Associations Between Physical Activity, 24-hour Urinary Hydration Markers And Timing Of Fluid Intake

Abstract

PURPOSE: Appropriate fluid intake is important to offset water losses induced by physical activity. However, limited research has investigated the relationships between physical activity and fluid intake in free living individuals. To assess the associations between objective and subjective measures of physical activity, reported fluid intake, and urinary hydration biomarkers in free living emerging adults. METHODS: Thirty-four participants (44% female; age, 23 ± 4 years; height, 172.9 ± 10.3 cm; body mass, 77.2 ± 18.1 kg; body fat, 18.4 ± 8.4%) provided a 24 h urine sample across seven consecutive days for measures of urine volume (UVOL), urine osmolality (UOSMO), urine specific gravity (USG) and urine color (UCOL). A validated fluid log was used to record fluid intake each day, where fluid intake was segmented into morning (waking - noon), afternoon (noon - 5 pm) and evening (5 pm - sleep). Physical activity was objectively assessed using wrist-worn actigraphy and analyzed using standard cutoffs. Subjective assessment of physical activity quantified day-level physical activity and was measured by MET-minutes. RESULTS: Over 7 consecutive days, participants participated in 16.97 ± 23.42 minutes of moderate-to-vigorous physical activity (MVPA) and 677.89 ± 702.62 MET-minutes of activity per day. Mean 7-day fluid consumption was 2551 ± 1056 mL and corresponding mean 7-day UVOL, UOSMO, USG, and UCOL was 1699 ± 865 mL, 567 ± 210 mOsm/kg, 1.020 ± 0.010 AU, and 3.9 ± 1.0 AU, respectively. Increased MVPA (adj R2 = 0.114, p = 0.044) and increased total MET-minutes (adj R2 = 0.192, p = 0.005) was associated with decreased 24 h USG. Greater morning and evening fluid consumption was associated with increased 24 h UVOL (adj R2 = 0.589, P = 0.02; P < 0.0001). Greater evening fluid intake was associated with lower 24 h UOSMO (adj R2 = 0.331, P = 0.01). CONCLUSIONS: Increasing day-level physical activity in addition to consuming a greater volume of fluids in the morning and evening improved hydration status as reflected by 24 h urinary hydration variables. Further work is needed to explore the associations between physical activity and timing of the fluids consumed. Grant or Funding Information: This study was funded by a University of North Carolina at Greensboro Office of Research Engagement New Faculty Grant.