Acute sport exercise leads to a strong stimulation of muscle tissue and a change 
in the organism energy demands. This study was designed to investigate the 
effect of oral melatonin supplementation on human physiological functions 
associated with acute exercise. Immune, endocrine and metabolic parameters were 
measured in 16 young male football players, who were divided into two groups, an 
experimental group (supplementation with 6 mg of melatonin administered 30 min 
prior to exercise) and a control group (placebo without melatonin). They 
performed a continuous exercise of high intensity (135 beats/min). Samples were 
collected 30 min before the exercise and 3, 15 and 60 min during the exercise. 
The results indicated that the acute sport training presented: a) increased 
lipid peroxidation products (MDA) in both groups, control and experimental, with 
levels significantly decreased in the group treated with melatonin after 15 and 
60 min of high-intensity exercise, b) the total antioxidant activity (TAS) was 
lower in the control group than in the experimental, the latter showing 
significant differences at 60 min of high-intensity exercise c) the lipid 
profile of subjects in the experimental group showed lower triglyceride levels 
than the control group after 15 and 60 min of high-intensity exercise, d) 
immunological studies only showed, in the experimental group, an increase in IgA 
levels at 60 min after the exercise, and finally there were no significant 
differences between the groups for any of the other variables. In conclusion 
these results indicated that treatment with melatonin in acute sports exercise 
reversed oxidative stress, improved defenses and lipid metabolism, which would 
result in an improvement in fitness.