"Look and feel younger!" "Reverse the aging process!" "Boost your
energy!" What could possibly do all that? -- antioxidants, devoted
pill-poppers will tell you, despite the fact that the Food and Drug
Administration (FDA) has prohibited manufacturers from claiming that
consuming their antioxidant products will reduce disease risk.
Each year, countless hopeful Americans shell out billions of dollars on
antioxidant supplements (nearly $2 billion, in fact, just on beta
carotene and vitamins C and E), believing they will dramatically lower
their risk of cancer, heart disease, and memory loss. Most experts
agree, however, that taking antioxidants is not a shortcut to good
health or the answer to staying young. So, where does that leave us?
In
this article, you'll learn the truth about antioxidants: what they are,
how they function, how much of them you need, where to find the best
dietary sources, and what the latest scientific research shows.
Vitamin
E is actually a generic term that refers to all entities (eight found
so far) that exhibit biological activity of the isomer tocopherol (an
isomer is one of two or more molecules that have the same chemical
formula but different atomic arrangements). Alpha-tocopherol, the most
widely available isomer, has the highest biopotency, or strongest
effect in the body. Because it is fat-soluble (and can only dissolve in
fats), alpha-tocopherol is in a unique position to safeguard cell
membranes -- largely composed of fatty acids -- from damage by free
radicals. Alpha-tocopherol also protects the fats in low-density
lipoproteins (LDLs, or the "bad" cholesterol) from oxidation.
Vitamin
C, also known as ascorbic acid, is a water-soluble vitamin. As such, it
scavenges free radicals that are in an aqueous (watery) environment,
such as inside your cells. Vitamin C works synergistically with vitamin
E to quench free radicals. Vitamin C also regenerates the reduced
(stable) form of vitamin E.
Beta-carotene, also a water-soluble
vitamin, is the most widely studied of the 600 carotenoids identified
to date. It is thought to be the best quencher of singlet oxygen (an
energized but uncharged form of oxygen that is toxic to cells).
Beta-carotene is also especially excellent at scavenging free radicals
in low oxygen concentration.
Selenium is a trace element. It is
a mineral that we need to consume in only very small quantities, but
without which we could not survive. It forms the active site of several
antioxidant enzymes including glutathione peroxidase.
Similar to
selenium, the minerals manganese and zinc are trace elements that form
an essential part of various antioxidant enzymes.
Antioxidant Enzymes
The antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and
glutathione peroxidase (GPx) serve as your primary line of defense in
destroying free radicals.
SOD first reduces (adds an electron to) the radical superoxide (O2-) to form hydrogen peroxide (H2O2) and oxygen (O2).
2O2- + 2H --SOD--> H2O2 + O2
Catalase
and GPx then work simultaneously with the protein glutathione to reduce
hydrogen peroxide and ultimately produce water (H2O).
2H2O2 --CAT--> H2O + O2
H2O2 + 2glutathione --GPx--> oxidized glutathione + 2H2O
(The oxidized glutathione is then reduced by another antioxidant enzyme -- glutathione reductase.)
Together,
they repair oxidized DNA, degrade oxidized protein, and destroy
oxidized lipids (fat-like substances that are a constituent of cell
membranes). Various other enzymes act as a secondary antioxidant
defense mechanism to protect you from further damage.
Other Antioxidants
In addition to enzymes, vitamins, and minerals, there appear to be many
other nutrients and compounds that have antioxidant properties. Among
them is coenzyme Q10 (CoQ10, or ubiquinone), which is essential to
energy production and can also protect the body from destructive free
radicals. Also, uric acid, a product of DNA metabolism, has become
increasingly recognized as an important antioxidant. Additionally,
substances in plants called phytochemicals are being investigated for
their antioxidant activity and health-promoting potential.
Do Antioxidants Improve Health?
Since antioxidants counteract the harmful effects of free radicals, you
would think that we should consume as much as of them as possible. The
truth is, although there is little doubt that antioxidants are a
necessary component for good health, it is not clear if supplements
should be taken and, if so, how much. Once thought to be harmless, we
now know that consuming mega-doses of antioxidants can be harmful due
to their potential toxicity and interactions with medications. Remember
-- antioxidants themselves may act as pro-oxidants at high levels.
So, is there any basis for the hoopla? The experimental (intervention) studies completed so far have had mixed results:
*
The Alpha-Tocopherol Beta-Carotene Cancer Prevention Study (ATBC)
involved Finnish men who were heavy smokers and alcohol drinkers. The
volunteers were either given 20 milligrams (mg) of synthetic
beta-carotene, 50 mg of vitamin E, a combination of the two, or a
placebo. After eight years, the men who took vitamin E had 32 percent
fewer diagnoses of prostate cancer and 41 percent fewer prostate cancer
deaths compared to men who did not. However, after only four years,
there were 16 percent more cases of lung cancer and 14 percent more
lung cancer deaths in the beta-carotene-only group.
