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

PURPOSE: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.