The flavanoid antioxidants are largely secondary metabolites synthesised by plants to deter herbivorous predators, repel competitors and attract pollinators. Humans have “managed” secondary metabolites such as nicotine, have succumbed to others, such as atropine (in deadly nightshade), exploited many, as medicines e.g. digoxin, and enjoyed the colours and perfumes, flavours and aromas, of the large number of them present in foods, flowers and medicines. The better known antioxidants are some of the mineral elements e.g. selenium and vitamins A, C and E which play important cooperative roles, and polyphenols and carotenoids.
Grouped together as antioxidants (which in in vitro experiments they are) these compounds are thought to be therapeutic to humans ingesting them in diets rich in fruits and vegetables. Read more ....

It has been observed in in vitro experiments that they can neutralise damaging free radicals, the by-products of necessary energy generating processes that, if left in body cells in excess, cause oxidative stress, a precursor of ill-health.
in vivo studies are slowly building a picture of the efficacy of food-based natural antioxidants (FBNA) in support of epidemiological surveys that for many years have linked diets rich in antioxidants (e.g. the mediterranean diet) with good health and lower levels of degenerative diseases and longer life. Scientists are curious about the mechanisms involved in this process. Read more ...

For food-based compounds to be therapeutic antioxidants they have to:-
1. Exhibit in vitro antioxidant activity (capacity).
2. Be absorbed from the gut into the blood stream.
3. Be able to accumulate at the target (tissue or organ) site, or to trigger the production of secondary endogenous antioxidants, e.g. enzymes, etc. that can.
4. Reduce oxidative stress.
5. Be efficacious.
"Stars" (1-5 based on the above requirements) have been awarded to scientific studies evaluated here, depending upon the depth of the enquiry. 1 star has been awarded to a great many studies of FBNA isolated and tested in the lab, 2 stars can be awarded to many trials reporting the absorption of single compounds raising the antioxidant capacity of blood plasma. 3 stars have been awarded to relatively few experiments demonstrating the antioxidant present in increased amounts at the target site soon after administration. 4 and 5 star demonstrations await further research. Read more ....

So far there is little evidence that antioxidant supplements have any effect. Browse among the links to explore some examples of the current experiments and hypotheses to determine the possible roles of food-based natural antioxidants in human nutrition, health and well-being.
Because there is only epidemiological evidence that antioxidants are the active agents in the process of oxidative stress reduction, a page on alternative theories has been included. Although at this time (April 2009) there is a lack of analytical methodology to support the hypothesis of hormesis, the idea is most appealing in the search for mechanisms to explain the experimental evidence being gathered on how food-based antioxidants work. Read more ...