As a Nephrologist, I probably talk about creatinine about 20 times a day. Creatinine is a metabolite measured in the blood that is used as a marker for kidney function. The level of creatinine in the blood can designate how someone’s kidney is filtering.
Most referrals that I get from Internists are for an elevated blood creatinine in a patient. Kidneys normally filter creatinine from the blood and keep the level under 1 mg/dl. If the blood creatinine level rises, it usually is a depiction of a low kidney function.
Creatine versus creatinine
Creatinine is a good marker, and a convenient one, to estimate someone’s kidney function. It is made by the muscle and is filtered freely through the tubules (specialized cells) of the kidney.
Creatine on the other hand, is a supplement that is available as a powder and is commonly used by bodybuilders to gain muscle mass. Creatine powder is generally recognized as safe based on some studies done in sports nutrition and there are plenty of anecdotal studies that have shown that creatine supplements can help gain weight (as muscle) with regular use.
Supplementation of creatine, e.g. using creatine monohydrate powder, also supports muscle protein repair and regeneration. Creatine is then converted to creatinine which is stored in the muscle cells as creatinine phosphokinase (or CPK).
Benefits of creatine supplementation in athletes- what’s the data?
Creatine monohydrate is commonly used both before and after work out for performance enhancement, although, at least with short term use in competitive sports such as cycling and running, its efficacy as a performance “booster” is questionable (1,2). The small benefit of creatine supplement has been presumed to be as a result of the gain in muscle strength. But its frequent use by the bodybuilding community has led people to ask the fundamental question- is creatine safe?
Studies done in the 1990s-2000s have also shown that creatine monohydrate, consumed on a regular basis for long term is generally without significant side effects and does allow for gains in lean muscle mass (3). And more mass, in some athletics, can amount to more power.
A randomized control trial done by Groeneveld et al in patients with amyotrophic sclerosis (who have muscle wasting) showed that creatine tolerance over one year was similar in patients who received up to 10 grams per day, as in those who received placebo. In this particular study, creatine monohydrate was not associated with kidney damage as tested by blood and urine markers.
A generally safer dose of creatinine has been recognized as under 3 grams per day in divided doses. Most of these studies have been carried out with creatine monohydrate, the most abundantly available supplement in the market.
Safety data on higher doses of creatine supplementation (15-20 grams/day) gets more murky. Doses generally above 5 grams per day for an extended period of time may cause problems in certain individuals who may be predisposed to kidney problems. Creatine in higher doses can cause GI side effects such as nausea or diarrhea and may not be well tolerated.
Can creatine cause kidney damage?
As Nephrologists, we get this question often. As discussed above, a dose of less than 3 grams/day is generally recognized as safe and is supported by some clinical studies (4). However, a case report in 2006 uncovered an episode of kidney failure in a young adult with more than 20 grams per day of creatine consumption for an extended period of time (5). Such reports, although not widespread, do warrant a detailed analysis of the safety profile of this supplement, particularly in vulnerable groups who consume it for a long duration.
Can creatine elevate blood creatinine levels?
In individuals who gain a significant amount of muscle mass, creatinine levels in the blood are proportionately on the higher side. Hence, it is uncertain if this rise in creatinine is purely from an overproduction of this molecule, or from its impaired ability to be excreted by the kidney.
Since creatinine in the blood is used to estimate kidney function, a rise in its level in the blood can sometimes label an individual as someone having kidney disease. This is not entirely true for the reasons discussed above. It is possible that creatine causes a rise in blood creatinine without causing direct kidney injury.
In fact, a detailed analysis by Pline et al in 2005 answered this very question (6). This group looked at numerous studies conducted from 1995-2005 that addressed creatine supplementation and kidney function. They found that both, short term (5 days) and long term (up to 5 years) consumption of creatine supplements was not associated with significant kidney damage in either group. They also noted that the rise in blood creatinine levels after consumption of creatine monohydrate supplement was relatively small within the 5 day period.
In an individual suspected to have kidney problems, additional tests can shed more light. These tests typically involve a 24-hour urine collection or using additional kidney injury markers such as cystatin C. Doctors need to take into account that individual’s additional medical history before making such a diagnosis. An ultrasound of the kidneys and urine tests to detect protein may be required.
The bottom line
Creatine in low doses may be safe and allow young adults to gain muscle mass. However, in higher doses especially when it is used over a long period, the safety of creatine supplements may be questionable and more data is needed, particularly in adolescents and the elderly. Individuals need to weigh in the risks versus benefits before using creatine.
Despite its widespread use and fame in the bodybuilding community, the data on its efficacy and potency is not supported completely by clinical studies. While it may help build muscle mass, whether it can affect performance (e.g. running, swimming) in competitive sports is still doubtful.
REFERENCES
Effects of oral creatine supplementation on multiple sprint cycle performance. C Barnett , M Hinds, D G Jenkins. Aust J Sci Med Sport 1996 Mar;28(1):35-9.
The effects of oral creatine supplementation on performance in single and repeated sprint swimming. M C Peyrebrune , M E Nevill, F J Donaldson, D J Cosford. J Sports Sci . 1998 Apr;16(3):271-9.
Few adverse effects of long-term creatine supplementation in a placebo-controlled trial. G J Groeneveld C Beijer, J H Veldink, S Kalmijn, J H J Wokke, L H van den Berg. Int J Sports Med 2005 May;26(4):307-13.
Effects of creatine supplementation on renal function. Wyndie M Yoshizumi , Candy Tsourounis. J Herb Pharmacother 2004;4(1):1-7.
Acute renal failure in a young weight lifter taking multiple food supplements, including creatine monohydrate. Thorsteinsdottir B, Grande JP, Garovic VD. J Ren Nutr. 2006 Oct;16(4):341-5.
The effect of creatine intake on renal function. Kurt A Pline , Curtis L Smith. Ann Pharmacother. 2005 Jun;39(6):1093-6.
Dr. Kharait is an MD and a practicing Nephrologist in Northern California. He completed his Residency in Internal Medicine and Fellowship in Nephrology from the University of California, San Francisco. He has a PhD in Molecular Physiology from the University of Pittsburgh and specializes in treating patients with electrolyte disorders and kidney diseases.
