Letter to “Cross‐Sectional Associations of Integrated Lifestyle‐Related Factors With Intrinsic Capacity in Community‐Dwelling Older Adults: The Kashiwa Cohort Study”

1.

We read with great interest the article by Lyu et al. [1], which examined cross‐sectional associations between integrated lifestyle related factors and intrinsic capacity (IC) among older adults living in the community. The authors should be congratulated for addressing an important topic within the World Health Organization's Integrated care for Older People (ICOPE) framework and for highlighting the contribution of multidimensional lifestyle factors to healthy aging, as maintaining IC has become a major focus of geriatric medicine. Nevertheless, we would like to highlight several methodological considerations that may influence the interpretation of the reported findings.

First, an important concern is the conceptual overlap between exposure variables and outcome measures. The authors well evaluated the physical lifestyle using variables like walking duration and regular exercise, while locomotion constituted one of the five domains of composite IC score. Similarly, nutrition related factors included dietary diversity and oral function; the vital domain of IC was assessed using the Mini Nutritional Assessment which also reflects nutritional status. Because closely related constructs contributed to both the independent variables and dependent outcomes, the observed results may have been partially driven by shared measurements rather than representing independent relationships. Future investigations could minimize this concern by using the exposure variables that are distinct from the domains included in IC outcomes. As discussed by de Vet et al. [2], construct validity requires that predictor and outcome measures represent distinct constructs. The overlap between the physical and nutritional lifestyle domains and components of IC has contributed to overestimation of reported associations.

Second, the exclusion of the participants with Mini‐Mental State Examination (MMSE) scores of < 18 may have introduced selection bias. Although this decision was made to improve the reliability of assessments, individuals with severe cognitive impairment are most likely to exhibit poor IC, reduced physical activity, and nutritional deficiency. So excluding these participants may have produced a healthier study population and applicability of findings to older adults with greater functional capability. Excluding participants with severe cognitive impairment may have introduced selection bias, potentially affecting the accuracy of findings as outlined in standard epidemiological methodology by Hernan and Robins [3].

Third, the construction of composite IC score deserves further consideration. The authors acknowledged that no universally accepted approach currently exists for generating a composite IC score and therefore developed a confirmatory factor analysis (CFA)‐weighted index. While this represents a statistically meticulous approach, the resulting score is sample specific and depends on the factors derived and type of methodology used. Consequently, comparisons with previous studies that have used alternate scoring methods may be challenging. Broader standardization of IC measurement can facilitate comparisons across different populations and healthcare settings. As noted by Beard et al. [4], there is currently no universally accepted approach for constructing a composite IC score. Consequently, use of sample specific CFA weighted score may reduce comparability across different populations.

Finally, although the authors adjusted their analysis for several potential confounding factors, the inclusion of appendicular skeletal muscle mass index (ASMI) deserves further clarification. Muscle mass depends on regular physical activity and may lie on the pathway through which physical activity improves IC. Therefore, adjusting for muscle ASMI may have reduced the observed effect of physical activity on IC, leading to underestimation of its true association. Explaining the reason for including ASMI in fully adjusted model would help the readers better interpret the findings. As discussed by Lederer et al., adjustment for mediators rather than true confounders may attenuate the observed association [5].

Despite these considerations, this study provides valuable evidence supporting the association between multidimesional lifestyle‐related factors and IC in older adults. Future prospective studies employing standardized IC assessment methods, minimizing conceptual overlap between exposures and outcomes, including participents across broader spectrum and eliminating selection bias will be essential in determining whether the associations are casual and to guide effective interventions required for preserving IC during aging.

We congratulate the authors for their important contribution and hope these comments stimulate further discussion and future research in this evolving field.

Funding

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Ethics Statement

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Conflicts of Interest

The author declares no conflicts of interest.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.