Functional health index of intrinsic capacity: multi-domain operationalisation and validation in the Singapore Longitudinal Ageing Study (SLAS2)

Declined intrinsic capacity predicts long-term mortality in Chinese older adults: Beijing Longitudinal Study of Aging

BACKGROUND

Intrinsic capacity reflects an individual's functions and capacities across their lifetime. There are few studies on whether the level of intrinsic capacity can predict long-term mortality in Chinese populations.

OBJECTIVE

To explore the effects of intrinsic capacity on long-term outcomes in older Chinese adults.

METHODS

Data were obtained from the Beijing Longitudinal Study of Aging. Overall, 1699 community-dwelling adults aged ≥60 years were included and followed up for 8 years. Intrinsic capacity was determined according to the World Health Organization definition. The predictive ability for adverse outcomes was assessed using the age- and sex-adjusted Cox proportional hazards model.

RESULTS

A decline in intrinsic capacity domains was observed in 729 (42.9 %) participants. Declines in the mobility, cognition, vitality, sensory and psychology domains were observed in 21.8 %, 15.1 %, 11.4 %, 9.10 %, and 14.2 % of the participants, respectively. Low intrinsic capacity was associated with worse physical performance, frailty, social frailty, chronic diseases, fracture, and falls. A greater decline in intrinsic capacity predicted an elevated 8-year mortality rate (decline in overall intrinsic capacity hazard ratio 2.91, 95 % confidence interval 2.44-3.47, P < 0.001; decline in one domain hazard ratio 2.11, 95 % confidence interval 1.71-2.61, P < 0.001; decline in two domains hazard ratio 3.54, 95 % confidence interval 2.81-4.45, P < 0.001; decline in three or more domains hazard ratio 5.30, 95 % confidence interval 4.09-6.87, P < 0.001); adjusted models did not affect prediction performance. Among the five domains of intrinsic capacity, cognition was the strongest predictor of mortality (hazard ratio 3.17, 95 % confidence interval 2.63-3.81, P < 0.001).

CONCLUSIONS

Intrinsic capacity is useful in identifying older adults at higher risk of adverse outcomes, presenting significant implications for healthcare policies in China.

Association of intrinsic capacity with functional decline and mortality in older adults: a systematic review and meta-analysis of longitudinal studies

BACKGROUND

Together with environmental factors, intrinsic capacity (the composite of all the physical and mental capacities of an individual) has been proposed as a marker of healthy ageing. However, whether intrinsic capacity predicts major clinical outcomes is unclear. We aimed to explore the association of intrinsic capacity with functional decline and mortality in older adults.

METHODS

In this systematic review and meta-analysis, we conducted a systematic search in MEDLINE (via PubMed), Scopus, and Web of Science from database inception to Feb 14, 2024, of observational longitudinal studies conducted in older adults (age ≥60 years) assessing the association of intrinsic capacity with impairment in basic activities of daily living (BADL) or instrumental activities of daily living (IADL) or risk of mortality. Estimates were extracted by two reviewers (JLS-S and W-HL) and were pooled using three-level meta-analytic models. The quality of each study was independently assessed by two authors (JLS-S and PLV) using the Newcastle-Ottawa Scale for longitudinal studies. Heterogeneity was evaluated using the I2 indicator at two levels: within-study (level 2) and between-study (level 3) variation. For associations between intrinsic capacity and IADL and BADL, we transformed data (standardised β coefficients and odds ratios [ORs]) into Pearson product moment correlation coefficients (r) using Pearson and Digby formulas to allow comparability across studies. For associations between intrinsic capacity and risk of mortality, hazard ratios (HRs) with 95% CIs were extracted from survival analyses. This study is registered with PROSPERO, CRD42023460482.

FINDINGS

We included 37 studies (206 693 participants; average age range 65·3-85·9 years) in the systematic review, of which 31 were included in the meta-analysis on the association between intrinsic capacity and outcomes; three studies (2935 participants) were included in the meta-analysis on the association between intrinsic capacity trajectories and longitudinal changes in BADL or IADL. Intrinsic capacity was inversely associated with longitudinal impairments in BADL (Pearson's r -0·12 [95% CI -0·19 to -0·04]) and IADL (-0·24 [-0·35 to -0·13]), as well as with mortality risk (hazard ratio 0·57 [95% CI 0·51 to 0·63]). An association was also found between intrinsic capacity trajectories and impairment in IADL (but not in BADL), with maintained or improved intrinsic capacity over time associated with a lower impairment in IADL (odds ratio 0·37 [95% CI 0·19 to 0·71]). There was no evidence of publication bias (Egger's test p>0·05) and there was low between-study heterogeneity (I2=18·4%), though within-study (I2=63·2%) heterogeneity was substantial.

