Antioxidants are chemicals that interfere with oxidation – the process where an atom or molecule loses some electrons due to a chemical reaction.
In the context of a healthy diet, antioxidants are substances found in food items which help shield biological molecules such as DNA from this potentially destructive activity. These substances include vitamins like vitamin C and vitamin E, trace elements such as selenium and zinc, and other common plant compounds such as lycopene and flavonoids.
A diet that includes a reasonable mix of fruit, nuts, vegetables, and mushrooms should contain sufficient antioxidants to guard our cellular machinery against oxidative stress.
How does oxidation harm our bodies?
Oxidative damage occurs when an electron is stolen from an important biochemical structure, such as a base in a genetic code or the amino acids making up proteins.
Simple changes to DNA can transform a base into something different, altering its behavior so it no longer spells out the same sequence. Changing parts of a protein might make them less likely to break down, potentially allowing them to accumulate into toxic clumps. Oxidation of the fats making up the membranes of cells can make them less flexible, shortening their lifetime or making them less adept at performing their job.
While our bodies have repair mechanisms that can account for these damaging changes, as we age the problems can pile up. Mutations get missed, aggregations of proteins build, and risks of diseases like cancer or even neurodegenerative conditions like Parkinson's increase.
Even in best-case scenarios, oxidative stress might contribute significantly to the aging processes we all take for granted. Graying hair and wrinkles might be impossible to avoid, but may not be helped by chemical processes that sweep in and steal a few electrons here and there.
What causes oxidative stress?
Our bodies naturally produce a range of chemical products called free radicals as a consequence of typical metabolic processes. These include reactive oxygen species such as hydrogen peroxide, which is both destructive and – under some circumstances – a useful signalling molecule.
To deal with these reactive species, our bodies also produce enzymes with antioxidant properties, like superoxide dismutase. Such enzymes keep the free radicals we produce in check, either by quickly replacing lost electrons or mopping up radicals before they can cause damage.
But our environment can also be a source of free radicals. Absorbing pollutants, including cigarette smoke and toxic metals, can overwhelm our bodies' home-grown defenses and increase oxidative damage.
Do you need antioxidant supplements?
Between our own enzymes and the antioxidants we collect in our diet, our body is as well prepared for keeping a lid on oxidative stress as it can be.
Unfortunately, adding more antioxidants to the mix isn't the solution we might imagine. For one thing, providing more electron donors isn't going to necessarily rebalance electron thefts. More importantly, studies over the decades have found no sign that antioxidant supplements can reduce risks of ill health or combat aging.
If anything, evidence points in the other direction. A 2007 metastudy on randomized trials found a slight increase in mortality among groups who dosed up on antioxidant supplements.
Further research is needed to figure out why supplementary antioxidants don't seem to reduce oxidative stress in the body and what possibly can.