VITAMIN C - THE MASTER NUTRIENT
Preface | Foreword | Introduction | Chapter 1 | Chapter 2 | Chapter 3 | Chapter 4 | Chapter 5 | Chapter 6 | Chapter 7 | Chapter 8 | Chapter 9 | Chapter 10 | Chapter 11 | Chapter 12 | Chapter 13 | Bibliography
Vitamin C Scavenges Poisonous Free Radicals
It is astonishing how long the list has become of substances toxic to health. Even apart from the environmentally derived poisons including lead from auto emissions, pesticides, nitrates, ozone, radioactive exposure, mercury from dental fillings, PCB's, etc., it is also true that many natural processes and substances vital to life and health can also do us in. Including, amazingly, oxygen, the breath of life.
In the words of Etsuo Niki, contributing scientist from University of Tokyo at the recently held NY Academy of Science Conference on Vitamin C(161), "oxygen is a double-edged sword. We cannot live without oxygen, but at the same time we are continuously exposed to oxygen toxicity......the free radical mediated peroxidation of biological molecules and tissues have received much attention in connection with a variety of pathological events such as heart disease, rheumatoid arthritis, inflammatory disorders, cancer and even the aging process". This is the introduction to Niki's elegant research paper describing the synergistic action of Vitamins C and E in combating toxic oxygen species.
What then are "free radicals" and "toxic oxygen species"? Why are they so dangerous? And what is Vitamin C's role in neutralizing and destroying these toxic species?
Free radical oxygen species, some of which are toxic, are highly reactive, unstable molecules because they have lost an electron. Examples include hydrogen peroxide, superoxide, hydroxyl radical and singlet oxygen. In the chemical drive to replace that missing electron, free radicals may initiate an entire cascade of chemical reactions, resulting in damage to membranes, DNA mutations, accelerated ageing, disruptions in cell vitality and function, and deposition of fat. Reactant oxidant species are thought to underlie the cause of many diseases; the use of natural anti-oxidants is widely advocated in the treatment and detoxification from such conditions(101).
Contrary to what one might think, free radicals are not always externally derived; they occur and are generated in the body's natural biochemical course of living and metabolism, through the oxidation of polyunsaturated fats, the increased generation of adrenalin and noradrenalin under stress, and even as toxic weapons used by phagocytes, some of the foot soldiers of the immune system. External sources of free radicals include exposure to low levels of nuclear radiation and electromagnetic emissions, smog with its powerful oxidants such as ozone, nitrogen dioxide, and peroxyacyl nitrates, cigarette smoke, and environmental pollutant drugs and chemicals(65).
Reassuringly, however, there are a number of natural substances, including Vitamin C, which are powerful anti-oxidants and free radical scavengers, and which act to prevent the damaging effects of superoxides, peroxides, hydroxyl radicals and singlet oxygen molecules. These include the preventative antioxidants catalase and peroxidase which decompose peroxide without generating free radicals, and chain-breaking antioxidants which scavenge radicals to stop free radical and chain propagation reactions. The water-soluble, aqueous phase, chain-breaking antioxidants include Vitamin C, uric acid, cysteine and glutathione, while the lipid soluble antioxidants such as Vitamin E function within membranes. A list of toxic oxidants and some of their known respective scavengers is presented in Table 3 below. It is highly likely that many more such natural scavengers exist in nature, awaiting our discovery.