INTERPRETATION

Intrinsic capacity is inversely associated with functional decline and mortality risk in older adults. These findings could support the use of intrinsic capacity as a marker of healthy ageing, although further research is needed to refine the structure and operationalisation of this construct across settings and populations.

FUNDING

None.

TRANSLATIONS

For the Spanish and French translations of the abstract see Supplementary Materials section.

Development and validation of an intrinsic capacity score in the UK Biobank study

BACKGROUND

In 2015, the World Health Organization introduced the concept of intrinsic capacity (IC) to define the individual-level characteristics that enable an older person to be and do the things they value. This study developed an intrinsic capacity score for UK Biobank study participants and validated its use as a tool for health outcome prediction, understanding healthy aging trajectories, and genetic research.

METHODS

Our analysis included data from 45,208 UK biobank participants who had a complete record of the ten variables included in the analysis. Factor adequacy was tested using Kaiser-Meyer-Olkin, Barthelt's, and the determinant of matrix tests, and the number of factors was determined by the parallel analysis method. Exploratory and confirmatory factor analyses were employed to determine the structure and dimensionality of indicators. Finally, the intrinsic capacity score was generated, and its construct and predictive validities as well as reliability were assessed.

RESULTS

The factor analysis identified a multidimensional construct comprising one general factor (intrinsic capacity) and five specific factors (locomotor, vitality, cognitive, psychological, and sensory). The bifactor structure showed a better fit (comparative fit index = 0.995, Tucker Lewis index = 0.976, root mean square error of approximation = 0.025, root mean square residual = 0.009) than the conventional five-factor structure. The intrinsic capacity score generated using the bifactor confirmatory factor analysis has good construct validity, as demonstrated by an inverse association with age (lower intrinsic capacity in older age; (β) =-0.035 (95%CI: -0.036, -0.034)), frailty (lower intrinsic capacity score in prefrail participants, β = -0.104 (95%CI: (-0.114, -0.094)) and frail participants, β = -0.227 (95%CI: -0.267, -0.186) than robust participants), and comorbidity (a lower intrinsic capacity score associated with increased Charlson's comorbidity index, β =-0.019 (95%CI: -0.022, -0.015)). The intrinsic capacity score also predicted comorbidity (a one-unit increase in baseline intrinsic capacity score led to a lower Charlson's comorbidity index, β = 0.147 (95%CI: -0.173, -0.121)) and mortality (a one-unit increase in baseline intrinsic capacity score led to 25 % lower risk of death, odds ratio = 0.75(95%CI: 0.663, 0.848)).

CONCLUSION

The bifactor structure showed a better fit in all goodness of fit tests. The intrinsic capacity construct has strong structural, construct, and predictive validities and is a promising tool for monitoring aging trajectories.

Social determinants of intrinsic capacity: A systematic review of observational studies

BACKGROUND

The World Health Organization defined healthy ageing as the maintenance of functional ability with ageing. Intrinsic capacity is a measurement of healthy ageing, and can be shaped by social determinants. However, an overall understanding of how multiple social determinants contribute to intrinsic capacity remains unclear. We aim to summarize observational studies investigating the relationships between social determinants and intrinsic capacity among community-dwelling adults.

METHODS

A systematic search was conducted through Medline, Embase, PsycInfo, Web of Science, and CINAHL until August 14, 2023.

RESULTS

After reviewing 813 articles, we included 21 studies from nine countries in Asia, Europe, and America. Seventeen studies used a cross-sectional design and the others were longitudinal studies. Social determinants related to intrinsic capacity can be classified into five domains, containing socioeconomic status (16, 76.2% of studies), lifestyles (14, 66.7%), psychosocial factors (9, 42.9%), material circumstances (4, 19.0%), and healthcare systems (1, 4.8%). Strong evidence supported that better intrinsic capacity was associated with higher education, higher wealth, more physical activities, no smoking, more social engagement, and being married or partnered. The relationships of intrinsic capacity with dietary patterns and alcohol drinking were contradictory across studies. Research on the associations of working status, housing environments, and healthcare accessibility with intrinsic capacity was insufficient to draw conclusions.

