Antioxidants are intimately involved in the prevention of cellular damage
-- the common pathway for cancer, aging, and a variety of diseases. The
scientific community has begun to unveil some of the mysteries surrounding
this topic, and the media has begun whetting our thirst for knowledge.
Athletes have a keen interest because of health concerns and the prospect of
enhanced performance and/or recovery from exercise. The purpose of this
article is to serve as a beginners guide to what antioxidants are and to
briefly review their role in exercise and general health. What follows is
only the tip of the iceberg in this dynamic and interesting subject.
It's the radicals, man
Free radicals are atoms or groups of atoms with an odd (unpaired) number of electrons and can be formed when oxygen interacts with certain molecules. Once formed these highly reactive radicals can start a chain reaction, like dominoes. Their chief danger comes from the damage they can do when they react with important cellular components such as DNA, or the cell membrane. Cells may function poorly or die if this occurs. To prevent free radical damage the body has a defense system of antioxidants.
Antioxidants are molecules which can safely interact with free radicals
and terminate the chain reaction before vital molecules are damaged.
Although there are several enzyme systems within the body that scavenge free
radicals, the principle micronutrient (vitamin) antioxidants are vitamin E,
beta-carotene, and vitamin C. Additionally, selenium, a trace metal that is
required for proper function of one of the body's antioxidant enzyme
systems, is sometimes included in this category. The body cannot manufacture
these micronutrients so they must be supplied in the diet.
Vitamin E : d-alpha tocopherol. A fat soluble vitamin present in nuts,
seeds, vegetable and fish oils, whole grains (esp. wheat germ), fortified
cereals, and apricots. Current recommended daily allowance (RDA) is 15 IU
per day for men and 12 IU per day for women.
Vitamin C : Ascorbic acid is a water soluble vitamin present in citrus
fruits and juices, green peppers, cabbage, spinach, broccoli, kale,
cantaloupe, kiwi, and strawberries. The RDA is 60 mg per day. Intake above
2000 mg may be associated with adverse side effects in some individuals.
Beta-carotene is a precursor to vitamin A (retinol) and is present in liver,
egg yolk, milk, butter, spinach, carrots, squash, broccoli, yams, tomato,
cantaloupe, peaches, and grains. Because beta-carotene is converted to
vitamin A by the body there is no set requirement. Instead the RDA is
expressed as retinol equivalents (RE), to clarify the relationship. (NOTE:
Vitamin A has no antioxidant properties and can be quite toxic when taken in
excess.)
Preventing cancer and heart disease -- do antioxidants help?
Epidemiologic observations show lower cancer rates in people whose diets
are rich in fruits and vegetables. This has lead to the theory that these
diets contain substances, possibly antioxidants, which protect against the
development of cancer. There is currently intense scientific investigation
into this topic. Thus far, none of the large, well designed studies have
shown that dietary supplementation with extra antioxidants reduces the risk
of developing cancer. In fact one study demonstrated an increased risk of
lung cancer in male smokers who took antioxidants vs. male smoker who did
not supplement. Whether this effect was from the antioxidants is unknown but
it does raise the issue that antioxidants may be harmful under certain
conditions.
Antioxidants are also thought to have a role in slowing the aging process
and preventing heart disease and strokes, but the data is still
inconclusive. Therefore from a public health perspective it is premature to
make recommendations regarding antioxidant supplements and disease
prevention. New data from ongoing studies will be available in the next few
years and will shed more light on this constantly evolving area. Perhaps the
best advice, which comes from several authorities in cancer prevention, is
to eat 5 servings of fruit or vegetables per day.
Exercise and oxidative damage
Endurance exercise can increase oxygen utilization from 10 to 20 times
over the resting state. This greatly increases the generation of free
radicals, prompting concern about enhanced damage to muscles and other
tissues. The question that arises is, how effectively can athletes defend
against the increased free radicals resulting from exercise? Do athletes
need to take extra antioxidants?
Because it is not possible to directly measure free radicals in the body,
scientists have approached this question by measuring the by-products that
result from free radical reactions. If the generation of free radicals
exceeds the antioxidant defenses then one would expect to see more of these
by-products. These measurements have been performed in athletes under a
variety of conditions.
Several interesting concepts have emerged from these types of experimental
studies. Regular physical exercise enhances the antioxidant defense system
and protects against exercise induced free radical damage. This is an
important finding because it shows how smart the body is about adapting to
the demands of exercise. These changes occur slowly over time and appear to
parallel other adaptations to exercise.
On the other hand, intense exercise in untrained individuals overwhelms
defenses resulting in increased free radical damage. Thus, the "weekend
warrior" who is predominantly sedentary during the week but engages in
vigorous bouts of exercise during the weekend may be doing more harm than
good. To this end there are many factors which may determine whether
exercise induced free radical damage occurs, including degree of
conditioning of the athlete, intensity of exercise, and diet.
Can antioxidant supplements prevent exercise induced damage or enhance
recovery from exercise?
Although it is well known that vitamin deficiencies can create difficulties
in training and recovery, the role of antioxidant supplementation in a well
nourished athlete is controversial. The experimental studies are often
conflicting and conclusions are difficult to reach. Nevertheless, most of
the data suggest that increased intake of vitamin E is protective against
exercise induced oxidative damage. It is hypothesized that vitamin E is also
involved in the recovery process following exercise. Currently, the amount
of vitamin E needed to produce these effects is unknown. The diet may supply
enough vitamin E in most athletes, but some may require supplementation.
There is no firm data to support the use of increased amounts of the other
antioxidants.
Performance
In general, antioxidant supplements have not been shown to be useful as performance enhancers. The one exception to this is vitamin E which has been shown to be useful in athletes exercising at high altitudes. A placebo controlled study done on mountaineers demonstrated less free radical damage and decline in anaerobic threshold in those athletes supplemented with vitamin E. Although difficult to generalize, this finding suggests that supplementation with vitamin E might be beneficial in those triathletes who are adapting to higher elevations.
How much is enough?
Although there is little doubt that antioxidants are a necessary
component for good health, no one knows if supplements should be taken and,
if so, how much. Antioxidants supplements were once thought to be harmless
but increasingly we are becoming aware of interactions and potential
toxicity. It is interesting to note that, in the normal concentrations found
in the body, vitamin C and beta-carotene are antioxidants; but at higher
concentrations they are pro-oxidants and, thus, harmful. Also, very little
is known about the long term consequences of megadoses of antioxidants. The
body's finely tuned mechanisms are carefully balanced to withstand a variety
of insults. Taking chemicals without a complete understanding of all of
their effects may disrupt this balance.
Recommendations
1. Follow a balanced training program that emphasizes regular exercise and eat 5 servings of fruit or vegetables per day. This will ensure that you are developing your inherent antioxidant systems and that your diet is providing the necessary components.
2. Weekend warriors should strongly consider a more balanced approach to exercise. Failing that, consider supplementation.
3. For extremely demanding races (such as an ultradistance event), or when adapting to high altitude, consider taking a vitamin E supplement (100 to 200 IU, approximately 10 times the RDA) per day for several weeks up to and following the race.
4. Look for upcoming FDA recommendations, but be wary of advertising and media hype.
5. Do not oversupplement.
Source:
Antioxidants and Free radicals
http://www.rice.edu/~jenky/sports/antiox.html
