Creatine Study

None — Creatine

Creatine is a compound made by the body from amino acids and produced mainly in the liver. It's then carried by the blood to the skeletal muscles, where it's stored in the form of creatine phosphate. During short bouts of high-intensity exercise, creatine phosphate is converted into adenosine triphosphate (ADT), a major source of energy for the muscles.

Since creatine provides energy to the muscles during exercise, some athletes take creatine supplements. The goal of supplementation is to enhance performance. However, studies on the benefits of creatine supplements for sports performance have mixed results, especially when used in high doses. The National Institutes of Health reports 25 percent of professional baseball players and nearly 50 percent of professional football players use creatine supplements. Use is also common among high school athletes.

Creatine and the Kidneys

When the skeletal muscles need extra energy, metabolism of creatine leads to a waste product, called creatinine. The creatinine is carried by the blood to the kidneys, where it is filtered out and eliminated through the urine. By measuring the amount of creatinine in the blood and urine, doctors can determine how well the kidneys are functioning. For adult males, the normal levels of creatinine in the blood are about 0.6 to 1.2 milligrams per deciliter (mg/dL). In adult females, the normal levels range from about 0.5 to 1.1 mg/dL.

When the kidneys aren't working as well as they should, the level of creatinine in the blood rises (because the kidneys aren't able to efficiently remove the waste product). A blood creatinine level of 10 or more in adults can be an indication of severe kidney impairment. If this happens, the patient may need kidney dialysis (artificial blood filtration using a machine) to clear waste products from the blood.

Creatine Supplements and the Kidneys

While creatine supplements are generally recognized as safe, use can cause an elevation in creatinine levels. Researchers at Beth Israel Medical Center in New York City wanted to study and compare the effects of two creatine supplements: creatine monohydrate and creatine ethyl ester. Participants in the study were 25 healthy men and women aged 23 to 41. The participants were randomly assigned to take an oral form of either creatine monohydrate or creatine ethyl ester. Levels of creatinine were then measured several times over the next few hours. Another measurement was taken 24 hours after the dose. The study was repeated one month later with participants switching to the other form.

The investigators found when the participants took creatine monohydrate, the creatinine levels were only slightly elevated, to about 2 mg/dL (up from the normal of about 1 mg/dL). For those who took the creatine ethyl ester, creatinine levels ranged from 8 to 10 mg/dL. Normally, this would be an indication of serious kidney problems. However, after 24 hours, creatinine levels returned to normal, indicating the elevation was solely associated with ingestion of creatine ethyl ester.

Kristopher Hunt, M.D., Chief Resident of Emergency Medicine, says the study shows people who take creatine supplements need to tell their physicians about their use. If the doctor is not aware the patient is taking the supplements, elevated levels of creatinine may lead to unnecessary further testing and, in some cases, putting the patient on kidney dialysis.

Hunt says the study only looked at a single dose of creatine supplements and the effect of long-term use on creatinine levels isn't known. He also says that the high levels of creatinine after taking creatine ethyl ester probably means the body is breaking down that form too rapidly and, thus, it may provide little benefit for the muscles.

For information on creatine:

For information on the creatinine clearance test, click here.

The FDA has general information on safe use of dietary supplements here.

WSOC