Chronic low water intake is associated with altered exercise-induced oxidative stress and immune cell responses: a cross-sectional study.

Background: Hydration status plays a critical role in modulating oxidative stress during exercise, which can influence physical performance and recovery. While the acute effects of hydration on exercise-induced oxidative stress are well-documented, the long-term impact of chronic water intake remains poorly understood. Therefore, this study aimed to investigate the relationship between chronic low water intake and exercise-induced oxidative stress, as well as changes in the phenotypic composition of peripheral immune cells.

Methods: We assessed the usual plain water intake of the participants (n = 26; 19-29 years) using a questionnaire and classified them as habitually high-water drinkers (HIGH; n = 16; mean plain water intake = 1.22 ± 0.19 L/d) or low-water drinkers (LOW; n = 10; 0.41 ± 0.10 L/d). We conducted a maximal graded exercise test and investigated whether the extent of exercise-induced oxidative stress and immunological changes differed depending on the habitual water intake. Free radical production before and after the exercise test was assessed using serum concentrations of reactive oxygen metabolites (ROMs). The antioxidant capacity to eliminate free radicals was assessed using the serum biological antioxidant potential (BAP). We profiled peripheral blood mononuclear cells (PBMCs; CD4⁺, CD8⁺, CD20⁺, CD14⁺, CD11b⁺, and Annexin V⁺) using fluorescence-activated cell sorting.

Results: At baseline, the LOW group showed higher concentrations of serum ROMs than the HIGH group (p = 0.033). In a maximal graded exercise test, both groups showed comparable performance parameters including peak heart rate, VO₂max, and exercise duration. However, the biochemical responses differed markedly: serum BAP significantly increased in the HIGH group but remained unchanged in the LOW group (p = 0.030). Furthermore, the LOW group showed a larger increase in PBMC apoptosis than the HIGH group, both in absolute cell number and percentage (p = 0.031 and p = 0.034, respectively). The LOW group also showed differential PBMC subset frequencies, with greater CD11b⁺ cell recruitment (p = 0.015) and less pronounced CD14⁺ cell reduction compared to the HIGH group (p = 0.050).

Conclusion: Habitual low water intake was associated with elevated concentrations of free radical by-products in the resting state and impaired antioxidant capacity during acute exercise stress. In response to exercise stress, impaired redox balance in low-water drinkers resulted in accelerated cellular damage and increased myeloid cell recruitment. These findings highlight the importance of maintaining adequate habitual water intake to cope with exercise-induced oxidative stress and prevent excessive cellular stress responses.

Clinical trial registration: Registered at the Clinical Research Information Service (CRIS) on 12 April 2019 (Registry No. KCT0003763).