The Influence of Melatonin Supplementation in the Group of Persons Performing Competitive Sport.

Athlete's body, by its high oxygen demand and increased aerobic metabolism, is exposed to the formation and oxidizing action of reactive oxygen species (ROS). Imbalance between the mechanisms of ROS generation and antioxidative defense of the body can lead to oxidative stress expressed by elevated concentrations of lipid peroxidation products, such as malondialdehyde, isoprostanes (8-iso-PGF2α), oxidized low-density lipoprotein molecules (ox-LDL). The body's defense against ROS includes two systems: nonenzymatic and enzymatic. Small-molecule antioxidants include reduced glutathione (GSH). Due to the presence of -SH groups, glutathione has strong reductive properties. The compound is a substrate for glutathione peroxidase (GSH-Px) which decomposes hydrogen peroxide and organic peroxides. Among antioxidant enzymes are also: superoxide dismutase (Cu-Zn-SOD, scavenges superoxide anion radical), catalase (CAT, reduces hydrogen peroxide), and glutathione reductase (GR, reduces oxidized glutathione). Another well-known small-molecule antioxidant is melatonin, hormone of the pineal gland. It has been demonstrated that this compound can reduce hydrogen peroxide, scavenge hydroxyl radical and deactivate nitric oxide radical.

Another manifestation of disruption of homeostasis in the body of a professional athlete are enhanced inflammatory processes. This can be explained by the fact that during physical effort of varied intensity, increased activity of myeloperoxidase and higher levels of mRNA for tumor necrosis factor, interleukin-1 and -6 are observed. Interleukin-6, also known as myokine, is a particularly important marker of intense physical effort released from damaged muscles. Myokine is also the main upregulator of the synthesis of C-reactive protein (CRP) in the liver, hence measuring the concentration of the protein can indicate the intensity of inflammatory processes in an athlete's body. It has been demonstrated that melatonin, in addition to its hormonal and antioxidant properties, can modulate inflammatory processes by reducing the synthesis of proinflammatory cytokines.

Taking into account the multidirectional function of melatonin, it seems interesting to establish the impact of 30-day supplementation of this hormone on the antioxidative defense mechanisms and the release of markers of oxidative stress and inflammation in rowers and footballers undergoing training of submaximal intensity.