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The following is reprinted from the Townsend Letter for Doctors, by
permission.  Those with questions, or interest on the subject may call
360-385-6021 for more information.  If those reading this newsgroup find
the information interesting, the editor, Dr. Collin, has agreed to let me
post a number of articles each month from his magazine.  Let me know what
you think, flame me if you don't like the stuff.

by Anna MacIntosh, Ph.D.

Longitudinal changes in zinc status in untrained men: Effects of two
different 12-week exercise training programs and zinc supplementation
J Am Diet Assoc. 93(10): 1165, 1993.
Summary: Eigh{*filter*} young men were recruited for an aerobic training program
which included exercising at an intensity just below the level leading to
{*filter*} lactate accumulation (lactate below 4mmol/1) for 35 minutes three
times a week. Six{*filter*} young men were recruited to participate in an
aerobic/anaerobic training program which included 2 minute high intensity
interval training ({*filter*} lactate levels about 4 mmol/l) as well as the
aerobic training program described above. Subjects in each training group
were given 20mg of zinc or a placebo. {*filter*} and urine samples were taken
before and 12 weeks after the training program. Plasma zinc, urinary zinc,
and alkaline phosphatase activity were measured.
   Both training groups had a significant increase in Vo2max, but neither
training group had an increase in urinary zinc. Plasma zinc levels
decreased at a 6 week measurement time point in the aerobic training
group, whereas with the aerobic/anaerobic training group, the midpoint
plasma zinc significantly increased from baseline. By the endpoint
measurement plasma zinc had returned to baseline in both training groups.
There was no change in any zinc measurement associated with zinc
Commentary: The results of this small study suggest that training
intensity may alter the transient response in plasma zinc. Transient
changes in plasma zinc are not especially informative in terms of how
exercise intensity might impact zinc nutriture since plasma zinc is not
considered a very sensitive indicator of body zinc. {*filter*} levels of zinc
can vary under different conditions, e.g. hypozincemia as part of a fever
response, and are therefore problematic in terms of how to interpret the
meaning of changes in {*filter*} zinc.
   These authors did not find an increased urinary zinc after the training
program and therefore they would not see the need for people regularly
exercising to take zinc supplements. I would concur with this conclusion,
although given the generally low zinc intake in the standard American diet
and the possibility of especially low zinc intake on a high carbohydrate,
low flesh cooking.net">food diet of many endurance athletes, it might be prudent to pay
attention to zinc nutriture in endurance athletes. It also needs to be
remembered that the urine is not the only route of zinc excretion.

Selenium and training effects on the glutathione system and aerobic performance
Med Sci Sports Exerc 27(3): 390, 1995.
Summary: Twenty-four young male subjects were aerobically trained three
times per week, at 65% of their Vo2max, for ten weeks. Half the group was
supplemented with 180g of selenomethionine and the other half was given a
placebo during the ten week training program. {*filter*} was taken under basal
and following an exhaustive exercise bout. Total glutathione, oxidized
glutathione, plasma glutathione peroxidase, and plasma selenium was
   Total glutathione was reduced and oxidized glutathione was increased
following an exhaustive exercise bout. The effects of the training program
were to increase the reduced to oxidized glutathione ratio and increase
the glutathione peroxidase activity. Higher plasma selenium, higher plasma
and erythrocyte glutathione peroxidase activity were found in the selenium
supplemented group.
Commentary:  A decrease in the reduced/oxidized glutathione ratio
following a single exercise bout is consistent with the idea that
submaximal, endurance exercise leads to an increased production of free
radicals. The longer term effects of training seemed to counteract this
transient reduction in the glutathione, free radical protection system.
The training adaptation appeared to improve the individual1s main free
radical protection system. Could it be that weekend warrior type
exercisers are at a higher risk of excessive free radical production and
damage if they simply intermittently stress their body and don1t actually
   The supplementation of selenium seemed to further improve the trained
person1s antioxidant status, but it did not have any effect on exercise
performance. These results suggest a synergistic antioxidant effect of
selenium supplementation and regular aerobic exercise. It seems obvious
that extra selenium is not necessarily required for regular exercisers,
but just like sedentary people they need to be sure of adequate selenium
intakes for proper functioning of the glutathione antioxidant system.

Zinc loss in sweat of athletes exercising in hot and neutral temperatures
Int J Sport Nutr 3 :261, 1993.
Summary: Nine trained males and nine trained females volunteered to
undergo two separate bicycle exercise bouts. One exercise bout was
conducted at room temperature and the other exercise bout was conducted at
35 degrees centigrade (95 degrees F). Sweat rates and zinc sweat were
measured under each temperature condition.
   Sweat zinc concentrations were higher in exercisers exercising in a
neutral environment, however sweat rates were greater in the hot
environment therefore total zinc loss was similar for exercising in the
two different ambient temperatures. Since males had greater sweat rates
they had a greater total zinc loss compared with females.
Commentary: Since zinc is an important cofactor for over 100 different
enzymes including those enzymes whose activity would need to go up to
support aerobic exercise (i.e. malate dehydrogenase and carbonic
anhydrase), proper zinc nutriture is important to understand for the
active individual. Several studies have reported hypozincemia in endurance
athletes, which could be explained by increased surface losses of zinc.
   Zinc supplementation is not necessarily indicated for a person
endurance training just for fitness maintenance, but may be indicated for
males routinely exercising for more than an hour in an individual exercise
bout. At least at this time male endurance athletes seem to be at a
greater risk of poor zinc nutriture. It may be especially prudent to check
zinc status (WBC zinc considered most sensitive) of male endurance
athletes with clinical signs of compromised immunity, i.e. frequent upper
respiratory tract infections. If zinc supplementation is recommended
remember a little bit (2mg) of copper is also necessary to supplement to
ensure that zinc does not drive down copper levels. Remember copper
deficiency is associated with increased risk of cardiovascular disease
among other problems.

