Oxidation would also increase the peroxide value, which is itself an active pro-oxidant.

When and how this antioxidant becomes a pro-oxidant.

"It's a redox agent - an antioxidant in some circumstances and a pro-oxidant in others."

Iron is a pro-oxidant.

Or maybe beta carotene works as an antioxidant only in concert with some other plant chemical or process; under other circumstances, it may behave as a pro-oxidant.

A decreased molecular weight or a decrease in the degree of polymerization of ocular melanin has been proposed to turn the normally anti-oxidant polymer into a pro-oxidant.

This activates the transcription of pro-inflammatory cytokines (Tumor necrosis factor-alpha or TNFα) and production of superoxides (a pro-oxidant).

Bush thinks that AP could be just like SOD1: a protective antioxidant when properly loaded with copper and zinc, but a dangerous pro-oxidant when zinc is lacking.

Myricetin may also act as a pro-oxidant in its ability to increase the production of hydroxy radicals through reactions with Fe or Fe EDTA and hydrogen peroxide.

Iron is a powerful pro-oxidant that might do damage in excess, and a high level of iron in complementary foods has been shown to interfere with the absorption of other minerals (zinc and copper)(7).

One of those cautious experts, Dr. Victor Herbert, a professor of medicine at the Mount Sinai School of Medicine in New York, warned that the vitamin supplements could actually be harmful, because beta carotene acts as a pro-oxidant in some circumstances.