Molecular hydrogen (H2) is a colorless, tasteless, odorless, and minimal molecule with high flammability. Although H2 has been thought to be an inert gas in living bodies for many years, an animal study reported that inhalation of H2 gas decreased oxidative stress and suppressed brain injury caused by ischemia and reperfusion injury due to its antioxidant action. Since then, the antioxidant action of H2 has attracted considerable attention and many studies have reported on its benefits. Most studies have reported the effects of H2 on diseases such as cancer, diabetes, cerebral infarction, and Alzheimer's disease. However, little is known regarding its effects on healthy subjects and exercise. Thus far, including our study, only 6 studies have explored the effect of H2 on exercise. H2 is the smallest molecule and therefore can easily penetrate the cellular membrane and rapidly diffuse into organelles. H2 is thought to be able to selectively reduce hydroxyl radicals and peroxynitrite and does not affect physiologically reactive species. H2 can be supplied to the body through multiple routes of administration, such as oral intake of H2 water and H2 bathing. Therefore, H2 may be a potential alternative strategy for conventional exogenous antioxidant interventions in sports science. The purpose of this review is to provide evidence regarding the effects of H2 intake on changes in physiological and biochemical parameters, centering on exercise-induced oxidative stress, for each intake method. Furthermore, this review highlights possible future directions in this area of research.
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