Borrowed Time: The Science of How and Why We Age

by Sue Armstrong

He supported his hypothesis by demonstrating that he could increase the lifespan of laboratory mice by up to 30 per cent by giving them drugs to protect them against radiation. He could also increase their lifespan, but not so dramatically, by giving them antioxidants designed to prevent oxidative damage. The relative weakness of antioxidant therapy perplexed Harman for a long time and led him eventually to conclude that most free radicals are generated inside the mitochondria, the cell's batteries, which burn calories to produce our energy and which are impenetrable to compounds introduced from outside. In the 1970s he modified his theory to suggest that the mitochondria might be the body's clock, determining how long we live according to how hard we work our batteries and how much wear and tear they sustain.