kidney and skeletal muscle of male Wistar rats.
Lipoate supplementation significantly increased
total GSH levels in liver and blood. These results
are consistent with those from previously dis-
cussed cell experiments, and show that indeed
lipoate supplementation may increase GSH
levels of certain tissues in vivo. Lipoate supple-
mentation, however, did not affect the total GSH
content of organs such as the kidney, heart and
skeletal muscles. Lipoate supplementation-
dependent increase in hepatic GSH pool was
associated with increased resistance to lipid per-
oxidation. This beneficial effect against oxidative
lipid damage was also observed in the heart and
red gastrocnemius skeletal muscle. Lower lipid
peroxide levels in certain tissues of lipoate fed
rats suggest strengthening of the antioxidant
network defence in these tissues (Khanna et al.
1997).
From the biochemistry of antioxidant action it
is evident that antioxidants function in a network
and interaction between several major antioxi-
dants have been clearly evident. As a result,
some studies have attempted to investigate the
efficacy of a combination of several antioxidants
as supplements (Viguie et al. 1989; Kanter &
Eddy 1992; Kanter et al. 1993). Supplementation
of individuals with a vitamin mixture containing
37.5 mg b-carotene, 1250 mg vitamin C and 1000
IU of vitamin E for 5 weeks decreased the level of
lipid peroxidation by-products in the serum and
breath, both at rest and following exercise at both
60% and 90% V
.
o2max.(Kanteret al. 1993). In con-
trast, a previous study, which used a similar
mixture of antioxidants and exercised the sub-
jects at 65% of maximal heart rate in a downhill
run, was unable to demonstrate any positive
effects (Kanter & Eddy 1992). This inconsistency
in observation was explained by differences in
the nature and intensity of the exercise in the two
studies. The effects of an antioxidant mixture
(10 mg b-carotene, 1000 mg vitamin C and 800 IU
of vitamin E) on human blood GSH system and
muscle damage has been determined (Viguie et
al.1989). A protective effect on the blood GSH
system and muscle damage was evident. A ran-
domized and placebo-controlled study has been
310 nutrition and exercise
carried out on 24 trained long-distance runners
who were substituted with a-tocopherol (400 IU ·
day–1) and ascorbic acid (200 mg daily) for 4.5
weeks before a marathon race. Serum content of
ascorbic acid as well as a-tocopherol were ele-
vated in supplemented individuals. In this study
the antioxidant supplementation protocol was
observed to significantly protect against
exercise-induced muscle damage as manifested
by the loss of creatine kinase from the muscle to
the serum (Rokitzki et al. 1994b).Perspectives
Several lines of evidence consistently show that
physical exercise may induce oxidative stress.
The relationship between physical activity,
physical fitness and total radical trapping antiox-
idant potential was examined in the Northern
Ireland Health and Activity Survey. This was a
large cross-sectional population study (n=1600)
using a two-stage probability sample of the pop-
ulation. A necessity for antioxidant supplemen-
tation, especially in physically active and fit
individuals, was indicated (Sharpe et al. 1996).
Depending on nutritional habits and genetic dis-
position, susceptibility to oxidative stress may
vary from person to person. Determination of
tissue antioxidant status of individuals is thus
recommended. Such information will be neces-
sary to identify specific necessities and formulate
effective antioxidant therapy strategies. Nutri-
tional antioxidant supplements are known to
be bioavailable to tissues and may strengthen
defence systems against the ravages of reactive
oxygen. Results from antioxidant supplementa-
tion studies considerably vary depending on the
study design and measures of outcome. Physical
performance is regulated by multifactorial
processes and may not serve as a good indicator
to test the effect of antioxidant supplementation.
The general trend of results show no effect of
antioxidant supplementation on physical perfor-
mance. However, in a large number of studies it
has been consistently evident that antioxidant
supplementation protects against exercise-
induced tissue damage. The diet of laboratory