Introduction
Increasing evidence is highlighting the role antioxidants may have in protecting
against certain
conditions such as heart disease, stroke and cancers. It has been proposed that
the mechanisms leading to these diseases may be promoted by free radicals and that
antioxidants may oppose the action of these molecules. In addition to the well known
antioxidants such as Vitamins C and E, there
is
growing research demonstrating the
potentially beneficial effects of
plant-derived antioxidants, polyphenols, found in fruits, vegetables, nuts, cereals
and drinks such as tea and red wine.
Free radicals explained
Free radicals are unstable molecules that include the hydrogen atom, nitric oxide
(NO) and molecular oxygen (02). These naturally occur in the body as a result of
chemical reactions during normal cellular processes. They can also be formed in
response to excess pollution, too much UV sunlight and exposure to cigarette smoke.
In an attempt to stabilise, they attack other molecules in the body potentially
leading to cell damage and triggering the formation of
another free radical resulting in a chain reaction. Some scientists believe that
this type of free radical action has been implicated in certain chronic and ageing
diseases such as cancer, heart disease, stroke, rheumatoid arthritis, cataracts
and Alzheimers disease.
Protective mechanisms of antioxidants
Antioxidants are compounds that help to inhibit the many oxidation reactions caused
by free radicals thereby preventing or delaying damage to the cells and tissues.
Their mechanisms of action include:-
- Scavenging reactive oxygen and nitrogen free radical species
- Decreasing the localised oxygen concentration thereby reducing molecular oxygen's
oxidation potential
- Metabolising lipid peroxides to non-radical products
- Chelating metal ions to prevent the generation of free radicals
In this way antioxidants limit the free radical damage from:-
- Oxidising Low Density Lipoprotein (LDL) cholesterol, which may increase the risk
of athersclerosis
- Promoting platelet adhesion, which can lead to thrombosis thereby increasing the
risk of heart disease or stroke