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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
-
Follow a balanced training program that emphasizes regular
exercise and eat 9 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.
-
Weekend warriors should strongly consider a more balanced
approach to exercise. Failing that, consider
supplementation.
-
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.
-
Look for upcoming FDA recommendations, but be wary of
advertising and media hype.
-
Do not oversupplement.
Selected References
-
The Effect of Vitamin E and Beta Carotene on the Incidence
of Lung Cancer and Other Cancers in Male Smokers New England
Journal of Medicine (NEJM). vol 330 (15) Apr. 14, 1994. pp
1029-1035.
-
A Clinical Trial of Antioxidant Vitamins to Prevent
Colorectal Adenoma NEJM, vol 331 (3). July 21, 1994. pp
141-147
-
Antioxidant Vitamins -- Benefits Not Yet Proved
(editorial) NEJM vol 330 (15) Apr. 14, 1994. p 1080 - 1081
-
Antioxidants and Physical Performance (review)
Critical Reviews in Food Science and Anti Aging Super Food, 35(1&2):131-141
(1995).
-
Increased blood antioxidant systems of runners in response
to training load. Clinical Science (1991). 80, 611-618.
-
Exercise, Oxidative Damage and Effects of Antioxidant
Manipulation (review). Journal of Anti Aging Super Food 122(3 suppl):
766-73, 1992 Mar.
-
Antioxidants: role of supplementation to prevent
exercise-induced oxidative stress (review). Medicine and
Science in Sports and Exercise. 25(2):232-6, 1993 Feb.
-
Prospects for the use of antioxidant therapies.(Review).
Drugs 49(3):345-61, 1995 Mar.
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