Selenium intake and plasma levels were exam-
ined before and after a week of sustained physi-
cal activity, psychological stress and lack of sleep
in Navy Seals during ‘Hell Week’ (Singh et al.
1991). Physical activity stress included simulated
combat exercise and obstacle course trials;
psychological stress included performance
anxiety, verbal confrontation and uncertainty of
events. Selenium intake was substantially higher
during Hell Week, but plasma selenium values
at the end of the week were lower. Lower
serum selenium values may reflect a redistri-
bution of selenium to other tissues requiring
antioxidant protection (Singh et al. 1991). The
authors suggested that the decrease in selenium
and other accompanying changes, such as a
decrease in plasma zinc, iron and albumin, and
an increase in ferritin, ceruloplasmin, white
blood cell count and creatine kinase, were indica-
tive of an acute-phase response to tissue damage
and the inflammatory effect of prolonged physi-
cal activity.
Fogelholm et al. (1991) examined serum
micronutrient levels in a sailing crew during a
transatlantic race and compared these values to
those of a control group. While there was no pre-
to postrace difference in serum selenium values,
the values for the sailors were lower than the
control values. Whether this indicates a slight
lowering of serum selenium values with training
is not known. It should be noted that the values
for the sailors were within the reference range.
However, if exercise results in an increase in
oxidative stress, the body may require greater
than reference levels of selenium (and other
antioxidants) to keep pace (Duthie 1996). This
does not necessarily mean that more selenium
should be ingested, because the body may
become more efficient in retention or action in
trained individuals.
Selenium supplementation and
lipid peroxidation
Two of the first studies to examine the effects of
selenium supplementation used a crossover
design, where the length of time of the washout
may not have been adequate. Draˇgan et al.(1990)
examined the effect of an acute dose of 140mg of
selenium or placebo in trained Romanian swim-
mers, where subjects repeated the treatment after
1 week. In a second experiment, 100mg of sele-
nium (or placebo) were administered for 14 days
and then the treatments were crossed for another
14 days with no washout period in between.
Before and after the treatments, subjects per-
formed a 2-h endurance swimming exercise. The
acute dose resulted in no significant change in
the exercise-induced increase in lipid peroxides.
However, after 14 days of supplementation, the
group who received the selenium supplement on
the second bout showed a decrease in lipid per-
oxides in response to the exercise. This was not
true for the group who received the selenium
first.
A second study by the same laboratory
(Draˇ gan et al.1991) found that 3 weeks of supple-
menting with a mixture containing selenium,
vitamin E, glutathione and cysteine (concentra-
tions were unspecified) in trained Romanian
cyclists resulted in a smaller change in lipid per-
oxidation compared with the group ingesting a
placebo. After 1 week, the groups crossed over,
but the group taking the placebo showed less of
an increase in lipid peroxides. It appeared the
first leg of the crossover may have affected the
response to the second leg of the crossover.
Tessier et al. (1995a, 1995b) administered
180 mg · day–1of selenium or a placebo for 10
weeks during an endurance training programme
after a 4-week deconditioning period. The sele-
nium supplement resulted in an increase in the
resting plasma levels of glutathione peroxidase
activity. A moderate correlation between erythro-
cyte glutathione peroxidase activity and V.
o2max.
was found in the supplemented group only
(Tessier et al. 1995a), but the supplement did not
affect V.
o2max.. In another report from the same
study (Tessier et al. 1995b), there was an increase
in muscle glutathione peroxidase activity in
response to an acute exercise bout in the supple-
mented group only (Tessier et al. 1995b). These
results lend support for selenium supplements
enhancing antioxidant capacity.