CONCLUSION

These findings highlight roles of socioeconomic status, lifestyles, and psychosocial factors in improving intrinsic capacity thus promoting healthy ageing. Future research is needed to investigate causal relationships between social determinants and intrinsic capacity, especially material circumstances and healthcare systems.

Measuring healthy ageing: current and future tools

Human ageing is a complex, multifactorial process characterised by physiological damage, increased risk of age-related diseases and inevitable functional deterioration. As the population of the world grows older, placing significant strain on social and healthcare resources, there is a growing need to identify reliable and easy-to-employ markers of healthy ageing for early detection of ageing trajectories and disease risk. Such markers would allow for the targeted implementation of strategies or treatments that can lessen suffering, disability, and dependence in old age. In this review, we summarise the healthy ageing scores reported in the literature, with a focus on the past 5 years, and compare and contrast the variables employed. The use of approaches to determine biological age, molecular biomarkers, ageing trajectories, and multi-omics ageing scores are reviewed. We conclude that the ideal healthy ageing score is multisystemic and able to encompass all of the potential alterations associated with ageing. It should also be longitudinal and able to accurately predict ageing complications at an early stage in order to maximize the chances of successful early intervention.

Association of intrinsic capacity with incidence and mortality of cardiovascular disease: Prospective study in UK Biobank

BACKGROUND

The World Health Organization proposed the concept of intrinsic capacity (IC; the composite of all the physical and mental capacities of the individual) as central for healthy ageing. However, little research has investigated the interaction and joint associations of IC with cardiovascular disease (CVD) incidence and CVD mortality in middle- and older-aged adults.

METHODS

Using data from 443 130 UK Biobank participants, we analysed seven biomarkers capturing the level of functioning of five domains of IC to calculate a total IC score (ranging from 0 [better IC] to +4 points [poor IC]). Associations between IC score and incidence of six long-term CVD conditions (hypertension, stroke/transient ischaemic attack stroke, peripheral vascular disease, atrial fibrillation/flutter, coronary artery disease and heart failure), and grouped mortality from these conditions were estimated using Cox proportional models, with a 1-year landmark analysis to triangulate the findings.

RESULTS

Over 10.6 years of follow-up, CVD morbidity grouped (n = 384 380 participants for the final analytic sample) was associated with IC scores (0 to +4): mean hazard ratio (HR) [95% confidence interval, CI] 1.11 [1.08-1.14], 1.20 [1.16-1.24], 1.29 [1.23-1.36] and 1.56 [1.45-1.59] in men (C-index = 0.68), and 1.17 [1.13-1.20], 1.30 [1.26-1.36], 1.52 [1.45-1.59] and 1.78 [1.67-1.89] in women (C-index = 0.70). In regard to mortality, our results indicated that the higher IC score (+4 points) was associated with a significant increase in subsequent CVD mortality (mean HR [95% CI]: 2.10 [1.81-2.43] in men [C-index = 0.75] and 2.29 [1.85-2.84] in women [C-index = 0.78]). Results of all sensitivity analyses by full sample, sex and age categories were largely consistent independent of major confounding factors (P < 0.001).

CONCLUSIONS

IC deficit score is a powerful predictor of functional trajectories and vulnerabilities of the individual in relation to CVD incidence and premature death. Monitoring an individual's IC score may provide an early-warning system to initiate preventive efforts.

Intrinsic capacity and risk of death: Focus on the impact of using different diagnostic criteria for the nutritional domain

OBJECTIVE

We aimed to estimate the ability of intrinsic capacity (IC) to predict death in community-dwelling older people using different diagnostic criteria to define the nutritional domain.

