The scientific consensus these days is that ingesting antioxidants in the hope of improving your metabolism isn't going to work.
Since the early 1990s scientists have been putting these compounds through their paces, using double-blind randomised controlled trials - the gold standard for medical intervention studies. Time and again, however, the supplements failed to pass the test. True, they knock the wind out of free radicals in a test tube. But once inside the human body, they seem strangely powerless. Not only are they bad at preventing oxidative damage, they can even make things worse. Many scientists are now concluding that, at best, they are a waste of time and money. At worst they could be harmful.
It is, however, quite true that the antioxidants generated by your own biochemistry are important in health and longevity. Some of the difference in longevity between species is ascribed to the degree to which they manufacture their own antioxidants:
It's reasonable to theorize that if you happen to be a member of a species that naturally generates a lot of antioxidants around the mitochondria, you're going to live longer than members of another, similar species with worse luck in the antioxidant stakes.
The key here appears to be where the antioxidants end up performing their work. Mouse studies have shown that carefully directing antioxidants to the cellular mitochondria extends healthy life span on the order of 20-30% - a fairly complex feat of biochemical engineering that no presently available pill can match. Those studies further showed that no benefit emerges from the same antioxidants sent elsewhere in mouse biochemistry. If you'd like to learn more about why antioxidants in the mitochondria make such a large different, head back into the archives for an outline of the Mitochondrial Free Radical Theory of Aging: mitochondria create free radicals that cause all sorts of damage, but targeted antioxidants can soak up some portion of the free radicals before that damage occurs.
Our biology is complex - why would we expect that successfully modifying it with chemicals would be as simple as eating those chemicals? Ingesting antioxidants in the hope of benefit because they happen to do certain things in certain portions of your biochemistry is magical thinking given the evidence on the table to date. It certainly doesn't have the best record in experimental studies. Here's one of the latest:
First the good news: a study by scientists at the Buck Institute for Age Research shows four common antioxidants extended lifespan in the nematode worm C. elegans. And the not such good news: those four were among 40 antioxidants tested, the majority of which did nothing or caused harm to the microscopic worms.
“We’ve taken a careful look at the way antioxidants affect aging in simple animals and what we find is that it’s a hodge-podge of effects,” said Buck Faculty member Gordon Lithgow, PhD, lead author of the study. “We see antioxidants that appear to make simple invertebrates live healthier, longer lives and we also find antioxidants that have precisely the opposite effect, that compromise the animal’s survival,” he said.
"I’m an optimist, I think we can make positive statements about the potential for intervening in aging with compounds that manage oxidative stress,” said Lithgow. “I’m also saying that we’re not there yet, and if only four of the 40 compounds are having the desired effect, that’s not good when we think about applying these results to humans today.”