At the blog Fight Aging!, Reason draws attention to the possibility that taking large amounts of antioxidant supplements may not necessarily be an improvement:

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.

And as the author points out, and contrary to popular perception, free radicals play positive roles in the human body as well. A similar point was made by critical care researcher and cryonics activist, Dr. Steve Harris on usenet in 2002:

Free radicals are the signals used by the body’s inflammatory system, which is necessary for infection-fighting, normal healing, and for fighting some (not all) kinds of cancer.  Free radicals (including deliberately produced ones like NO) aren’t just garbage to be expunged in every possible way you can think of, but rather instead are often important signals, not to be ignored. You can’t just willy-nilly shotgun them, and the system which uses them, out of existence for long, without expecting to pay a price. Nature didn’t give it all of that complicated radical-producing and radical-sensing machinery to you, for nothing.

Dr. Harris himself observed the price that may be paid when he participated in the Critical Care Research canine cerebral resuscitation experiments:

I’ve given large doses of vitamin E, melatonin, PBN, NOS inhibitors, COX inhibitors, basically the anti-radical anti-inflammation works, to dogs in resuscitation trials. This works great on the brain but occasionally I see a dog get pneumonia, and some of them die from it, with complete lung consolidation, in as little as 12-24 hours, despite heavy IV antibiotics. And in a very odd way: no fever, no left-shifted neutrophils, no increased heart rate, no shock (except at the hypoxic end). The last time I saw anything like that as a physician was treating leukemic patients with no neutrophils. These dogs have neutrophils, but they’re just not working.

Aggressive antioxidant treatment has a place in the treatment of stroke and cardiac arrest but to implement such an aggressive regime in the hope of fighting aging may be wishful thinking at best, and dangerous at worst. In general, many claims about the beneficial effects of dietary supplements should be approached with skepticism.

Any credible future treatment to slow or reverse aging will require interventions that specifically target the mechanisms of aging and/or remove their damaging effects without disturbing the general biochemistry of the human body. Whether such interventions will be possible without advanced nanomedical modification of human biology remains to be seen.