Because selenium serves as an antioxidant,
adequate levels may reduce oxidative stress
during exercise and aid in recovery, thereby
allowing athletes to train harder. For more infor-
mation on selenium, oxidative stress and exer-
cise, see Aruoma (1994), Clarkson (1995) and
Halliwell (1996).
Selenium intake and status in athletes
The content of selenium in foods, especially
plants, is highly variable because of the varia-
tion in the soil content of selenium. Blood
selenium values vary among countries; for
example, they are relatively high for adults in the
USA and Canada, but low for adults in Sweden
and New Zealand, where soil content of sele-
nium is low (Hunt & Groff 1990). Food sources
of selenium are seafoods, liver, organ meats,
muscle meats, cereals and grain (Levander &
Burk 1996).
The RDA for selenium is 70 and 55mg for males
and females, respectively, 19 years and older
(Food and Nutrition Board 1989). There is no
completely acceptable measure of selenium
status (Gibson 1990). Whole blood or erythrocyte
measures are somewhat more accurate than
plasma or serum values that fluctuate from day
to day (Gibson 1990). However, published means
of serum selenium in adults are fairly consistent
varying from 0.53 to 2.4mmol·l–1(Malvyet al.
1993). The activity of glutathione peroxidase has
been used to assess selenium status, but normal
values have not been well standardized (Gibson
1990).
Little data exist on selenium intake or status of
athletes. Wrestlers were found to have intakes
of selenium below 90% of the RDA in about half
of those competing while only one in eight of
non-competing wrestlers had lower intakes than
the RDA (Snook et al. 1995). Despite the lower
selenium intake, selenium status assessed by
plasma and erythrocyte glutathione peroxidase
activity indicated that all wrestlers had adequate
status (Snook et al. 1995). Robertson et al. (1991)
reported that sedentary subjects had lower blood
glutathione peroxidase activity and concentra-
344 nutrition and exercise
tion of selenium than trained runners. And, of
the trained runners, those who trained 80–147
km · week–1had higher levels than those who
trained only 16–43 km · week–1for at least 2 years.
Athletes in countries where the food content of
selenium is adequate generally have adequate
status (Fogelholm & Lahtinen 1991; Wang et al.
1995). Wang et al. (1995) found that Swedish ori-
enteers had lower serum selenium values than
Finnish orienteers. Since 1984, Finland has been
enriching fertilizer with selenium to increase the
selenium content of cereal crops, which is not the
case in Sweden.Changes due to exercise
Few studies have examined either exercise
changes in blood selenium or glutathione peroxi-
dase. Duthie et al. (1990) reported no significant
change in erythrocyte glutathione peroxidase,
catalase or SOD activity after a half marathon
and up to 120 h postrace in trained subjects. In
contrast, sedentary subjects who exercised on a
cycle ergometer at 70% of maximal heart rate for
1 h showed decreases in erythrocyte enzyme
activities of superoxide dismutase, catalase and
glutathione peroxidase at 5 min after exercise
and remained low for up to 48 h (Toskulkao &
Glinsukon 1996). This change was accompanied
by an increase in plasma malondialdehyde, an
indirect indicator of increased lipid peroxidation.
Thus, the large production of free radicals may
result in a decrease in activity of the enzymes.
In the Duthie et al. study (1990), trained subjects
may be better able to handle the increase in free
radicals such that changes in these enzyme
activities were not apparent.
Toskulkao and Glinsukon (1996) also exam-
ined the changes in antioxidant enzyme activity
in trained athletes but the results were inconsis-
tent. Rokitzki et al. (1994) found that trained ath-
letes did not show an increase in activity of
glutathione peroxidase in erythrocytes after a
marathon. However, these authors suggested
that the lack of change may be due to the inap-
propriate use of erythrocytes rather than muscle
where the greater stress is taking place.