[danarlow]

Many plant-derived chemicals that are called "antioxidants" by the popular press (e.g. catechins [1], anthocyanins [2], retinoids [3], etc.) have been shown to kill some types of cancer cells in vitro and in animal models, but not because they function as antioxidants per se. Instead, it seems that they modulate particular cell signalling pathways that regulate cell growth and survival just like other targeted cancer drugs [4]. In other words, the fact that these molecules can neutralize free radicals in vitro is irrelevant to their mechanism of action. Treating all of these diverse chemicals as one class, "antioxidants", just muddies the waters.

In fact, there are even some cases where an "antioxidant" molecule selectively killed a type of cancer cell by increasing oxidative stress inside cells, the opposite of what you'd expect from the blanket label. For example, it was recently shown that high doses of vitamin C selectively kill a type of colorectal cancer cell, but the mechanism of action was actually that the cells take up the oxidized form of vitamin C via a sugar transporter that tends to be upregulated in cancer cells, and the vitamin C-derrived pro-oxidant caused an oxidative stress signalling cascade that led to cell death [5].

[1] https://en.wikipedia.org/wiki/Catechin

[2] https://en.wikipedia.org/wiki/Anthocyanin

[3] https://en.wikipedia.org/wiki/Retinoid

[4] A corollary is that, like other drugs, each of these chemicals that is effective against some type of cancer probably won't necessarily work against other types.

[5] http://science.sciencemag.org/content/early/2015/11/04/scien...