Ways of Measuring the Intrinsic Capacity Domain of Vitality

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Abstract and Introduction
Methods
Results
Discussion
Conclusion
References
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Abstract and Introduction

Abstract

Background: Vitality is conceptually considered as the underlying capacity influencing other intrinsic capacity (IC) domains and being related to nutrition, physiological reserve and biological ageing. However, there is no consensus on its operationalisation.

Objective: To investigate the structure and magnitude of the association of vitality with other IC domains and functional difficulties using three operational definitions of vitality.

Methods: We included 1,389 older adults from the Multidomain Alzheimer Preventive Trial with data on Mini Nutritional Assessment (MNA), handgrip strength and plasma biomarkers (comprising inflammatory and mitochondrial markers). Using path analysis, we examined the effects of vitality on difficulties in basic and instrumental activities of daily living (ADL and IADL) exerted directly and indirectly through the mediation of other IC domains: cognition, locomotion, psychological, vision and hearing. We further explored the longitudinal association of vitality with IC domains, ADL and IADL over 4 years using linear mixed-effect regression.

Results: We observed significant indirect effects of vitality on IADL, mainly through cognitive, locomotor and psychological domains, regardless of the vitality measurement. Participants with higher vitality had fewer IADL difficulties at follow-up (MNA score: β [95% CI] = −0.020 [−0.037, −0.003]; handgrip strength: −0.011 [−0.023, 0.000]; plasma biomarker-based index: −0.015 [−0.028, −0.002]). Vitality assessed with the plasma biomarker-based index predicted improved locomotion over time.

Conclusion: Vitality was associated with disability primarily through the mediation of other IC domains. The three indicators examined are acceptable measurements of vitality; biomarkers might be more suitable for the early detection of locomotion decline.

Introduction

According to the World Health Organization (WHO), an individual's functional ability is determined by intrinsic capacity (IC), the environment and the interactions between the two.^[1,2] IC is defined as 'the composite of all physical and mental capacities'^[1] and is often operationalised by five constructs: cognition, locomotion, psychological, sensory (vision and hearing) and vitality.^[2] This IC construct has been validated using population-based data from different countries.^[3–6] Beard and colleagues further suggested that IC domains are not at parallel levels; instead, vitality serves as an underlying capacity and influences the manifestations of the other more overtly expressed IC domains.^[3,4] In other words, how vitality contributes to overall functional capacity is partially by modulating other IC domains.

There is a lack of consensus on measuring the IC domain of vitality in the literature.^[7] The concept of vitality, a capacity to maintain homeostasis to function properly, is derived from the evidence showing that imbalanced energy intake and expenditure (e.g. weight loss, abnormal body mass index) was a strong predictor of disability in older people.^[2] Following this definition, the WHO programme Integrated Care for Older People suggests using nutritional status assessments, such as the Mini Nutritional Assessment (MNA), to evaluate older individuals' vitality.^[8] On the other hand, the concept of vitality is similar to 'physiological reserve' and 'biological age'.^[9] That is, vitality can be understood as the sum of all functions of physiological and biomolecular systems that resist the challenges and determine lifespan and healthspan. In this sense, handgrip strength, a vital sign of physiological reserve^[10] and biological age,^[11] was often used to measure vitality.^[3–6] Biomarkers related to ageing mechanisms at the biomolecular level can be promising indicators of vitality, considering they reflect homeostatic dysregulation since the subclinical stage. To our knowledge, no study has used a combination of plasma biomarkers to operationalise vitality. Furthermore, the most appropriate operational definition of vitality is unknown since no investigation compared the performance of different vitality operationalisations as a structural component of the IC model and an element associated with the evolution of the other IC domains and functional ability over time.

This study aimed to investigate the pathways that connect vitality with functional difficulties (i.e. basic and instrumental activities of daily living—ADL and IADL), directly and indirectly through the overt IC domains (cognition, locomotion, psychological, sensory [vision and hearing]) in older adults. Three vitality measurements reflecting energy balance, physiological reserve and biology of ageing were examined: nutritional status, handgrip strength and a combination of plasma ageing-related biomarkers. Moreover, we evaluated the association of vitality with longitudinal changes in other IC domains, ADL and IADL.

Table 1. Total, direct and indirect standardised effects from vitality to change in ADL and IADL.
	Vitality measurement
	MNA score		Handgrip strength		Plasma biomarkers
	Standardised coefficient (SE)	P	Standardised coefficient (SE)	P	Standardised coefficient (SE)	P
Outcome: ΔADL difficulties
Total effect	−0.152 (0.074)	0.040	−0.042 (0.049)	0.392	−0.058 (0.057)	0.303
Total indirect effect	−0.067 (0.044)	0.133	−0.064 (0.035)	0.069	0.043 (0.041)	0.300
Direct effect	−0.085 (0.074)	0.250	0.021 (0.050)	0.670	−0.101 (0.068)	0.136
Outcome: ΔIADL difficulties
Total effect	−0.004 (0.059)	0.941	−0.014 (0.058)	0.814	−0.032 (0.095)	0.737
Total indirect effect	−0.085 (0.025)	0.001	−0.068 (0.027)	0.011	0.077 (0.033)	0.021
Direct effect	0.081 (0.071)	0.255	0.054 (0.050)	0.278	−0.108 (0.093)	0.242

Table 2. Linear mixed-effect regression examining longitudinal association of vitality with other IC domains, ADL and IADL.
Outcome	Vitality measurement
	MNA score (N = 599)			Handgrip strength (N = 1,283)			Bio-vitality index(N = 874)
	n	β (95% CI)	P	n	β (95% CI)	P	n	β (95% CI)	P
Cognition: MMSE	590	−0.015 (−0.061, 0.032)	0.535	1,258	0.004 (−0.025, 0.033)	0.799	855	−0.023 (−0.058, 0.010)	0.173
Locomotion: SPPB	591	0.037 (−0.013, 0.086)	0.143	1,264	0.018 (−0.013, 0.049)	0.262	855	0.050 (0.010, 0.090)	0.015
Psychological: GDS	590	−0.009 (−0.066, 0.049)	0.771	1,257	0.027 (−0.010, 0.064)	0.154	855	−0.030 (−0.075, 0.015)	0.190
Vision: Monoyer score	584	0.035 (−0.132, 0.202)	0.680	570	−0.091 (−0.266, 0.084)	0.307	381	0.035 (−0.143, 0.214)	0.698
Hearing: HHIE-S	593	−0.100 (−0.544, 0.345)	0.660	579	0.189 (−0.284, 0.663)	0.433	390	0.138 (−0.412, 0.689)	0.622
ADL difficulties	595	−0.017 (−0.026, −0.008)	<0.001	1,267	−0.008 (−0.014, −0.002)	0.009	859	−0.004 (−0.011, 0.003)	0.271
IADL difficulties	595	−0.020 (−0.037, −0.003)	0.018	1,267	−0.011 (−0.023, 0.000)	0.047	859	−0.015 (−0.028, −0.002)	0.027

All models were adjusted for age, sex, education and MAPT group allocation. The coefficient (β) indicates the annual change from 12 months in each outcome (IC domain, ADL or IADL) per SD increment in vitality measurement. Higher MMSE, SPPB and Monoyer values indicate better function, whereas higher GDS, HHIE-S, ADL difficulties and IADL difficulties indicate worse function.

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Investigating Three Ways of Measuring the Intrinsic Capacity Domain of Vitality: Nutritional Status, Handgrip Strength and Ageing Biomarkers

Abstract and Introduction

Abstract

Introduction

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