An antioxidant can be described in simple terms as
anything that can delay or prevent oxidation of a
susceptible substrate. Our antioxidant system is
complex, however, and consists of various intracellular
and extracellular, endogenous and exogenous,and aqueous and lipid-soluble components that act
in concert to prevent ROS formation (preventative
antioxidants), destroy or inactivate ROS that are
formed (scavenging and enzymatic antioxidants),
and terminate chains of ROS-initiated peroxidation
of biological substrates (chain-breaking antioxidants).
In addition, metals and minerals (such as
selenium, copper, and zinc) that are key components
of antioxidant enzymes are often referred to as
There are many biological and dietary constituents
that show ‘antioxidant’ properties in vitro. For
an antioxidant to have a physiological role, however,
certain criteria must be met.
1. The antioxidant must be able to react with ROS
found at the site(s) in the body where the putative
antioxidant is found.
2. Upon interacting with a ROS, the putative antioxidant
must not be transformed into a more
reactive species than the original ROS.
3. The antioxidant must be found in sufficient
quantity at the site of its presumed action in
vivo for it to make an appreciable contribution
to defense at that site: if its concentration is
very low, there must be some way of continuously
recycling or resupplying the putative