Why do we need antioxidants?
Oxidation is a natural process that occurs in all living organisms. Breathing, metabolism and cell respiration produce free radicals, but also illness, injury or intensive exercise (humans only!).
Free radicals are also produced by external factors such as pollution, cigarette smoke, sun (UV) exposure, pesticides and other chemicals.
At moderate concentrations free radicals play an important role in a number of biological processes, such as smooth muscle relaxation or cellular signaling processes. They can even be produced on purpose by the immune system to kill bacteria or the damaged cells.
Free radicals are very unstable because they have lost at least one electron in the reaction. To regain their stability, they must react quickly with the nearest compounds to capture the missing electron. When the other molecule loses its electron, it becomes in turn a free radical and a chain reaction can begin.
What do antioxidants do?
Plants, animals and humans have developed their own defense systems against oxidation and synthesize powerful molecules called antioxidants. Animals and humans cannot synthesize all the antioxidants they need and must acquire them from plant foods.
Antioxidants stop the chain reactions by removing free radical intermediates, and inhibiting other oxidation reactions. In the ideal situation, there is a balance between free radical production and the defense mechanism.
If the free-radical production becomes excessive, or if there is a lack of antioxidants, oxidative stress occurs damaging of lipids, proteins and DNA , and can even cause cell death.
Free radical accumulation is involved in the development of several disorders such as cardiovascular disease, cancer, diabetes, and is associated with ageing.
Where do we find antioxidants?
Vitamins C and E are the best known; they are found in fruits, vegetables and oils for vitamin E. They work in team with vitamin A and regenerate each other.
Many carotenoids are also antioxidants, like beta-carotene (precursor of vitamin A) found in carrots or dark green salads, and lycopene found in tomatoes or watermelons.
Polyphenols are also a large class of antioxidants, such as the isoflavones from soy or the anthocyanins that give the purple colour to blueberries.
Did you know that plants use carotenoids or polyphenols as “sun-blockers” to protect themselves from oxidation by the sun and burning?
There are recommended daily amounts for vitamins but not for other antioxidants. Generally a diet rich in grains, fruits and vegetables provides the recommended amount of antioxidant vitamins and plenty of other antioxidant compounds. It is therefore best to stick to dietary sources and if vitamin supplements are really needed, do not overdose, because in this case more is not better. Too much antioxidant can become pro-oxidant and have reverse effect.
ILSI EUROPE CONCISE MONOGRAPH SERIES. OXIDANTS, ANTIOXIDANTS, AND DISEASE PREVENTION 1995
Free radicals in the physiological control of cell function. W. Dröge Physiological Reviews 2002, 82:47-95