The topic of hydrogen, whether delivered as hydrogen water or hydrogen inhalation, acting as an "antioxidant" is something I have addressed numerous times before. Despite myself and many others trying to correct misinformation and misconceptions, the claims of hydrogen water being an antioxidant remain pervasive. One of the most common claims is that "hydrogen water is the most powerful antioxidant known". This is demonstrably false, and the early beliefs that hydrogen gas works asa direct free radical scavenger relied on in vitro studies (cell studies done outside the body) showing it to selectively reduce the most damaging stressors, largely as it is an incredibly WEAK antioxidant.
Hydrogen water may show to selectively reduce the nastiest oxidative and nitrosative stressors in vitro, but in vivo (in the living body) the chance of this happening is highly unlikely. If it does happen, it most likely will only have a negligible impact. In fact, in some studies, molecular hydrogen has actually shown to increase oxidative stress¹. Far more profoundly, molecular hydrogen has shown evidence of promoting the function of our redox homeostasis²,³,⁴; the delicate balance between antioxidants and oxidative stress. Hydrogen water does not work as a direct antioxidant, and this is a good thing. Antioxidant supplementation has shown to lack efficacy at best in a recent meta analysis⁵, and in some cases, may prove harmful due to indiscriminately reducing necessary oxidative species and down regulating our endogenous production of antioxidants⁶, even leading to an increase in prevalence of cancer⁷.
Molecular hydrogen works as an antioxidant in vivo by activating the Nrf2, pathway, regulating our body's endogenous antioxidant production of glutathione, catalase, and super oxide dismutase, and promoting a homeostatic antioxidant/oxidative stress balance ⁹,¹⁰,¹¹,¹²,¹³. There are several "Nrf2" activators on the market. However, disturbing evidence suggests in some instances, Nrf2 activation beyond homeostatic levels can promote tumor growth and decrease the effectiveness of chemotherapy gives pause for caution ¹⁴,¹⁵. The evidence on molecular hydrogen suggests this is not a concern. In fact, molecular hydrogen has evidence for both suppression of tumor growth¹⁶,¹⁷,¹⁸, while mitigating the negative has evidence side effects of cancer treatments without interfering with efficacy, perhaps even potentiating efficacy, in two randomized clinical trials as well as rodent studies¹⁹,²⁰,²¹,²²,²³. It may even improve the prognosis for cancer patients, according to one recent human study²⁴, although much more research is needed for any definitive statements.
In the last several years, it has become more and more clear that the reason high doses of indiscriminate antioxidants are not beneficial for most people, but potentially harmful, could be due to many oxidative compounds functioning as signaling molecules. Nitric oxide (NO), for instance, is a free radical that can cause oxidative stress. However, we know that it has a critical role in our health, particularly in vasodilation, with work done to demonstrate this leading to the 1998 Nobel Prize in Physiology or Medicine²⁵.
Hydrogen may play a role not just in regulating our endogenous antioxidants, but also with "good" reactive oxidative species. Hydrogen has been shown to regulate NO in the hippocampus through regulating the enzyme neuronal nitric oxide synthase (nNOS)²⁶. In addition, by diminishing inducible NOS (iNOS) expression and decreasing NO levels, hydrogen can inhibit a type I allergy response²⁷. While hydrogen increases iNOS activity in an animal model of liver inflammation²⁸, it can simultaneously protect against the effects of elevated NO levels leading to the nitrogen radical peroxynitrite by neutralizing ONOO while bypassing NO²⁹. Hydrogen has also been shown to protect against nitrosative stress along with oxidative stress³⁰. Additionally, while hydrogen water does not directly scavenge hydrogen peroxide (H₂O₂) another "good" reactive oxidative species that has beneficial physiological roles, it has show to indirectly suppress excess hydrogen peroxide levels³¹.
Basically, we need some amounts of the "good" oxidative species in our system and also need the right amount of antioxidants, Too much or too little of either is a bad thing. We have previously put out a simplified video explaining this, here. This is why we will use terms such as "antioxidant-like effect" or "combats excess oxidative stress," but do not refer to molecular hydrogen as an antioxidant; at least not in the context of inside the body.