Table 3. SOME ANTIOXIDANTS FOR REACTIVE OXYGEN SPECIES
OXIDANT SCAVENGER DIETARY ANTIOXIDANTS
Superoxide Superoxide Dismutase(SOD) Vitamin C, Rutin, Cysteine
Hydrogen Peroxide Catalase, Glutathione Vitamin C, Vitamin E,
Uric Acid Selenium
Hydroxyl Radical Cholesterol, Benzoate, Vitamin C, Rosemary, Sage
Dimethyl Sulfoxide (DMSO) Amygdalin, Anthocyanins
Formate, Uric Acid Cysteine
Singlet Oxygen Cholesterol, Bilirubin Vitamin E, BHT, Cholesterol
Histidine, Uric Acid Lemon Oil, Beta-Carotene
(from "Oxidology" Bradford, Allen & Culbert. 1985. Bradford Foundation(53))
Vitamin C scavenges superoxide and hydroxyl radical(182), as well as reacting directly with hydrogen peroxide, therefore protecting against various toxic free radicals which promote lipid peroxidation(33). For example, the generation of toxic oxygen species by phagocytes is associated with a number of chronic degenerative and inflammatory conditions, including cancer, arthritis and lung disease. Laboratory experiments have demonstrated that Vitamin C neutralizes these harmful oxidants derived from phagocytes(7). Vitamin C after being converted to dehydroascorbic acid by free radical reactions, is regenerated via the glutathione enzyme complex(161). It is interesting that the Vitamin C (ascorbate) free radical itself, rather than initiating radical chain reactions, does not react with oxygen and quenches itself very rapidly. And since Vitamin C reacts directly with hydrogen peroxide, it acts as a protectant against damage from lipid peroxides.
However, an even more fascinating chapter in the Vitamin C – free radical protection story is the finding that Vitamin C and Vitamin E work together, synergistically, in inhibiting the free radical chain oxidation of lipids(161). Vitamin C actually regenerates the Vitamin E radical, enabling these two potent anti-oxidants to cooperate in what is called "redox coupling". Vitamin E does its work within the membrane, while Vitamin C participates from the aqueous cellular compartment.
It had been noted previously that Vitamin C "spared" the consumption of Vitamin E in free radical chain oxidation experiments; however, it had never been shown whether Vitamin C, located in the aqueous part of the cell and Vitamin E, situated within the lipid membrane, could actually cooperate to prevent these detrimental lipid peroxidation events. Results reported on at the latest Vitamin C Conference showed that, in fact, even though Vitamin C is sequestered in the aqueous part of the cell and cannot penetrate the lipid membrane, that Vitamin C is accessible to the Vitamin E radical and does regenerate Vitamin E(161).
Multiple sources of free radicals abound – chemicals in our food, heating unsaturated oils, margarines and other unsaturated fats(74-5), not to speak of the toxic chemicals ingested from pesticides, nitrites, etc. etc. In the face of this growing menace from so many seeminagly unavoidable threats to our health, there would appear to be two typical "knee-jerk" reactions for the individual: 1) To scrupulously avoid contact with every conceivable toxic substance, environment, food and stress, since stress plays a major role in releasing free radicals; or 2) To throw up one's hands in despair and do nothing, deciding that it's just not possible to eliminate toxins from life in the twentieth century. The first response, taken to extremes, could lead to an acutely neurotic and/or hermetic lifestyle (taking to the clean air of the Himalayas to meditate alone for the rest of one's life); the second, likewise could provide an excuse or rationalization for laziness in controlling one's daily living habits.
What then, is a sensible response to this ever-mounting barrage to our health from so many sources? Is there something we can do in the face of so many health threats around every corner? It would certainly appear to make eminent sense to inform ourselves thoroughly and accurately about health risk factors such as free radicals and toxic oxygen species without going overboard in panic (we have survived this long, after all), and to implement as many health promoting measures in our lives as feels appropriate and convenient. Obviously there are degrees of urgency, depending upon our current state of health; someone seriously ill from cancer or arthritis is much more vulnerable to toxic overload than, say an Olympic decathalon athlete. Interestingly, however, it could be said that the average Olympic athlete is much more aware and careful about his/her health and environment than the rest of the population. And that could be the most eloquent testimony of all to taking responsibility for every aspect of our lifestyle.
The generous provision of natural anti-oxidants including Vitamin C in one's daily dietary regime would appear to make more than adequate sense in promoting better defense against those all-pervasive destructive free radical elements emanating from within and without our bodies.