Creatine: Helpful for Sports Performance Enhancement
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.
Sources
Although some creatine exists in the daily diet, it is not an essential nutrient because your body can make it from the amino acids L-arginine, glycine, and L-methionine. Provided you eat enough animal protein (the principal source of these amino acids), your body will make all the creatine you need 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 3 to 4 days, followed by 2 to 5 g daily. Some authorities recommend skipping the loading dose. (By comparison, we typically get only about 1 g of creatine in the daily diet.)
Creatine’s ability to enter muscle cells can be increased by combining it with glucose, fructose, or other simple carbohydrates;1,2 in addition, prior use of creatine might enhance the sports benefits of carbohydrate-loading.3
Caffeine may block the effects of creatine.4
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 we have 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, rather than in studies involving athletes carrying out normal sports.5-10,70-72 It might also be helpful for resistance exercise (weight training), although not all studies have found benefit.34,35,55,57,61,73-74
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.11
Preliminary evidence suggests that creatine supplements may be able to reduce levels of triglycerides in the blood.12 (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;24,54,62 however, not all results have been positive.75
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.13,15-23,56,58,63,64,76,97,101,104
One study claimed to find evidence that creatine supplements can reduce levels of blood sugar.95 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 have tried it.14,15,20 However, these hopes were dashed in 2003 when the results of a 10-month, double-blind, placebo-controlled trial of 175 people with ALS were announced.59 Use of creatine at a dose of 10 g daily failed to provide any benefit at all in terms of symptoms or disease progression. Negative results were also seen in a subsequent, slightly smaller studies.65,106 Creatine also does not appear to strengthen muscles in people with wrist weakness due to nerve injury.77
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.60
Creatine has also shown some promise for improving mental function, particularly after sleep deprivation.78-79 However, in one small study, it showed no similar benefit in young adult subjects who were not sleep deprived.105
One study failed to find creatine helpful for maintaining muscle mass during treatment for colon cancer.80 Another study found little to no benefits in Parkinson’s disease,93 and another failed to find benefit in schizophrenia.98
What Is the Scientific Evidence for Creatine?
Exercise Performance
Several small double-blind studies suggest that creatine can improve performance in exercises that involve repeated short bursts of high-intensity activity.25,66
For example, a double-blind study investigated creatine and swimming performance in 18 men and 14 women.26 Men taking the supplement had significant increases in speed when doing six bouts of 50-meter swims starting at 3-minute intervals, as compared with men taking placebo. However, their speed did not improve when swimming 10 sets of 25-yard lengths started at 1-minute intervals. It may be that the shorter rest time between laps was not enough for the swimmers’ bodies to resynthesize phosphocreatine.
Interestingly, 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, 16 physical education students exercised 10 times for 6 seconds on a stationary cycle, alternating with a 30-second rest period.27 The results showed that individuals who took 20 g of creatine for 6 days were better able to maintain cycle speed. Similar results were seen in many other studies of repeated high-intensity exercise, although generally benefits are minimal in studies involving athletes engaged in normal sports rather than contrived laboratory tests.28-33,81-84
Isometric exercise capacity (pushing against a fixed resistance) also may improve with creatine, according to some, but not all studies.34,35,55,57,67,68,85-86
In addition, two double-blind, placebo-controlled studies, each lasting 28 days, provide some evidence that creatine and creatine plus HMB (beta hydroxymethyl butyrate) can increase lean muscle and bone mass.36 The first study enrolled 52 college football players during off-season training, and the other followed 40 athletes engaged in weight training.
However, studies of endurance or nonrepeated exercise have not shown benefits.37-40,87-88 Therefore, creatine probably won’t help you for marathon running or single sprints.69
High Triglycerides
A 56-day, double-blind, placebo-controlled study of 34 men and women found that creatine supplementation can reduce levels of triglycerides in the blood by about 25%.41 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 17 men with congestive heart failure who were given 20 g of creatine daily for 10 days.42 Exercise capacity and muscle strength increased in the creatine-treated group. Similarly, muscle endurance improved in a double-blind, placebo-controlled crossover study of 20 men with chronic heart failure.43 Treatment with 20 g of creatine for 5 days increased the amount of exercise they could complete before they reached exhaustion.
These results are promising, but further study is needed.44
Safety Issues
Creatine appears to be relatively safe.45 No significant side effects have been found with the regimen of several days of a high dosage (15 g to 30 g daily) followed by 6 weeks of a lower dosage (2 g to 3 g daily). A study of 100 football players found no adverse consequences during 10 months to 5 years of creatine supplementation.46 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.47,89, 94,96,99
Dividing the dose may help avoid gastrointestinal side effects (diarrhea, stomach upset, and belching). In one study of 59 male soccer players, two separate 5 g doses was associated with less diarrhea than a single 10 g dose.103
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.48,49 However, evidence suggests that creatine is safe for people whose kidneys are healthy to begin with, and who don’t take excessive doses.50,51,102 Furthermore, a 1-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.90 Nonetheless, prudence suggests that individuals with kidney disease, especially those on dialysis, should avoid creatine supplements.
Another concern revolves around the fact that creatine is metabolized in the body to the toxic substance formaldehyde.52 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.53
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.91
A few reports suggest that creatine could, at times, cause heart arrhythmias.92
As with all supplements taken in very high doses, it is important to purchase a high-quality form of creatine, as contaminants present even in very low concentrations could conceivably build up and cause problems.
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