Creatine: Physiological effects
Last modified: Thursday, 26. March 2009 - 5:15 am
Creatine is an ergogenic aid, increasing energy output for short, rapid bursts of muscle contractions (anaerobic exercise). More simply put, creatine recharges the muscles for activities requiring short, strong, and repetitive bursts of activity, such as sprints or weight lifting. It also minimizes muscle fatigue during contractions.
However, study results have been mixed as to exactly for which activities creatine has an ergogenic effect. For example, studies involving stationary cycle sprints have demonstrated positive performance enhancing results for creatine, but it is still unknown whether these results can be consistently reproduced in actual competition outside of the laboratory. In addition, some cycling studies have not shown any significant benefit to creatine supplementation.
The literature does reach a consensus on one point — creatine does not enhance aerobic activity, which is required in endurance sports such as cross-country running, basketball, or long-distance cycling. However, to the extent that these sports may require short bursts of activity, such as sprints at the end of a cycling or running race, creatine may offer athletes some performance gains.
Creatine supplementation causes rapid weight gain, mostly likely via water retention by skeletal muscles. The typical weight gain during the loading period of creatine supplementation is \-A lb (0.45-1.8 kg). Whether this weight gain comes from water retention, an increase of lean body mass, or a combination of both has not been conclusively established. Research has shown that individuals taking creatine urinate less during the first several days of the loading dose period, which may support the water retention theory. Further studies are again needed to determine the exact mechanisms by which creatine increases overall weight.
Once creatine phosphate is metabolized, it is converted to creatinine, a waste product, which is cleared from the bloodstream by the kidneys. Excess free creatine (or creatine unbound to phosphate) is also cleared from the body this way. Elevated serum (or blood) creatinine levels of over 1.2 mg/dL for women and 1.4 mg/dL for men may indicate the onset of kidney disease. Anyone taking creatine supplements for therapeutic or athletic purposes should do so under a doctor’s care. Regular serum creatinine tests may be recommended for these individuals to monitor their kidney function.
Anyone with existing kidney disease, or with health conditions that put them at high risk for kidney problems (such as diabetes) should avoid creatine supplements.
Pregnant women, women who breastfeed, and children and adolescents under 18 years of age should avoid creatine use, as its long-term effect on these populations has not been adequately studied. Individuals with chronic medical conditions should consult with their healthcare professional before taking creatine or any other dietary supplement.
Harmful side effects
Some athletes using creatine supplements for training have reported muscle cramping and gastrointestinal distress (i.e., diarrhea, stomach cramps, vomiting), particularly with loading doses. At this time, all reports are anecdotal, which means that they are reported by individual users or healthcare providers but have not been conclusively proven through clinical research or controlled studies.
Creatine supplementation causes water retention by muscle tissue, which may be the source of muscle cramps. It has also been theorized that athletes who experience this side effect have a fluid or electrolyte imbalance due to dehydration. In some cases, adequate water intake may eliminate the muscle cramping.
As of early 2002, controlled clinical studies had not discovered any direct link between creatine use and muscle pain or strains when supplements are taken according to generally accepted guidelines. In fact, preliminary results from an Arkansas State University study of college baseball players found that those who used creatine did not have any more cramping or muscle injuries than non-supplementing players.
Gastrointestinal side effects, such as nausea, vomiting, diarrhea, and stomach cramps, have also not been conclusively linked to creatine supplements that are taken following generally accepted guidelines. The practice of taking creatine during or immediately prior to a workout has been found to cause gastrointestinal distress after exercise, as has taking creatine with large amounts of sugar or glucose, which has a tendency to slow digestion. Neither of these Ingestion methods is recommended by the American College of Sports Medicine. Further controlled clinical studies are needed to determine the mechanisms and prevalence of these side effects.
The Special Nutritionals Adverse Event Monitoring System (SN/AEMS) of the U.S. Food and Drug Administration (FDA), a database of consumer reactions to nutritional supplements and substances, has had 31 reports of adverse reactions to products containing creatine between 1993-1998. Reported symptoms include (but were not limited to):
• shortness of breath
• irregular heartbeat
Some of the SN/AEMS incidents involved creatine monohydrate that was mixed with or taken with other supplements and substances, so it is difficult to determine to what extent creatine played a role in these reactions. There have also been anecdotal case reports of hypertension (high blood pressure) and elevated liver enzymes in athletes taking creatine supplements.
Dehydration may also be a risk for creatine users. Creatine causes skeletal muscle to absorb intercellular fluid from bodily tissues and into the muscle where it is retained. For this reason, athletes who are already losing fluid during physical activity may be further dehydrated by creatine supplementation.
In addition, muscle can only absorb up to 160 mmol/kg of creatine. All excess dietary and supplemental creatine must be excreted out of the body, which can increase urinary output and put undue stress on the kidneys.
There have also been published reports of fatalities in individuals using creatine monohydrate. During November and December of 1997, three collegiate wrestlers in three different states died during training to “make weight” for upcoming wrestling meets. Although there was initially widespread media speculation that creatine played a major role in their sudden deaths, it was later determined by the U.S. Centers for Disease Control (CDC) that the fatalities were directly attributable to severe hyperthermia (overheating, or heat exhaustion) and dehydration. All three had been attempting rapid weight loss by “sweating off’ the pounds, wearing rubber suits to undertake a strenuous workout regimen, and refusing adequate fluid intake.
Although the CDC did not cite creatine use as a factor in these dehydration-related deaths, the American College of Sports Medicine (ACSM) notes that preliminary clinical evidence indicates that creatine does appear to affect fluid balance in athletes. In a consensus statement on the use of creatine supplementation, the ACSM has said that “The potential acute effects of high-dose creatine supplementation on body fluid balance has not been fully investigated, and ingestion of creatine before or during exercise is not recommended.” The ACSM also recommends that creatine supplementation should be avoided by anyone exercising or participating in sports in extremely high temperatures due to the dehydration risk.
Because creatine is regulated by the FDA as a dietary supplement and not a drug, the purity of the product is a concern. A test of 100 popular nutritional supplements conducted by the International Olympic Committee (IOC) at the German Sports University in Cologne found that 16 were adulterated with nandrolone, a steroid. Nandrolone was not a listed ingredient on the product label, and most of the creatine products tested originated in the United States.
In other independent tests, ConsumerLab.com, a privately held U.S. company that specializes in laboratory analysis of nutritional and herbal supplements for purity, strength, and truth in labeling, found that 15% of creatine supplements tested did not meet industry standards for creatine content, purity, and label claims.
Long-term health effects
The data on the long-term health effects of creatine supplementation is extremely limited. However, at least one animal study has found that creatine caused a decline in kidney function in rats with existing renal (kidney) disease. In addition, published case reports have indicated that creatine can cause further renal impairment in people with pre-existing kidney disease. However, several studies of healthy athletes have shown that both short-term and extended creatine supplementation had no effect on kidney function.
Creatine is not recommended for use by individuals with kidney problems, or by anyone at risk for kidney disease (such as those with a family history of kidney problems or diabetes). Again, further controlled clinical studies are needed to determine the long-term impact and safety of creatine supplement use on human renal function.
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