* In the
Carotenoid and Retinol Efficacy Trial (CARET), volunteers were either
smokers or asbestos workers. They were given a combination of 30 mg of
synthetic beta-carotene and 25,000 International Units (IU) of retinol
(pre-formed vitamin A) or placebo. This study was stopped early due to
the fact that preliminary findings suggested that there was a
28-percent increase in lung cancer rates in the beta-carotene group
compared to the placebo group.
* The Physicians' Health Study
(PHS) of 22,000 physicians, 11 percent of whom were smokers and 40
percent were past smokers, showed neither a protective effect nor a
toxic effect after 12 years of follow-up. The participants were
randomized to receive either 50 mg of beta-carotene every other day or
placebo. (A second PHS underway is testing beta-carotene, vitamin E,
vitamin C, and a multivitamin with folate in healthy men age 65 and
older for slowing cognitive decline.)
* A 1997 study published
in the Journal of the American Medical Association found that 60 mg of
vitamin E a day strengthened the immune system in a group of healthy
patients at least 65 years old, and 200 mg generated a four-to-six fold
improvement after four months. However, 800 mg of vitamin E resulted in
worse immunity than receiving no vitamin E at all.
* In 2001,
the Age-Related Eye Disease Study (AREDS), a randomized,
placebo-controlled clinical trial, showed that high-dose
supplementation of 500 mg of vitamin C, 400 IU of vitamin E, 15 mg of
beta-carotene, 80 mg of zinc, and 2 mg of copper significantly reduced
development of advanced age-related macular degeneration (AMD) compared
to placebo. In addition, the antioxidant-plus-zinc group had
significant reduction in rates of at least moderate visual acuity loss.
There are several possible explanations to account for the results.
* The amount of antioxidants in supplements may be so high compared with that in the diet that it leads to a toxic effect.
* Other nutrients may be present in fruits and vegetables that work in
sync with antioxidants and are necessary to provide a protective effect.
* The study participants may have been too old to start taking
antioxidants, or they may have led lifestyles that were too unhealthy
for the antioxidants to make a positive difference.
Furthermore,
literally hundreds, if not thousands, of observational studies (where
investigators look for associations without giving participants
supplements to take) have linked diets rich in antioxidant-rich fruits
and vegetables to a lower risk for diseases like cancer, heart disease,
stroke, cataracts, Parkinson's, Alzheimer's, and arthritis. So, despite
the disappointing findings of trials, scientists remain certain of the
many potential benefits of dietary antioxidants -- they simply haven't
figured out exactly how the different antioxidant systems work together
in our bodies to protect us from free-radical damage.
How Much Do I Need?
The American Heart Association, for one, does not recommend using
antioxidant supplements "until more complete data are in," but instead,
suggests "people eat a variety of foods daily from all of the basic
food groups." Moreover, in April 2000, the Food and Nutrition Board of
the Institute of Medicine, an advisory group that is part of the
National Academy of Sciences, reported that Vitamin C, vitamin E,
selenium, and carotenoids like beta-carotene should come from food, not
supplements. After examining available data on the beneficial and
harmful health effects of antioxidants, the panel concluded that there
isn't enough evidence to support using large doses of these nutrients
to combat chronic diseases. In fact, the group warned that extremely
high doses of antioxidants may lead to health problems, including
diarrhea, bleeding, and the risk of toxic reactions.
Since 1941,
the Food and Nutrition Board has determined the types and quantities of
nutrients that are needed for healthy diets by reviewing scientific
literature, considering how nutrients protect against disease, and
interpreting data on consumption of nutrients. For each type of
nutrient, the Board has established a Recommended Dietary Allowance
(RDA)-a daily intake goal for nearly all (98 percent) healthy
individuals, and a "tolerable upper intake level" (UL)-the maximum
amount of a nutrient that healthy individuals can take each day without
risking adverse health effects. In some cases, the Board has decided
there isn't enough evidence to determine the amount at which a
particular nutrient is essential or harmful to health.
Where Antioxidants Are Found
Although research may look promising, particularly with regard to
vitamin E, food remains the smart choice for where to obtain your
antioxidants. Studies consistently demonstrate that for optimum health,
you should eat at least five servings of fruits and vegetables everyday
as part of a balanced diet. Below is a list of where to find specific
antioxidants. If you are interested in taking antioxidant supplements,
talk to your doctor about what is right for you.
This article taken from
http://health.howstuffworks.com/life-stages/aging/antioxidant6.htm
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