Toxicity of Antioxidants

Bashir M. Rezk*, Wim J. F. van der Vijgh, Aalt Bast and Guido R. M. M. Haenen

Toxicity of Antioxidants.

The beneficial effects of antioxidants are due to their ability to protect against free radical damage. In the diseases and other pathological conditions where free radicals are implicated, the biochemistry may greatly vary, i.e. the radicals involved, their flux, the site where they are generated and the target they attack can differ.1 Thus for each type of radical damage specific criteria need to be fulfilled by an antioxidant in order to be active.

Reactive Oxygen Species (ROS) is a collective term that includes both oxygen centred radicals and
certain oxygen containing non-radicals that are oxidizing agents or easily converted into radicals. The adjective “reactive” is not always appropriate; H2O2, O2•- and NO• quickly react only with very few molecules. OH• reacts instantaneously with almost everything. RO2•,RO•, HOCl, NO2•,ONOOH, and O3 have a reactivity that lies in between these extremes.

Regarding safety, in the 16th century Paracelsus already stated that all compounds are toxic, provided the dose is high enough.  On the contrary, the mega-dosages sometimes recommended make safety a very relevant issue for antioxidants. The biological origin of most antioxidants helps to increase the acceptance of antioxidant supplementation by the general public.

An important issue in the use of antioxidants is metabolism.4 Like other bioactive compounds, metabolites formed by phase 1 and phase 2 enzymes can contribute to the beneficial and toxic effect of an antioxidant. Unintentional and intentional exposures continue to be a significant cause of morbidity and mortality in the United States. It is of importance to identify groups that are at risk.


Toxicol Forensic Med Open J. 2015; 1(1): e3-e4. doi: 10.17140/TFMOJ-1-e002