Association of physical activity and hydration markers with cellular health in older adults: A doubly labeled water study

This study aimed to determine the associations between the phase angle (PhA), extracellular water-to-intracellular water ratio (ECW/ICW), physical activity levels (PALs) measured using the doubly labeled water (DLW) method, and the time spent engaging in physical activities of varying intensities in older adults living in Japan. This study was part of the Kyoto-Kameoka prospective cohort study of older adults. The PhA and ECW/ICW ratio were measured using a multi-frequency bioelectrical impedance analysis device. PAL, percentage body fat, and fat-free mass index were calculated using the DLW method, while the average daily moderate-to-vigorous physical activity (MVPA), high-intensity light physical activity (HLPA), low-intensity light physical activity, and sedentary behavior durations were quantified using a triaxial accelerometer. Adjusted partial order correlation analysis showed significant positive correlations between the PhA and PAL (p = 0.001), as well as between the PhA and the MVPA (p = 0.027) and HLPA (p = 0.023) durations. The PAL was also significantly negatively correlated with the ECW/ICW ratio (p = 0.008). Adjusted multiple regression analysis confirmed that PAL (p = 0.004) and HLPA (p = 0.025) were significantly positively associated with PhA and negatively associated with ECW/ICW ratio (p = 0.004 and p = 0.036, respectively). PAL, measured using the precise DLW method, is an explanatory factor for PhA and ECW/ICW ratio. HLPA below the MVPA threshold was linked to more favorable hydration markers of cellular health in older adults. As this was a cross-sectional study, causality cannot be inferred.