Overview
Creatine is a naturally occurring substance that plays an important role in the production of energy in the body. The body converts it to phosphocreatine, a form of stored energy used by muscles.
Although the evidence for creatine is not definitive, it has the most evidence behind it among all the sports supplements. Numerous small double-blind studies suggest that it can increase athletic performance in sports that involve intense but short bursts of activity. The theory behind its use is that supplemental creatine can build up a reserve of phosphocreatine in the muscles to help them perform on demand. Supplemental creatine may also help the body make new phosphocreatine faster when it has been used up by intense activity.
Requirements and Sources
Although some creatine exists in the daily diet, it is not an essential nutrient because the human body can make it from the amino acids L-arginine, glycine, and L-methionine. Provided enough animal protein (the principal source of these amino acids) is consumed, the body will make all the creatine needed for good health.
Meat (including chicken and fish) is the most important dietary source of creatine and its amino acid building blocks. For this reason, vegetarian athletes may potentially benefit most from creatine supplementation.
Therapeutic Dosages
For bodybuilding and exercise enhancement, a typical dosage schedule starts with a loading dose of 15 to 30 g daily (divided into 2 or 3 separate doses) for three to four days, followed by 2 to 5 g daily. Some authorities recommend skipping the loading dose. (By comparison, humans typically get only about 1 g of creatine in their daily diet.)
Creatine’s ability to enter muscle cells can be increased by combining it with
glucose, fructose, or other simple carbohydrates; in
addition, prior use of creatine might enhance the sports benefits of
carbohydrate-loading. Caffeine may block the effects of
creatine.
Therapeutic Uses
Creatine is one of the best-selling and best-documented supplements for enhancing athletic performance, but the scientific evidence that it works is far from complete. The best evidence points to potential benefits in forms of exercise that require repeated short-term bursts of high-intensity exercise; this has been seen more in artificial laboratory studies, though, than in studies involving athletes during normal sports performance. It might also be helpful for resistance exercise (weight training), although not all studies have found benefit.
Creatine has also been proposed as an aid to promote weight loss and to reduce the proportion of fat to muscle in the body, but there is little evidence that it is effective for this purpose. Preliminary evidence suggests that creatine supplements may be able to reduce levels of triglycerides in the blood. (Triglycerides are fats related to cholesterol that also increase risk of heart disease when elevated in the body.) Creatine supplements might also help counter the loss of muscle strength that occurs when a limb is immobilized, such as following injury or surgery; however, not all results have been positive.
Studies, including small double-blind trials, inconsistently suggest that
creatine might be helpful for reducing fatigue and increasing strength in various
illnesses where muscle weakness occurs, including chronic obstructive pulmonary
disease (COPD), congestive heart failure, dermatomyositis, Huntington’s disease, McArdle’s
disease, mitochondrial illnesses, muscular dystrophy, and
myotonic
dystrophy.
One study claimed to find evidence that creatine supplements can reduce levels of blood sugar. However, because dextrose (a form of sugar) was used as the placebo in this trial, the results are somewhat questionable.
Evidence from animal and open human trials suggested that creatine improved strength and slowed the progression of amyotrophic lateral sclerosis (ALS), and for this reason, many people with ALS tried it. However, these hopes were dashed in 2003 when the results of a ten-month double-blind, placebo-controlled trial of 175 people with ALS were announced. Use of creatine at a dose of 10 grams (g) daily failed to provide any benefit in terms of symptoms or disease progression. Negative results were also seen in subsequent, slightly smaller studies. Creatine also does not appear to strengthen muscles in people with wrist weakness due to nerve injury.
Long-term use of corticosteroid drugs can slow a child’s
growth. One animal study suggests that use of supplemental creatine may help
prevent this side effect. Creatine has also shown some promise for improving
mental function, particularly after sleep deprivation. However, in one small
study, it showed no similar benefit in young adult subjects who were not
sleep-deprived.
One study failed to find creatine helpful for maintaining muscle mass during treatment for colon cancer. Another study found little to no benefits in Parkinson’s disease, and another failed to find any benefit in schizophrenia.
Scientific Evidence
Exercise performance. Several small double-blind studies suggest that creatine can improve performance in exercises that involve repeated short bursts of high-intensity activity. For example, a double-blind study investigated creatine and swimming performance in eighteen men and fourteen women. Men taking the supplement had significant increases in speed when doing six bouts of 50-meter swims starting at three-minute intervals, compared with men taking a placebo. However, their speed did not improve when swimming ten sets of 25-yard lengths started at one-minute intervals. It may be that the shorter rest time between laps was not enough for the swimmers’ bodies to resynthesize phosphocreatine.
None of the women enrolled in the study showed any improvement with the creatine supplement. The authors of this study noted that women normally have more creatine in their muscle tissue than men do, so perhaps creatine supplementation (at least at this level) is not of benefit to women, as it appears to be for men. Further research is needed to fully understand this gender difference in response to creatine.
