Journal of Sport Nutrition, 1992, 2, 111-122
©1992 Human Kinetics. This excerpt is approved by
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Efficacy of Chromium Supplementation in
Athletes: Emphasis on Anabolism
Robert G. Lefavi, Richard A.
Anderson, Robert E. Keith, G. Dennis Wilson, James L.
McMillan, and Michael H. Stone
Chromium in Physiological Systems
Soon after Curran
(17) suggested that chromium ions might have a biological
function, it was noted that glucose tolerance was impaired
in rats fed a chromium-poor diet (53). Subsequently, Schwarz
and Mertz (72) postulated the existence of an unrecognized
dietary factor that contains chromium and is necessary
for maintaining normal glucose tolerance in rats. This
dietary agent was termed glucose tolerance factor (GTF)
and trivalent chromium was later identified as its active
Since then, further research on this necessary role of
biologically active chromium has led to its general acceptance
as an essential trace element in humans. Although chromium's
essentiality has recently been challenged (36), a criticism
of this opinion clarified the manner in which chromium
functions as an essential nutrient (3). Furthermore, research
continues to identify chromium as the biologically active
component of a substance with GTF properties (87).
Glucose Tolerance Factor
function of GTF appears to be related to its organic structure.
Mertz (48) has specified markers of true GTF activity
and other researchers have attempted to identify the exact
structure of this compound. GTF has been hypothesized
(22) to be a low molecular weight compound, and nicotinic
acid, glycine, glutamic acid, and cysteine have been associated
as the GTF components associated with chromium (57,77).
Consistent with these findings, further research has suggested
that a nicotinic acid - chromium structure is essential
in the GTF complex (61,62,78), although the exact structure
of GTF (2) and the exact location of its synthesis is
Chromium Insulin Interaction
GTF has been shown to potentiate the effects
of insulin at target tissues (48,56,66), and other research
has documented a more direct chromium-insulin relation.
For instance, it appears that the presence of chromium
is required for the potentiation of insulin's actions
(49), perhaps explaining why chromium-deficient rats were
less responsive to insulin than chromium-supplemented
rats (45,65). Additionally, fasting serum chromium levels
were found to correlate with fasting serum insulin levels
(30,41), further suggesting that chromium and insulin
may be closely involved in a similar biological function.
A mechanism of action, whereby chromium acts as a ternary
complex with insulin and the insulin receptor to facilitate
a disulfide exchange at the target cell membrane, has
been proposed (15,32). Combined, these observations lead
to two conclusions. First, chromium may play a necessary
role in the normal physiological system by acting as a
"cofactor" for insulin, amplifying its actions
(46,67,75). Second, it logically follows that the efficiency
of insulin's effects - glucose, amino acid, and fatty
acid flux into the cell with subsequent glycogen, protein,
and triglyceride synthesis (16,29,76) - would be dependant
upon the maintenance of adequate chromium stores.
Investigators have found that biologically
active chromium concentrations vary in mammalian tissues.
Although it has been demonstrated that the liver contains
a substance with GTF properties (12,55), the kidneys,
spleen, and testes retain more chromium than other organs
(34). However, the concentration of chromium in chromium
stores may be altered by exercise since trained rats had
higher chromium levels in heart and kidney tissue compared
to controls (81). This apparent training adaptation may
occur due to the need for efficient pre-and post-exercise
insulin function, or it may result from a large amount
of glucose being processed during exercise. These studies
indicate that biologically active chromium may occupy
a special physiological pool that is mobilized when needed.
Given the possibility of a suboptimal chromium
status in regularly exercised individuals, it appears
that either a high-chromium diet or chromium supplementation
may be useful in athletes. Clearly, encouraging an athlete
to eat a high-chromium diet (unprocessed instead of processed
foods, a minimal consumption of sucrose-laden foods, etc.)
would also serve to establish good eating habits and should
be the first choice of any sport nutritionist.
However, there are few available foods that are also
good choices for athletes and exceptionally high in chromium.
Thus, athletes may need to eat much more food to ensure
adequate chromium intake, often a predicament for those
trying to restrict calories. In many cases the supplementation
of a chromium compound may be the most productive way
to protect endogenous chromium stores while avoiding the
addition of unwanted calories.
The restoration of depleted chromium stores would promote
optimal insulin function and may play a positive role
in exercise preparation, performance, and recovery. When
these issues are coupled with reports demonstrating the
biological activity (46,51,61,79,80) and very low toxicity
(51) of inorganic and GTF-like chromium compounds, the
concept of chromium supplementation in athletes mat be
more palatable to the most conservative sport nutritionist.
Supplements that are most likely to assist in restoring
chromium pools are inorganic chromium complexes such as
chromium chloride, and organic forms, both natural (Brewer's
yeast) and synthetic (GTF-like compounds).
Effects on Anabolism
One should be reasonable when counseling athletes
on chromium supplementation and the potential anabolic
nature of supplemental chromium. Even in an extreme case
whereby supplementation of biologically active chromium
restored depleted chromium pools, large, short-term muscle
mass increases would not be expected. Rather, marginal
body weight increases, occurring over a relatively long
period of time, would be more consistent with the anabolic
nature of enhanced insulin function..
That is, increasing insulin efficiency may improve anabolism
within muscle cells. However, a great deal of time, perhaps
many months, would be necessary for intracellular protein
synthesis to be sufficiently stimulated such that lean
body mass differences would differ significantly between
treatment and placebo groups, particularly when dealing
with normal, healthy athletes. Moreover, since insulin
assists in fat storage, decreases in percentage of body
fat may not be detectable for a longer period of time,
if at all, depending on caloric intake.
Furthermore, preliminary body mass data from our recent
chromium supplementation study using male athletes as
subjects (40) support the concept that possible anabolic
increases are likely to be moderate and insignificant
when the supplementation period is brief. In this investigation
we have found no significant increases in body composition
parameters in weight-lifters following 8 weeks of supplementation
with a chromium-nicotinic acid (GTF-like) compound. In
short, anabolic steroid-like muscle mass increases do
not appear to be consistent with effects normally seen
when chromium in any form is added to the diet of a healthy
subject, regardless of the training regimen employed.
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