suggest that vanadyl sulphate will have any ben-
eficial effects for athletes.
Boron
Boron has been found to be an essential element
for plant growth, and it may be an essential nutri-
ent for animals (Food and Nutrition Board 1989;
Nielsen 1996). Boron affects calcium and magne-
sium metabolism and can influence membrane
function (Chrisley 1997). Nielsen et al. (1987)
found that boron supplementation of 3 mg · day–1
lowered urinary calcium loss in a low-
magnesium diet and increased serum oestrogen
and testosterone in postmenopausal women.
These data suggested that boron may play a role
in the prevention of bone loss (Volpe et al. 1993a,
1993b). Also, boron supplements have been pur-
ported to increase testosterone and muscle mass
in athletes (Green & Ferrando 1994).
There is a paucity of information on boron
requirements in general (there is no RDA or
ESADDI set) and no information on dietary
intake or status in athletes. A national database
for boron content of foods does not yet exist so it
is impossible to evaluate boron intake. However,
the average daily intake of boron is estimated to
range between 0.5 and 3.1 mg (Nielsen 1996).
Rich food sources of boron are leafy vegetables,
nuts, legumes and non-citrus fruits (Nielsen
1996).
A few studies of boron supplementation in
athletes exist. Meacham et al. (1994, 1995) and
Volpe et al. (1993a, 1993b) examined the effect of
3 mg · day–1of boron (or placebo) for 10 months in
four groups of subjects: athletes taking boron,
athletes taking placebo, sedentary taking boron,
and sedentary taking placebo. Serum phospho-
rus concentrations were lower and serum mag-
nesium higher in the subjects taking the boron
supplement. The sedentary subjects taking boron
had the lowest serum phosphorus levels and the
highest serum magnesium levels. Urinary boron
increased in the subjects supplemented with
boron. Bone mineral density was not affected by
boron supplementation, nor were circulating
levels of 1,25-dihydroxyvitamin D 3 , 17-boestra-
350 nutrition and exercise
diol, progesterone or testosterone. Thus, it
appeared that boron supplementation did not
affect bone mineral density or hormonal status,
but had some effect on mineral levels in the
blood. Whether these changes in serum phos-
phate and magnesium are meaningful remains to
be determined.
Green and Ferrando (1994) examined the effect
of 2.5 mg boron or placebo for 7 weeks in male
bodybuilders. Of the 10 subjects receiving the
boron supplement, six demonstrated an increase
in plasma boron levels. Both groups showed an
increase in lean body mass, total testosterone
level and strength over the course of the 7 weeks
but there was no difference between the group
taking the boron and the group taking the
placebo. At present there is not sufficient infor-
mation to suggest that boron supplements will
have any beneficial effects for athletes.Conclusion
Although athletes may not be ingesting sufficient
amounts of some trace minerals, in all cases,
an improved diet is recommended, or a multi-
vitamin–mineral supplement containing no
more than the RDA or ESADDI level. Despite a
lower dietary intake, often blood indicators of
status are normal, which may suggest that
dietary analyses are in error perhaps due to
under-reporting of certain foods or that data-
bases are inadequate. Futhermore, there may be a
long-term homeostatic adaptation to low
mineral intake. Exercise promotes a loss of some
trace minerals in sweat and urine, but it is not
known whether athletes can counteract this loss
by increasing absorption, retention, or efficiency
of the micronutrient. Thus, mineral balance
studies of athletes are needed. Also, exercise pro-
duces acute changes in trace minerals in the
blood but how this occurs has not been ade-
quately explained.
Supplementation of various micronutrients
on performance or body composition has not
proven very effective. There are no data to show
that zinc will enhance muscle growth or
testosterone levels. Unconfirmed results show