Application of Molecular Hydrogen as a Novel Antioxidant in Sports Science

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.