Background. Creatine is widely used as an ergogenic substance among athletes. Safety of prolonged creatine intake has been questioned, based upon case reports and animal data. We investigated the effect of prolonged creatine ingestion on renal function in animals with normal kidney function or preâ€existing kidney failure, respectively.
Methods. Male Wistar rats were randomly allocated to four experimental groups: (i) shamâ€operated, control diet; (ii) shamâ€operated, creatineâ€supplemented diet (2% w/w (0.9±0.2 g creatine/kg body weight/day)); (iii) twoâ€thirds nephrectomized, control diet; and (iv) twoâ€thirds nephrectomized, creatine supplemented diet. Glomerular filtration rate was determined using inulin and creatinine clearance, together with albumin excretion, urea clearance, muscle and serum creatine and serum cystatin C concentrations.
Results. In contrast to previous reports, no detrimental effects of creatine supplementation on the renal function indices were observed in twoâ€thirds nephrectomized or shamâ€operated animals. No differences were observed in inulin (0.28±0.08 vs 0.25±0.08 ml/min/100 g; P=NS) or creatinine clearance rates. Serum cystatin C concentration, urinary protein excretion, and albumin and urea clearance were comparable between creatineâ€supplemented and controlâ€diet fed animals in both shamâ€operated and twoâ€thirds nephrectomized animals. Serum creatine and intramuscular total creatine concentrations were higher in creatineâ€supplemented groups (P<0.05).
Conclusions. Creatine supplementation at a dosage of 2% w/w for 4 weeks does not impair kidney function in animals with preâ€existing renal failure or in control animals.