Abstract
Aging is characterized by gradual shifts in cellular and physiological processes, even in individuals who remain apparently clinically healthy. These changes reflect a coordinated decline in metabolic efficiency, immune regulation, organ function, psychological resilience, and sleep integrity, domains increasingly recognized as interconnected determinants of apparently healthy aging. This study explored age- and sex-associated patterns in multidimensional physiological domains and gut microbiota features among 45 apparently healthy middle-aged and elderly participants across four age–sex groups (middle-aged males, n = 13; middle-aged females, n = 11; elderly males, n = 13; elderly females, n = 8). Comprehensive clinical, metabolic, inflammatory, hepato-renal, psychological, and sleep parameters were standardized into domain-specific Z-scores, which were integrated into a composite multidimensional physiological health index (MPHI), a systems-level physiological index developed as a proxy for physiological processes associated with mitochondrial function and apparently healthy aging rather than a direct measure of mitochondrial biology. Whole-metagenome sequencing and MetaPhlAn-based taxonomic profiling were used to characterize gut microbiota composition and diversity. Despite no statistically significant overall differences among the four age–sex groups in multivariate analysis (MANOVA, p = 0.103) and gut microbial community structure (PERMANOVA, p = 0.651), descriptive variation was observed across several physiological domains, while microbiota–host associations remained exploratory and nominal after FDR correction. Middle-aged males showed comparatively less favorable metabolic and inflammatory profiles, while selected psychosocial and sleep-related measures showed variation across the age–sex groups, particularly among elderly females. Principal component analysis (PCA) of domain scores indicated multidimensional physiological variation influenced by inflammatory, metabolic, and hepato-renal indices, although substantial overlap was observed among the age–sex groups. The MPHI showed descriptive variation across the groups, with elderly males showing the highest composite scores and middle-aged females the lowest. Overall, the apparently healthy cohort showed subtle variation across interconnected physiological domains in the absence of overt differences in gut microbial community structure. These findings support the potential utility of composite physiological indices for exploratory characterization of multidimensional physiological variation during aging, while highlighting the need for validation in larger independent cohorts and against direct mitochondrial biomarkers.