Hydrogen is considered generally recognized as safe (GRAS) by FDA: GRAS Notice Number 520, Hydrogen Gas; For use as an ingredient in drinking water, flavored beverages, and soda drinks at a level up to 2.14% by volume.
Oxidation and reduction(anti-oxidation) are ongoing processes happening in our body. Increasing levels of Hydroxyl free radical type of oxidative stress can cause damages to our healthy cells and eventually our DNAs. Molecular Hydrogen selectively neutralises with these free radicals to convert them into water.