Does long-term creatine supplementation impair kidney function in resistance-trained individuals consuming a high-protein diet?
Rebeca Lugaresi Journal of the International Society of Sports Nutrition 2013, 10:26

Background
The aim of this study was to determine the effects of creatine supplementation on kidney function in resistance-trained individuals ingesting a high-protein diet.
Methods
A randomized, double-blind, placebo-controlled trial was performed. The participants were randomly allocated to receive either creatine (20 g/d for 5 d followed by 5 g/d throughout the trial) or placebo for 12 weeks. All of the participants were engaged in resistance training and consumed a high-protein diet (i.e., >= 1.2 g/Kg/d). Subjects were assessed at baseline (Pre) and after 12 weeks (Post). Glomerular filtration rate was measured by 51Cr-EDTA clearance. Additionally, blood samples and a 24-h urine collection were obtained for other kidney function assessments.
Results
No significant differences were observed for 51Cr-EDTA clearance throughout the trial (Creatine: Pre 101.42 +/- 13.11, Post 108.78 +/- 14.41 mL/min/1.73m2; Placebo: Pre 103.29 +/- 17.64, Post 106.68 +/- 16.05 mL/min/1.73m2; group x time interaction: F = 0.21, p = 0.64). Creatinine clearance, serum and urinary urea, electrolytes, proteinuria, and albuminuria remained virtually unchanged.
Conclusions
A 12-week creatine supplementation protocol did not affect kidney function in resistance-trained healthy individuals consuming a high-protein diet; thus reinforcing the safety of this dietary supplement.

hort review on creatine–creatine kinase system in relation to cancer and some experimental results on creatine as adjuvant in cancer therapy
Subrata Patra, Alok Ghosh, Soumya Sinha Roy, Soumen Bera, Manju Das, Dipa Talukdar, Subhankar Ray, Theo WallimannetManju Ray
Amino Acids Volume 42, Number 6 (2012), 2319-2330

The creatine/creatine kinase (CK) system plays a key role in cellular energy buffering and transport. In vertebrates, CK has four isoforms expressed in a tissue-specific manner. In the process of creatine biosynthesis several other important metabolites are formed. The

anticancer effect of creatine had been reported in the past,

and recent literature has reported low creatine content in several types of malignant cells. Furthermore,

creatine can protect cardiac mitochondria from the deleterious effects of some anticancer compounds.

Previous work from our laboratory showed progressive decrease of phosphocreatine, creatine and CK upon transformation of skeletal muscle into sarcoma. It was convincingly demonstrated that prominent expression of creatine-synthesizing enzymes l-arginine: glycine amidinotransferase and N-guanidinoacetate methyltransferase occurs in sarcoma, Ehrlich ascites carcinoma and sarcoma 180 cells; whereas, both these enzymes are virtually undetectable in skeletal muscle. Creatine transporter also remained unaltered in malignant cells. The anticancer effect of methylglyoxal had been known for a long time. The present work shows that this

anticancer effect of methylglyoxal is significantly augmented in presence of creatine.

On creatine supplementation the effect of methylglyoxal plus ascorbic acid was further augmented and there was no visible sign of tumor.

Moreover, creatine and CK, which were very low in sarcoma tissue, were significantly elevated with the concomitant regression of tumor.

Effect of Different Frequencies of Creatine Supplementation on Muscle Size and Strength in Young Adults
Journal of Strength & Conditioning Research: July 2011 - Volume 25 - Issue 7 - pp 1831-1838

The purpose was to determine if creatine supplementation, consumed immediately before and immediately after exercise, with different dosing frequency (i.e., 2 or 3 d wk−1) could enhance the gains in muscle size and strength from resistance training (RT) in young adults. A group of 38 physically active, nonresistance trained university students (21-28 years) was randomly allocated to 1 of 4 groups: CR2 (0.15 g·kg−1 creatine during 2 d wk−1 of RT; 3 sets of 10 repetitions; n = 11, 6 men, 5 women), CR3 (0.10 g·kg−1 creatine during 3 d wk−1 of RT; 2 sets of 10 repetitions; n = 11, 6 men, 5 women, PLA2 (placebo during 2 d wk−1 of RT; n = 8, 5 men, 3 women), and PLA3 (placebo during 3 d wk−1 of RT; n = 8, 4 men, 4 women) for 6 weeks. Before and after training, measurements were taken for muscle thickness of the elbow and knee flexor and extensor muscle groups (ultrasound), 1-repetition maximumleg press and chest press strength, and kidney function (urinary microalbumin). Repeated-measures analysis of variance showed that strength and muscle thickness increased in all groups with training (p < 0.05). The CR2 (0.6 ± 0.9 cm or 20%; p < 0.05) and CR3 groups (0.4 ± 0.6 cm or 16.4%; p < 0.05) experienced greater change in muscle thickness of the elbow flexors compared to the PLA2 (0.05 ± 0.5 cm or 2.3%) and PLA3 groups (0.13 ± 0.7 cm or 6.3%). Men supplementing with creatine experienced a greater increase in leg press strength (77.3 ± 51.2 kg or 62%) compared to women on creatine (21.3 ± 10 kg or 34%, p < 0.05). We conclude that creatine supplementation during RT has a small beneficial effect on regional muscle thickness in young adults but that giving the creatine over 3 d wk−1 did not differ from giving the same dose over 2 d wk−1.