Urinary selenium status of healthy people
Eur J Clin Chem Clin Biochem 33: 127, 1995.
Summary: Eighty healthy volunteers provided a 24-hour urine sample and a
record of dietary and exercise practices. Selenium and creatinine was
measured in the urine samples. Urine creatinine levels were also measured
because of previous work which suggested that urine selenium levels were
influenced by the person1s muscle mass.
   The results suggest that women excrete more selenium than men when body
weight is taken into account and selenium excretion is  expressed as
selenium g/g of creatinine. Individuals who ate fewer protein-rich foods
had a lower selenium status. Smoking did not seem to affect the person1s
selenium status. Less urinary selenium was measured for those that
reported greater physical activity.
Commentary: Although this paper is more about appropriate measurement
techniques for selenium status, the finding that urinary selenium seems to
be affected by regular exercise is interesting. It may be that because of
a greater selenium loss via sweating with regular exercisers there is less
in the urine. There is certainly no indication that regular exercisers
have different selenium requirements than nonexercisers. Although it may
be important for regular exercisers to ingest protein-rich foods to ensure
adequate intake of selenium and adequate protection from higher free
radical production which seems to occur with exercise.
   It is very clear that besides selenium being a cofactor for glutathione
peroxidase it is also necessary for normal thyroid hormone function.
Selenium is a cofactor for type I deiodinase. This enzyme is important in
converting thyroxine to triiodothyronine, the active form of the thyroid
hormones. Normal thyroid hormone function is obviously an important factor
to consider in the differential of fatigue. For either people doing too
much (overtraining) exercise or have a limited exercise capacity,
significant fatigue can be an issue.

Submaximal, aerobic exercise training exacerbates the cardiomyopathy of
postweanling Cu-depleted rats
Biol Trace Elem Res 38: 251, 1993.
Summary: These authors wanted to know the effects of an aerobic exercise
program on young, copper deficient rats. Copper deficiency in animal
models leads to significant myocardial structural and functional
pathologies. Twenty-eight rats were divided into four groups: a sedentary
and copper-adequate diet, a sedentary and copper-deficient diet, an
exercise and copper-adequate diet, an exercise and copper deficient diet
group. The exercise groups were trained for one hour daily on a treadmill
for 8 weeks.
   Copper deficient rats were unable to complete the last three training
runs. No anemia or overt cardiac hypertrophy was noted in the copper
deficient rats, but upon dissection of the hearts a left ventricular
hypertrophy was noted in the copper depleted rats. Copper deficient
trained rats also exhibited greater collagen hyperplasia and infiltration
of phagocytes compared to all other groups. {*filter*} pressure was
significantly lower in the trained compared to the untrained rats, but
copper status had no effect on {*filter*} pressure. Liver superoxide di{*filter*}ase
activity (SOD) was the lowest in the trained copper deficient rats
compared to the other groups. Soleus muscle cytochrome C oxidase activity
(an enzyme of the electron transport chain) was greatest in the trained,
copper adequate group and lowest in the copper deficient sedentary group.
Copper deficient trained rats also had more myocardial ultrastructural
changes when compared with copper deficient sedentary rats.
Commentary: Because of the small number of rats used and the inevitable
question of 3are effects in rats similar to effects in humans,2 the
conclusions from this study must be viewed with caution. This animal study
should at least serve to remind us of the importance of adequate copper
intakes for normal cardiac health. The results these authors report
suggest that an individual who is copper deficient and is also exercising
may actually be putting themselves at greater risk for myocardial damage.
It certainly would appear prudent that copper status be measured in any
patient who should begin an exercise program as part of a cardiac
rehabilitation program and currently ingests the standard American diet.
One of the best measures of body copper status is red {*filter*} cell SOD.

Trace mineral requirements for athletes
Int J Sports Nutr 4: 104, 1994.
Summary: This review article is trying to answer the question of whether
athletes require more zinc, selenium, copper, and chromium. It seems
possible that athletes would have greater requirements of these nutrients
because of increased excretion, low dietary intakes, and the high use of
metabolic pathways which require these micronutrients as cofactors during
exercise. The data taken together suggest that athletes may excrete
excessive zinc and that female endurance athletes tend to have low zinc
intakes. There is no good evidence that zinc supplements can enhance
   Results of a number of studies would suggest that plasma copper levels
are not different in athletes compared to sedentary people. {*filter*} copper
levels reported following an acute exercise bout have ranged from
increased to decreased. The alteration of {*filter*} copper with exercise is
still unclear, although there is some concern of low body levels of copper
due to high vitamin C and random zinc supplementation.
   Strenuous training may lead to a decrease in {*filter*} selenium. The
selenium may be redistributed into tissues to help prevent lipid
peroxidation which tends to occur with more strenuous exercise. There is
no information at this time that exercise leads to an excessive loss of
Commentary: In general, it appears that so little is known about how to
interpret the tests for micronutrient levels that any concrete
recommendations for athletes regarding these three minerals is premature.
The nutritional literature would suggest that {*filter*} levels of zinc,
copper, and selenium are not the most accurate way to assess nutriture of
these different nutrients. On the other hand these micronutrients are
often low in the American diet, making athletes as vulnerable as any other
American for deficiencies of these micronutrients.

Mon, 10 Aug 1998 03:00:00 GMT
 [ 1 post ] 

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