Creatine Monohydrate

One of the most controversial concerns involving creatine supplementation is its effect on renal function. Creatine supplementation can cause an increase in urinary creatinine excretion, which is often used as an indicator of kidney function. However, this increase correlates well with the increase in muscle creatine that is observed during supplementation and reflects the increased rate of muscle creatine degradation to creatinine rather than any abnormality of renal function. Pritchard recently reported on adverse effects associated with creatine supplementation in an isolated case involving presence of kidney disease. However, other studies have shown normal kidney function in creatine-supplemented healthy individuals. Normally, creatine does not exit muscle cells until it has degraded to creatinine in an irreversible reaction involving the loss of a water molecule from the creatine molecule itself. Following its formation, creatinine diffuses from skeletal muscle and is excreted by the kidneys.

Poortmans recently reported on five healthy men ingesting either a placebo or 20g of creatine per day for 5 consecutive days. In their study, blood samples and urine collections were analyzed for creatine and creatinine concentrations after each experimental session. Total protein and albumin urine excretion rates were also determined. Oral creatine supplementation had a significant incremental impact on arterial content (3.7 -fold) and urine excretion rate (90-fold) of this compound. In contrast, arterial and urine creatinine values were not affected by creatine ingestion. The glomerular filtration rate (creatinine clearance) and the total protein and albumin excretion rates remained within the normal range.

In one of the most recent studies, Poortmans et al. examined creatinine, urea, and plasma albumin clearances in individuals supplemented with creatine as well as placebo from 10 months to 5 years. During this trial, no statistical differences were found between the control group and the creatine group in plasma concentration and urine excretion rates for creatinine, urea, or albumin. Glomerular filtration rate, tubular reabsorption, and glomerular membrane permeability were normal in both groups. Therefore, it is becoming increasingly apparent that neither short-term, medium-term, nor long-term oral creatine supplementation induces detrimental effects on kidney function in healthy individuals. Whether creatine is safe for patients who suffer from renal dysfunction has yet to be determined, indicating the need for more research in this area.