Summary
Little is known about selenium intake and status
of athletes or changes in selenium status with
training. A few studies suggested a benefit of
selenium supplementation in improving antioxi-
dant capacity, but these studies require corrobo-
ration. It is possible that selenium may be most
effective in athletes who are ingesting insuffi-
cient amounts, yet it is not known if marginally
insufficient intake will compromise status or
antioxidant capacity. Excessive amounts of sele-
nium (> 200 mg · day–1) could have toxic effects
(Levander & Burk 1996; Boylan & Spallholz
1997).
Chromium
Chromium’s primary function is to potentiate
the effects of insulin in stimulating the uptake of
glucose, amino acids and triglycerides by cells
(Hunt & Groff 1990; Stoecker 1996; Anding et al.
1997). How chromium affects insulin action is
not fully known but chromium is thought to help
bind insulin to its receptor (Trent & Thieding-
Cancel 1995). Release of insulin may stimulate
the release of chromium from body stores
(Hunt & Groff 1990). The physiological role of
chromium was first identified when it was
shown that a substance containing chromium
was necessary for maintaining normal glucose
tolerance (Stoecker 1996; Anding et al. 1997). This
organic compound, referred to as the glucose
tolerance factor, was found to be a complex of
chromium, nicotinic acid and glutathione (Hunt
& Groff 1990).
In addition to insulin’s role in transport of
nutrients into muscle cells, it may act as a phys-
iological antagonist to bone resorption and
promote collagen production by osetoblasts
(McCarty 1995). At present there have been no
trials to assess chromium’s effectiveness on
bone health, but this may prove a fruitful area
for research, especially in amenorrhoeic athletes.
McCarty (1995) suggests that rather than relying
on mononutrient therapy with calcium, a
346 nutrition and exercise
micronutrient cocktail of several nutrients
that affect bone, such as calcium, chromium,
zinc, boron, copper and manganese and vitamins
D and K, be studied in the maintenance of bone
mineral density.
The US Food and Nutrition Board was unable
to establish an RDA for chromium due to insuffi-
cient data. Instead, the ESADDI is set at 50–
200 mg · day–1(Food and Nutrition Board 1989).
Many people may not be ingesting the minimum
ESADDI (Anderson et al. 1991; Stoecker 1996). A
diet that would appear adequate for most nutri-
ents can have less than 16mg of chromium per
4.2 kJ (1000 cal), and high-fat diets may have less
chromium than isocaloric low-fat diets (Stoecker
1996). Anderson and Kozlovsky (1985) analysed
the chromium content of 7-day self-selected diets
for 10 men and 22 women and found that the
mean (and range) chromium content of the food
was 33mg · day–1(range, 22–48) for the men and
25 mg · day–1(range, 13–36) for the women. Even
individuals with the largest content of chromium
in the diet had less than the minimum ESADDI.
However, there is some concern that the ESADDI
may be set too high because earlier studies used
less sophisticated equipment so that the require-
ment determination may have been inaccurately
high (Stoecker 1996).
Chromium ingestion has been related to
several health benefits. Studies have found that
subjects with impaired glucose tolerance who
were supplemented with chromium demon-
strated improved glucose tolerance (Anderson
1992). Chronic insufficient chromium ingestion
could predispose an individual to developing
glucose intolerance and maturity-onset diab-
etes (Anderson 1992). Chromium supplements
resulted in a lowering of blood lipids in subjects
with high values (Hermann et al. 1994), and one
study found that blood lipids were lowered in
bodybuilders taking chromium supplements
(Lefaviet al. 1993).
Food sources rich in chromium are Brewer’s
yeast, mushrooms, prunes, nuts, asparagus,
wine, beer and whole grains (Hunt & Groff
1990). Absorption of chromium is enhanced