Fig. 2.

The biological consequences of aging with respect to oxygen levels. In terms of aging, the truth is not a duality when it comes to the trade-off between hypoxia and hyperoxia, especially when issues such as oxidative stress and scavengers are involved. First, large deviations from normoxia (either increases or decreases in oxygen levels) generally lead to increased oxidative stress and reduced longevity. To the contrary, modest modulation of oxygen levels (either increases or decreases in oxygen levels) can enhance the antioxidant defenses and slow the aging process. These facts suggest both an alert threshold in hypoxia and a toxicity threshold in hyperoxia in the biological consequences of aging with respect to oxygen levels.