by Michael Nickels, M.D., Ph.D.
Several people have asked me recently about the dietary
supplement creatine, its ability to boost athletic
performance and any dangers that may be associated with
its use.
When dealing with dietary supplements, it is always best
to remember the caveat “let the buyer beware.” According
to the Nutrition Business Journal, which provides
market research for the dietary supplement industry,
U.S. sales of pills, powders, bars, and beverages to
boost athletic performance reached $1.26 billion in
1997. This market was expected to grow by 6–10% in 1998.
The sale of creatine, in particular, rose from $30
million in 1995 to an expected $200 million in 1998.
Thus, the economic pressure to hype athletic benefits
from dietary supplementation is enormous, and marketing
claims typically range from exaggerations to outright
lies.
Furthermore, since the dietary supplement industry is
not regulated by the Food and Drug Administration, these
substances are not subject to the same scientific and
manufacturing scrutiny as medically prescribed drugs.
While many vitamins, herbs and dietary supplements may
be beneficial to our health and increase athletic
performance, we should always maintain a certain degree
of skepticism and not blindly buy into the industry
hype. Decisions to supplement your diet with these
substances should be based on an examination of the
scientific literature and your supply should be
purchased only from reputable sources.
This being said, what is the current evidence for and
against the use of creatine to improve athletic
performance?
Creatine is a peptide (small protein) made from the
amino acids glycine, arginine and methionine. The
average 70 kilogram male contains 120 grams of creatine,
95% of which is in skeletal muscle. Stores of creatine
are maintained from ingestion of fish and meat products,
as well as from production in the liver. Oral ingestion
of excess creatine has been shown to reversibly inhibit
its production in the liver and, once our skeletal
muscles become saturated with creatine, the excess is
filtered by the kidneys, then removed in the urine.
Conversely, an absence of creatine from our diet, as
occurs in strict vegetarians, results in suboptimal
muscle concentrations, indicating that our liver is not
capable of making all the creatine required for smoothly
functioning skeletal muscles.
Our body stores energy for later use within the
molecular phosphate bonds of ATP (adenosine
triphosphate) molecules. When energy is required, a
molecule of phosphorus is removed from ATP resulting in
ADP (adenosine diphosphate), phosphorus, and energy. ATP
is therefore similar to a battery in that it can supply
energy on demand. Approximately 60–70% of muscle
creatine is similarly phosphorylated, providing a second
source of energy storage.
As our skeletal muscles deplete their stores of ATP
during activity, the phosphocreatine molecules pass
their stored energy to ADP, resulting in a rapid
replenishment of ATP. The theory behind creatine
supplementation is that by increasing our stores of
phosphocreatine in skeletal muscle, more energy will
ultimately be available during periods of exercise.
Most research studies indicate that creatine
supplementation can improve performance in athletic
endeavors requiring the use of explosive force over a
period of a few seconds to a few minutes. The greatest
benefit is likely to be for sports such as weight
lifting, where repeated episodes of maximal exertion
occur over short periods of time. Creatine is probably
not beneficial to long duration aerobic exercises, such
as distance running, since these activities utilize
different biochemical pathways following depletion of
ATP stores. Furthermore, the effects of creatine
supplementation have been found to be highly variable
among individuals, with maximum performance boosts being
only about 5%.
Creatine does not directly promote increased muscle
mass, other than providing extra energy to possibly get
one more repetition. Initial weight gain with creatine
use is typically secondary to increased water retention
within skeletal muscle.
Short-term use of supplementary creatine within
recommended guidelines (loading phase of 20–25 grams a
day for 6 days, then 2 grams per day) is generally
considered to be safe. The effect of long-term use,
however, is unknown.
Dehydration is a potential problem, and one should be
sure to consume plenty of fluids during use of
supplemental creatine, especially during the hot summer
months. Most reports of adverse consequences associated
with its use have come from competitive wrestling, were
dehydration secondary to fluid restriction is common in
an effort to “make weight.”
It should also be noted that creatinine, a breakdown
product of creatine, is used by physicians to evaluate
renal function, as increased blood levels may indicate
varying degrees of kidney failure. If your doctor starts
talking about renal disease, be sure to tell him you are
taking supplemental creatine, or you may find yourself
in the middle of an expensive kidney disease work-up
that could include a renal biopsy (sampling of kidney
tissue).
In conclusion, although creatine is generally considered
to be one of the “safer” athletic dietary supplements,
unless you are in the top 1% of competitive athletes
competing in activities requiring explosive exercise,
you would be better served to improve performance
through skill development, sweat and improved diet.
Creatine is a very expensive way to get a small return
on performance.
If you’re not among the “best of the best,” the person you are
probably helping most is the chairman of the board of
the company who sold you the product in the first place.
Michael Nickels received an M.D. and a Ph.D. in
Biomedical Science (Microbiology and Immunology) from
the University of South Carolina School of Medicine.
