While creatine helps athletes and bodybuilders build lean muscle mass in the gym, questions have existed about possible side effects. One issue is creatine’s effect on the kidneys, but medical experts generally downplay any link between creatine ingestion and kidney problems. However, doctors advise individuals with a history of kidney disease to refrain from using creatine. Also, since creatine only became popular as a supplement within the last 15 to 20 years, there have been no studies on the long-term effects.
Creatine works by getting absorbed into your muscles and helping your muscles perform high-intensity anaerobic exercises such as weightlifting. Most of the creatine ends up in your urine, leading to about 25 percent more urine than normal on a daily basis. Excess urine can put a strain on the kidneys by forcing them to do more work than usual, setting up the potential for kidney damage.
The best-known studies on creatine’s effect on the kidneys have revealed little reason for alarm. In 2003, Dr. Richard Kreider of the Exercise & Sport Nutrition Laboratory at the University of Memphis examined creatine’s effect on 98 NCAA Division I college athletes. The study found no significant difference in the blood and urine samples of athletes who had been using creatine for 12 to 21 months and the samples of nonusers. Other studies have turned up similar results.
The primary cause for concern with creatine use is in patients with a history of kidney problems. One study involved rats with cystic kidney disease and showed that creatine supplementation resulted in greater cyst growth and had an adverse effect on overall kidney function. The labels on creatine containers suggest consulting a doctor before using creatine if you have impaired kidney function or take any medications that could affect kidney function.
You should follow the dosage suggestions on the bottle when taking creatine for any period of time. The New England Journal of Medicine in 1999 reported on an otherwise-healthy athlete who had developed kidney problems after taking creatine. The athlete had consumed 20 g a day over a 4-week period. Creatine manufacturers generally suggest taking 15 to 20 g a day during the first week-- typically known as the “loading phase”--and then taking 5 to 15 g for the next 3 weeks while continually drinking plenty of water. Beyond 4 weeks, manufacturers suggest limiting consumption to 5 g daily.
In part because of the lack to date of long-term studies about creatine use, including its effect on the kidneys, the American College of Sports Medicine has advised against creatine supplementation for anyone under 18. On the other hand, the International Society of Sports Nutrition has mentioned creatine as a viable alternative to steroids or other performance-enhancing drugs that are illegal or possibly dangerous for high school athletes. The ISSN does recommend that parents supervise their kids’ creatine use.