The basis of the observation that oxidative stress is hard on cells comes from the observation that many cell lines fail to grow in standard conditions (20 C, a

The basis of the observation that oxidative stress is hard on cells comes from the observation that many cell lines fail to grow in standard conditions (20 C, atmospheric pressure, normal atmosphere), and that the oxygen tension in most tissues is actually well below atmospheric. These same cell lines survive when incubated in low oxygen conditions. This sort of difference, 21% [O2] vs 3% [O2] is massive to a biologic system, but observable results show up in hours to days. The idea was that, over a lifetime, similar oxidative stress, at far lower levels, would necessarily build up in cells over a lifetime. However, certain disease conditions, like G6PD deficiency, give us a window into human physiology with limited antioxidant capacity and a moderately sized study in Sardinia has shown they may actually have a somewhat lower cancer risk overall. Antioxidants fall into the giant pool of "meh" for most issues.