Effects Of Vitamin E (Palm Vitee) Supplementation On Exercise-Induced Lipid Peroxidation And Endurance Performance In The Heat

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Date
2005-01
Authors
CHEE KEONG
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Abstract
The increase in oxygen consumption during endurance exercise leads to free radical (FR) production and subsequent lipid peroxidation (LlPOX). Raised body temperature has also been reported to increase the rate of FR production. This oxidative stress may impair endurance performance since FRs can cause cell damage and has been implicated in muscular fatigue. Vitamin E supplementation has been shown to attenuate FR-induced LlPOX. It is however unclear if vitamin E supplementation could decrease LlPOX and improve endurance running performance of heat-adapted recreational athletes in the heat. PURPOSE: The first phase of this study examined the effects of exercise in the heat (H) and thermoneutral (N) environments on endurance running performance and exerciseinduced LlPOX while the second phase investigated the effects of vitamin E (Palm Vitee) supplementation on exercise-induced L1POX and endurance performance in the heat. METHODS: First phase - 17 healthy, male recreational athletes (aged: 25.8 ± 1.8 yrs; body weight: 59.1 ± 1.6 kg; V02max: 57.6 ± 1.8 mL.kg-1.min-1 ) completed two endurance running trials until exhaustion on a motorised treadmill at - 70% of V02max at environmental temperatures of 31°C (H) and 25°C (N) with a relative humidity (RH) of - 70% on two separate occasions. Second phase - 18 healthy, male recreational athletes (aged: 24.9 ± 1.4 yrs; body weight: 59.6 ± 1.5 kg; V02max: 57.7 ± 1.5 mL.kg-1 min-1 ) completed two endurance running trials until exhaustion on a motorised treadmill at 70% V02max on two separate occasions following a 6-week supplementation of either vitamin E (E) or placebo (P). Both trials were conducted at an ambient temperature of 31°C and a 70% RH. During the trials, rectal temperature (Tree), skin temperature (Tsk) , heart rate (HR) and ratings of perceived exertion (RPE) were recorded at 10-min intervals while oxygen uptake (V02) was recorded every 20 min. Blood samples were collected every 20 min during the running trials for the determination of plasma volume changes (PVC), lactate (LAC), glucose (GLU), free fatty acid (FFA), triglyceride (TRI), malondialdehyde (MDA), creatine kinase (CK), total antioxidant status (TAS), cholesterol and vitamin E. RESULTS: First phase - Compared to the N trial, time to exhaustion was significantly (p<0.001) shorter in the H trial (68.8 ± 3.1 vs 91.8 ± 4.3 min). Tree, Tsk , mean exercise HR, RPE, during the course of the trial were significantly higher in the H trial. Tree at exhaustion was significantly higher in the H trial than in the N trial (39.3 ± 0.1°C vs 38.8 ± 0.1°C; p<0.001). Plasma volume reductions, GLU, LAC and FFA concentrations, particularly towards the latter half of the trials, were significantly higher in the H trial (p<0.01). No significant differences in V02, TRI and TAS were observed between trials. Plasma MDA was significantly higher (p<0.05) at exhaustion compared to the resting level in the H trial but this significance was lost when the data were adjusted for changes in plasma volume. Plasma CK activity only increased slightly at exhaustion in both the trials but no statistically significant difference was evident between the two trials. However, at 24 h post-exercise, CK activity was significantly (p<0.01) higher than the resting values in both the trials. Second phase - No significant differences were evident in Tree, Tsk, HR, RPE, V02 or in the time to exhaustion between the E and P trials (81.1 ± 4.5 vs 76.9 ± 4.5 min respectively). Similarly, PVC, CK, LAC, GLU, FFA, TRI and TAS were also not different between the two trials. Vitamin E supplementation, however, resulted in a significantly higher (p<0.001) mean serum vitamin E concentration at rest and during post-exercise compared to that in the placebo trial. Resting plasma MDA concentration in the E trial was significantly lower than that in the P trial (0.38 vs 0.46 J.lmoI.L-1 ; p<0.05). At exhaustion, plasma MDA was higher than the resting values in both trials and it was higher in the P trial compared to the E trial although the difference did not reach statistical significance (p=O.090). CK activity at exhaustion, 1 hand 24 h post-exercise was not different during the two trials but was significantly higher (p<O.001) than the corresponding resting values in both trials. CONCLUSION: These results reveal that for a given workload there was a greater thermoregulatory stress in the H trial. Endurance performance in heat (31°C) was reduced by 25% when compared to performance in a thermoneutral environment (25°C). As the levels of plasma MDA increased at exhaustion compared to the corresponding resting values in both trials, there was a possibility that FRs could have contributed to fatigue at the end of both endurance running trials in the first phase. However, as the levels of MDA was not significantly different between trials, the role of FRs during endurance exercise in the heat and fatigue remains unclear and need further investigation. Vitamin E supplementation decreased lipid peroxidation at rest and, to some extent, during exercise in the heat as evident from the lower MDA levels. It however, does not enhance endurance running performance or prevent exercise-induced muscle damage during exercise in the heat. In addition, vitamin E supplementation did not influence the changes of some of the physiological parameters (e.g. PVC, LAC, GLU, FFA, TRI, CK and TAS) that occurred during exercise in the heat.
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Effects Of Vitamin E (Palm Vitee) Supplementation On Exercise-Induced Lipid Peroxidation , And Endurance Performance In The Heat
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