An Exploration of the Direct Biological Targets of Molecular Hydrogen

Molecular hydrogen (H2), supplied either as a gas or in a solution, has been gaining popularity as a treatment for a variety of conditions and diseases. For example, it has been suggested to be beneficial for neurodegenerative diseases, to ease the injuries caused by restoration of blood flow to previously ischaemic tissues, and even to alleviate the symptoms of COVID-19. It has also been suggested as an ergogenic sports supplement. However, the exact mode of action of H2 has yet to be definitively unravelled. It has been suggested that H2 acts as an antioxidant and, in particular, as a scavenger of hydroxyl radicals (·OH). This might be the case, but it is unlikely that this is the only mode of action of H2 in biological systems. Here we discuss some of the possible mechanisms by which H2 may have an effect, which may explain how it is acting in a medical context.