In another double-blind study, sixteen physical education students exercised ten times for six seconds on a stationary cycle, alternating with a thirty-second rest period. The results showed that individuals who took 20 g of creatine for six days were better able to maintain cycle speed. Similar results were seen in many other studies of repeated high-intensity exercise, although benefits are generally minimal in studies involving athletes engaged in normal sports rather than contrived laboratory tests. Isometric exercise capacity (pushing against a fixed resistance) also may improve with creatine, according to some studies.
In addition, two double-blind, placebo-controlled studies, each lasting twenty-eight days, provide some evidence that creatine and creatine plus beta hydroxymethyl butyrate (HMB) can increase lean muscle and bone mass. The first study enrolled fifty-two college football players during off-season training, and the other followed forty athletes engaged in weight training.
However, studies of endurance or nonrepeated exercise have not shown benefits. Therefore, creatine probably will not help those running marathons or single sprints.
High triglycerides. A fifty-six-day double-blind, placebo-controlled study of thirty-four men and women found that creatine supplementation can reduce levels of triglycerides in the blood by about 25 percent. Effects on other blood lipids such as total cholesterol were insignificant.
Congestive heart failure. Easy fatigability is one unpleasant symptom of congestive heart failure. Creatine supplementation has been tried as a treatment for this symptom, with some positive results. A double-blind study examined seventeen men with congestive heart failure who were given 20 g of creatine daily for ten days. Exercise capacity and muscle strength increased in the creatine-treated group. Similarly, muscle endurance improved in a double-blind, placebo-controlled crossover study of twenty men with chronic heart failure. Treatment with 20 g of creatine for five days increased the amount of exercise they could complete before they reached exhaustion. These results are promising, but further study is needed.
Safety Issues
Creatine appears to be relatively safe. No significant side effects have been found with the regimen of several days of a high dosage (15 to 30 g daily) followed by six weeks of a lower dosage (2 to 3 g daily). A study of one hundred football players found no adverse consequences during ten months to five years of creatine supplementation. Contrary to early reports, creatine does not appear to adversely affect the body’s ability to exercise under hot conditions and might even be beneficial.
Dividing the dose may help avoid gastrointestinal side effects (diarrhea, stomach upset, and belching). In one study of fifty-nine male soccer players, administering two separate 5 g doses was associated with less diarrhea than a single 10 g dose.
However, there are some potential concerns with creatine. Because it is
metabolized by the kidneys, fears have been expressed that creatine supplements
could cause kidney injury, and there are two worrisome case reports. However,
evidence suggests that creatine is safe for people whose kidneys are healthy to
begin with and who do not take excessive doses. Furthermore, a one-year
double-blind study of 175 people with amyotrophic lateral sclerosis found that use
of 10 g of creatine daily did not adversely affect kidney function. Nonetheless,
prudence suggests that individuals with kidney disease, especially those on
dialysis, should avoid creatine supplements.
Another concern is that creatine is metabolized in the body to the toxic
substance formaldehyde. However, it is not clear whether the amount of
formaldehyde produced in this way will cause any harm. Three deaths have been
reported in individuals taking creatine, but other causes were most likely
responsible.
It has also been suggested that use of oral creatine would increase urine
levels of the carcinogen N-nitrososarcosine, but this does not seem to be the
case. A few reports suggest that creatine could, at times, cause heart
arrhythmias. As with all supplements taken in very high
doses, it is important to purchase a high-quality form of creatine, because
contaminants present even in very low concentrations could conceivably build up
and cause problems.
Bibliography
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Bemben, M. G., et al. “Creatine Supplementation During Resistance Training in College Football Athletes.” Medicine and Science in Sports and Exercise 33 (2001): 1667–73. Print.
Chilibeck, P. D., et al. “Effect of Creatine Ingestion After Exercise on Muscle Thickness in Males and Females.” Medicine and Science in Sports and Exercise 36 (2004): 1781–88. Print.
Cramer, J. T., et al. “Effects of Creatine Supplementation and Three Days of Resistance Training on Muscle Strength, Power Output, and Neuromuscular Function.” Journal of Strength Conditioning Research 21 (2007): 668–77. Print.
“Creatine.” MedlinePlus. US Natl. Lib. of Medicine, 24 June 2015. Web. 27 Jan. 2016.
Deacon, S. J., et al. “Randomized Controlled Trial of Dietary Creatine as an Adjunct Therapy to Physical Training in COPD.” American Journal of Respiratory and Critical Care Medicine 178 (2008): 133–39. Print.
Eckerson, J. M., et al. “Effect of Creatine Phosphate Supplementation on Anaerobic Working Capacity and Body Weight After Two and Six Days of Loading in Men and Women.” Journal of Strength Conditioning Research 19 (2005): 756–63. Print.
Kambis, K. W., and S. K. Pizzedaz. “Short-term Creatine Supplementation Improves Maximum Quadriceps Contraction in Women.” International Journal of Sport Nutrition and Exercise Metabolism 13 (2003): 97–111. Print.
Pluim, B. M., et al. “The Effects of Creatine Supplementation on Selected Factors of Tennis Specific Training.” British Journal of Sports Medicine 40 (2006): 507–11. Print.
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