METHODS

Participants from the Belgian SarcoPhAge cohort were followed from 2013 to the present. Four IC domains were assessed at baseline (data on the sensorial domain were not collected), and considered unsatisfactory below some specific thresholds. The nutritional domain was considered unsatisfactory if baseline malnutrition was present, defined by: 1) MNA-SF ≤11 points; 2) seven versions of the GLIM criteria, varying by the technique used to identify a reduced muscle mass; or 3) the combination of MNA-SF ≤11 points + GLIM criteria. The association between baseline unsatisfactory IC and 9-year mortality was calculated using the odds ratio (OR) adjusted for cofounders.

RESULTS

Among the 534 participants (73.5 ± 6.2 years old; 60.3 % women at baseline), 157 (29.4 %) were dead after 9.3 ± 0.3 years of follow-up. Patients with baseline unsatisfactory IC in the locomotor domain (adjusted OR = 2.31 [95%CI 1.38-3.86]) or psychological domain (adjusted OR = 1.78 [1.12-2.83]) were at higher mortality risk. Regarding malnutrition, unsatisfactory IC in the nutrition domain was strongly associated with a higher mortality risk, whatever the criteria used to identify a reduced muscle mass. The highest association with mortality was found in participants with a baseline unsatisfactory nutritional domain defined by the combination of MNA-SF + GLIM criteria (adjusted OR = 3.27 [95%CI 1.72-6.23]).

CONCLUSIONS

Presenting any unsatisfactory IC at baseline was associated with a higher 9-year mortality risk in community-dwelling older people. The sequential incorporation of MNA-SF and GLIM criteria as the IC nutritional domain would be helpful to guide public health actions towards healthy ageing.

Measuring healthy ageing: current and future tools

Human ageing is a complex, multifactorial process characterised by physiological damage, increased risk of age-related diseases and inevitable functional deterioration. As the population of the world grows older, placing significant strain on social and healthcare resources, there is a growing need to identify reliable and easy-to-employ markers of healthy ageing for early detection of ageing trajectories and disease risk. Such markers would allow for the targeted implementation of strategies or treatments that can lessen suffering, disability, and dependence in old age. In this review, we summarise the healthy ageing scores reported in the literature, with a focus on the past 5 years, and compare and contrast the variables employed. The use of approaches to determine biological age, molecular biomarkers, ageing trajectories, and multi-omics ageing scores are reviewed. We conclude that the ideal healthy ageing score is multisystemic and able to encompass all of the potential alterations associated with ageing. It should also be longitudinal and able to accurately predict ageing complications at an early stage in order to maximize the chances of successful early intervention.

Measurements of Intrinsic Capacity in Older Adults: A Scoping Review and Quality Assessment

OBJECTIVES

This review summarizes the measurements of intrinsic capacity in 5 domains across different studies and evaluates the quality of research papers.

DESIGN

Scoping review of papers written in English and Chinese published in peer-reviewed journals.

SETTING AND PARTICIPANTS

The intrinsic capacity of older adults was assessed using the multidomain structure (Cognition, Locomotion, Psychological, Sensory and Vitality) proposed by the World Health Organization.

METHODS

We searched PubMed, MEDLINE, and Web of Science for papers in English, and CNKI, CBM for papers written in Chinese published until September 13, 2022. Both cross-sectional and cohort studies of multidomain measurements of intrinsic capacity were included. Three independent reviewers appraised the quality of studies, and Cohen's kappa was calculated to determine interrater reliability. Data were listed by author, year, setting, country, age range and number of participants, measurement and calculation of intrinsic capacity, and data acquisition method.

RESULTS

We included 53 studies. Twenty-one studies were of high quality, 31 studies were of moderate quality, and 1 study was of low quality. Measurements of intrinsic capacity and derivation of the summative index score were heterogeneous. Intrinsic capacity was usually assessed in 4 or 5 domains. Sensory was the most frequently overlooked domain or subdivided into vision and hearing in some studies. Indicators of vitality were the most heterogeneous. We also found consistency in heterogeneous measurements. The most common measurements of cognition, locomotion, and psychological capacity were the Mini-Mental State Examination, Short Physical Performance Battery, and Geriatric Depression Scale respectively. Self-reported questionnaires were commonly adopted in sensory domain. The Mini-Nutritional Assessment and grip strength were the most measured indicators of vitality.

CONCLUSIONS AND IMPLICATIONS

The focus on capacity and disease should be balanced to better promote healthy aging in older adults. Heterogeneity of intrinsic capacity measurements underscores the need for consensus about standardized measurements and calculation procedures.