Yet in the early 2000s, scientists trying to build on the theory encountered bewildering results: mice genetically engineered to overproduce free radicals lived just as long as normal mice, and those engineered to overproduce antioxidants didn't live any longer than normal. It was the first of an onslaught of negative data, which initially proved difficult to publish. The free-radical theory “was like some sort of creature we were trying to kill. We kept firing bullets into it, and it just wouldn't die,” says David Gems at University College London, who started to publish his own negative results in 2003 (ref. 6). Then, one study in humans showed that antioxidant supplements prevent the health-promoting effects of exercise, and another associated them with higher mortality.
None of those results has slowed the global antioxidant market, which ranges from food and beverages to livestock feed additives. It is projected to grow from US$2.1 billion in 2013 to $3.1 billion in 2020. “It's a massive racket,” says Gems. “The reason the notion of oxidation and ageing hangs around is because it is perpetuated by people making money out of it.”