Free
Radicals: How Vitamins Can Help
Free Radicals: How Vitamins Can Help
By: Dr. George Obikoya
A free radical is a chemical "species"
that contains an unpaired electron. This is very bad to have in
your body, because it wants to achieve stability. The only way to
do that is to combine, or "react" with other molecules.
Unfortunately, usually those molecules are important things like
DNA or our cells. A few stable free radicals are known but most
are very reactive (they want to combine with other molecules). In
free radical chain reactions, the radical product of one reaction
becomes the starting material for another, propagating free radical
damage - think out of control nuclear fission.
There are three steps to free-radical chain reaction: initiation,
propagation, and termination. In the initiation step, free radicals
are formed from molecules that readily give up electrons, such as
hydrogen peroxide. In the propagation steps, the chain-carrying
radicals are alternately consumed and produced. In the termination
steps, radicals are destroyed. Thus, without termination by an agent
such as an antioxidant, a single free radical can damage numerous
molecules, including your DNA.
There are four common oxygen metabolites in our
bodies that are free radicals: superoxide anion (O2- ), hydrogen
peroxide (H2O2), hydroxyl radical (OH ), and singlet oxygen (1O2).
These free radicals can be generated via a number of mechanisms,
including normal physiologic processes and processes resulting from
other external factors such as damage to the body or increased exercise.
For example, singlet oxygen is generated by photosensitization reactions
wherein a molecule absorbs light of a given wavelength, exciting
the molecule. This excited molecule transfers the increased energy
to molecular oxygen, creating singlet oxygen, which then can attack
other cell components and start a chain reaction.
It appears that the primary function of carotenoids, an important
class of antioxidants, is to scavenge free radicals, particularly
singlet oxygen produced by photosensitization.
A certain amount of oxidative function is necessary for proper health.
For example, oxidation processes are used by the body's immune systems
to kill microorganisms. Sometimes, however, the level of toxic reactive
oxygen intermediates (ROI) overcomes the antioxidant defenses of
the host, resulting in an excess of free radicals and a state called
oxidative stress. This process can be extremely damaging, as its
effects compound over time.
Free radicals can induce local injury by reacting with lipids, proteins,
and nucleic acids (such as DNA). The interaction of free radicals
with cellular lipids leads to membrane damage and the generation
of lipid peroxide byproducts. Interaction with nucleic acids leads
to a breakdown of our DNA and increased cellular death.
Cells contain a number of antioxidants that have various roles in
protecting against free radical reactions. The major water-soluble
antioxidant metabolites are glutathione (GSH), the B vitamins and
vitamin C. Many water-soluble enzymes also catalyze these reactions.
Vitamin E and the carotenoids are the principal lipid-soluble antioxidants.
Vitamin E is the major lipid-soluble antioxidant in cell membranes
that can break the chain of lipid peroxidation. Therefore, it is
the most important antioxidant in preventing oxidation of these
fatty acids. Vitamin E is recycled by a reaction with vitamin C,
so it is commonly suggested to take both vitamins E and C together.
Despite the actions of antioxidant nutrients, some oxidative damage
will occur, and accumulation of this damage throughout life is believed
to be a major contributing factor to aging and disease. Fortunately,
you can reduce the oxidative stress on your cells with common, inexpensive
vitamin supplements.
The Institute of Medicine (IOM) recently updated nutritional requirements
for the antioxidant nutrients (vitamin C, vitamin E, carotenoids,
and selenium), as well as other nutrients. In the past, Recommended
Dietary Allowances (RDAs) were used in the United States and Recommended
Nutrient Intakes (RNIs) were used in Canada. Since the last review
of these guidelines in 1989 and 1990, respectively, harmonized new
data have emerged reflecting dietary requirements of food components
and their role in maintaining health.
Reactive oxygen species are some of the most dangerous by-product
of our breathing. Fortunately, antioxidants help clear our body
of reactive oxygen intermediates (ROI). Nutritional antioxidants
are believed to have potential treatment for a wide variety of diseases,
including cancer, atherosclerosis, chronic inflammatory diseases,
even aging. Take vitamins E and C for example. Recent research shows
that in combination, these vitamins in combination were extremely
effective at lowering your risk of developing Alzheimer's disease.
An antioxidant is a substance that in low concentrations relative
to the oxidizable substrate substantially delays or reduces oxidation
of the substrate . Antioxidants fight oxidation, hence their name.
They protect other chemicals in our body from toxic oxidation reactions
by reacting with free radicals and other reactive oxygen species,
essentially derailing the oxidation process. In a way similar to
how sunblock works, the antioxidant (such as Vitamin E) sacrifices
itself by being oxidized during this reaction.
Because your antioxidant supply is limited, as one antioxidant molecule
is only capable of reacting with one free radical, you need to regularly
replenish your antioxidant supplies via vitamin supplementation.
There are many antioxidants including vitamin C, vitamin E, selenium,
and the carotenoids and a multitude of other nutrients, including
minerals such as copper, manganese, and zinc, flavonoids (such as
grape seed extract and phenols found in green tea) and coenzyme
Q10 that are all powerful antioxidants.
Because vitamin C is water soluble, its antioxidant functions take
place in aqueous body compartments. It also helps protect low-density
lipoprotein cholesterol (LDL-C) against free radical damage. As
an antioxidant, it helps protect against cancer, cardiovascular
disease, and certain effects of aging. Vitamin E is fat soluble,
so its antioxidant properties are best used by fattier parts of
the body such as the brain.
Unlike other vitamins, which are involved in metabolic reactions,
it appears that the primary role of vitamin E is to act as an antioxidant.
Vitamin E is incorporated into the lipid portion of cell membranes
and other molecules, protecting these structures from oxidative
damage and preventing the propagation of lipid peroxidation. Vitamin
E can protect us against cancer, heart disease, and complications
of diabetes.
The only specific known purpose of carotenoids in humans is to act
as a source of vitamin A in the diet, but they also have important
antioxidant effects. The latter are based on the caretenoids' ability
to quench singlet oxygen and trap peroxyl radicals, thereby preventing
lipid peroxidation. As a result, carotenoids protect against the
development of cancer, cardiovascular disease, and ocular (eye)
disorders.
Carotenoids also affect cell growth regulation and gene expression.
Diets low in carotenoids may lead to increased risk of cancer and
heart disease. Lycopene is the most potent antioxidant for quenching
single oxygen and scavenging free radicals.
A good multivitamin is the foundation of health
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References
Corrigan JJ Jr, Marcis FI. Coagulopathy associated with vitamin
E ingestion. JAMA. 1974;230:1300-1.
Kim JM, White RH. Effect of vitamin E on the anticoagulant response
to warfarin. Am J Card. 1996;77:545-6.
Paiva SAR, Russel RM. Beta-carotene and other carotenoids as antioxidants.
J Am Coll Nutr. 1999;18:426-33.
Gerster H. The potential role of lycopene for human health. J Am
Coll Nutr. 1997;16:109-26.
Goodman DS Goodman DS. Vitamin A and retinoids in health and disease.
N Engl J Med. 1984;310:1023-31.
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