Hormesis is the process by which a little damage or stress to our biology can lead to a longer life span, as it wakes up the repair mechanisms and makes them do a better job than they otherwise would - a net gain in resiliency. Here is a review that summarizes the implications for much of mainstream research into aging and longevity: "Various nutritional, behavioral, and pharmacological interventions have been previously shown to extend life span in diverse model organisms, including Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, mice, and rats, as well as possibly monkeys and humans. This review aims to summarize published evidence that several longevity-promoting interventions may converge by causing an activation of mitochondrial oxygen consumption to promote increased formation of reactive oxygen species (ROS). These serve as molecular signals to exert downstream effects to ultimately induce endogenous defense mechanisms culminating in increased stress resistance and longevity, an adaptive response more specifically named mitochondrial hormesis or mitohormesis. Consistently, we here summarize findings that antioxidant supplements that prevent these ROS signals interfere with the health-promoting and life-span-extending capabilities of calorie restriction and physical exercise. Taken together and consistent with ample published evidence, the findings summarized here question Harman's Free Radical Theory of Aging and rather suggest that ROS act as essential signaling molecules to promote metabolic health and longevity." ROS can of course be acting both as useful signals and sources of damage in different circumstances - the fact that life can be extended by antioxidants specifically targeted to mitochondria, coupled with the evidence mentioned above, suggests that much.

Link: http://www.ncbi.nlm.nih.gov/pubmed/21619928