening and in-depth assessment⁽¹⁷⁾. Further, it is also important to note that measures commonly applied in research are not always suitable for clinical practice, given differences between patients and community-dwelling populations. Moreover, the exclusion of indicators such as BMI and weight change from the vitality domain of our intrinsic capacity measure was determined in a data-driven manner and based solely on LASA data. This highlights the challenge of selecting indicators that not only reflect theoretical definitions but also perform well empirically. Our findings suggest the need for more work to clarify the construct of vitality and improve its operationalisation in both clinical and research settings.

Advancing the use of intrinsic capacity in nutrition research and practice

The potential of intrinsic capacity to support more holistic and proactive approaches in nutritional monitoring remains significant. Yet, as the WHO has acknowledged, several challenges must be addressed before vitality capacity can be fully integrated into health-care systems designed to promote healthy ageing^{(Reference Bautmans, Knoop and Amuthavalli Thiyagarajan5,Reference Cesari, Sadana and Sumi14)} . These include the development of standardised, valid, and objective tools to assess vitality and the establishment of effective approaches to monitor this at the population level.

To move forward, two key areas require focused attention. First, consensus needs to be reached that nutritional status should be considered an essential component of the vitality domain. By definition, nutrition is a fundamental component of vitality, yet it is not consistently incorporated in operationalisations of this domain. When nutrition measures are included, the indicators used vary widely. Building on this, agreement is needed on which nutritional measures should be included when assessing vitality. Achieving consensus on core items will support harmonised operational definitions and improve comparability across studies and settings. The incorporation of the GLIM) consensus of diagnosing malnutrition could be a potential step forward, especially since the GLIM framework has been widely adopted and has showed strong construct and predictive validity^{(Reference Jensen, Cederholm and Correia20)}.

Second, it is important to reach consensus on the scoring system. Empirical analyses are needed to determine the most appropriate method for constructing scores that accurately reflect the underlying capacity⁽⁵⁰⁾. This issue is relevant for intrinsic capacity as a whole and the domains of intrinsic capacity separately. Specifically for vitality, for instance, nutrition measures often differ in format. Some measures, such as the Mini-Nutritional Assessment, yield continuous scores, while others, like unintentional weight loss, are typically recorded as binary responses Achieving consensus on which items to include and how to standardise their scaling will support harmonised operational definitions and improve comparability across studies and settings. This includes testing scoring approaches on pilot datasets to evaluate construct validity, predictive power, sensitivity to change, and practical applicability. Importantly, any method adopted should strike a balance between statistical robustness and feasibility in real-world implementation. Once appropriate and responsive vitality measures are identified, further research will be necessary to understand how vitality evolves during ageing and how its changes relate to broader functional outcomes. A clearer understanding of these relationships could enable targeted interventions aimed at extending functional health, thereby improving quality of life for ageing populations.