Fluid replacement following dehydration reduces oxidative stress during recovery

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Abstract

To investigate the effects of hydration status on oxidative DNA damage and exercise performance, 10 subjects ran on a treadmill until exhaustion at 80% VO2max during four different trials [control (C), 3% dehydration (D), 3% dehydration + water (W) or 3% dehydration + sports drink (S)]. Dehydration significantly decreased exercise time to exhaustion (D < C and S). Plasma MDA levels were significantly higher at pre-exercise in D than C. Plasma TAS was significantly lower at pre-exercise in C and S than in D, and was significantly lower in S than D at 60 min of recovery. Dehydration significantly increased oxidative DNA damage during exercise, but fluid replacement with water or sports drink alleviated it equally. These results suggest that (1) dehydration impairs exercise performance and increases DNA damage during exercise to exhaustion; and (2) fluid replacement prolongs exercise endurance and attenuates DNA damage.

Introduction

Oxidative stress is generally considered as one of the major factors leading to DNA damage. DNA damage induced by oxidative stress occurs primarily at three levels: the single/double strand level, the base/nucleotide level, and the DNA–protein crosslink level. Oxidative damages including lipid peroxidation and protein and DNA damage occur when oxidative stress caused by reactive oxygen species (ROS) exceed the antioxidation capacity of the organism [1], [2].

Exercise, especially that of long duration or high intensity, and its consequent tissue injuries are known to increase ROS production in mitochondria [3], [4]. Exercise can induce dehydration if lost fluid is not quickly replaced during exercise. Dehydration of 2% of body mass can impair physiological functions and exercise performance [5] by increasing heart rate and core temperature over time, decreasing cardiac output, and altering CNS function [6], [7]. In order to stabilize physiological conditions and minimize the stresses on cardiovascular, thermoregulatory and neuromuscular systems, it is important to replace fluids during exercise, thus prolonging exercising ability [8], [9].

Relationship between exercise performance, dehydration and rehydration has been demonstrated by many researches [10], [11]. However, no study to date has investigated the effect of hydration status on oxidative stress and subsequent DNA damage during exercise.

The purpose of this study was to determine the effect of dehydration and different types of fluid replacement on exercise performance, oxidative stress, and oxidative DNA damage during rest, exercise, and recovery.

Section snippets

Materials and methods

Subjects. Ten healthy and moderately active men between the ages of 21 and 29 years were recruited from Yonsei University. Subjects were injury- and disease-free as determined by a health history questionnaire and physical examination. All subjects provided informed consent, and the study protocol was approved by an institutional ethics review board in the department of physical education at Yonsei University.

Preliminary tests. VO2max during running was determined during a continuous, graded

Exercise time to exhaustion

The exercise time to exhaustion was significantly increased for groups C and S as compared to group D (p < 0.05). No significant differences were found among groups C, S and W (Table 1).

Plasma MDA and TAS levels

Plasma levels of MDA [MDA] and TAS [TAS] significantly increased from pre-dehydration to post-dehydration (p < 0.05) (Fig. 2A and B, respectively). Plasma [MDA] and [TAS] were significantly higher at exercise-15 min (p < 0.05), and at exercise-15 min and exercise-exhaustion (p < 0.05), respectively, as compared to those

Exercise time to exhaustion

It is well known that excessive dehydration prior to or during exercise impairs exercising ability as it negatively affects cardiovascular and thermal control systems [8], [10]. In our study, exercise time to exhaustion appeared to be significantly shorter in group D as compared to groups C and S. These results are in agreement with those of other recent studies [8], [11], [15], which demonstrated that a decrease in exercise performance were attributed to dehydration.

Carbohydrate

Acknowledgments

The authors thank the subjects for their time and effort during this study. We also thank the members of the exercise physiology, and food and nutrition laboratories at Yonsei University for their laboratory support throughout this study. We are especially grateful to Dr. Xiaocai Shi for his support. This study was supported by a grant from the Gatorade Sports Science Institute.

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