It also is unclear whether oxidative stress is a primary cause or a secondary phenomenon of chronic diseases, as well as of the aging process. In most human disease, oxidative stress is merely a symptom.

In fact, the amounts of antioxidants that lend protection are not known and probably differ among individuals. People exposed to increased oxidative stress may have elevated antioxidant requirements.

The main role of antioxidants is to prevent oxidative damage to cellular components, so it has been proposed that dietary antioxidants decrease such damage and with it the risk of disease. This has stimulated interest in the possible preventive potential of antioxidant supplements.