title: Creatine metabolism and safety profiles after six-week oral guanidinoacetic acid administration in healthy humans.
abstract: OBJECTIVE
  Guanidinoacetic acid (GAA) is a natural precursor of creatine, yet the potential use of GAA as a nutritional additive for restoring creatine availability in humans has been limited by unclear efficacy and safety after exogenous GAA administration. The present study evaluated the effects of orally administered GAA on serum and urinary GAA, creatine and creatinine concentration, and on the occurrence of adverse events in healthy humans.
  
  
  RESULTS
  Twenty-four healthy volunteers were randomized in a double-blind design to receive either GAA (2.4 grams daily) or placebo (PLA) by oral administration for 6 weeks.
  
  
  BACKGROUND
  www.clinicaltrials.gov, identification number NCT01133899. Serum creatine and creatinine increased significantly from before to after administration in GAA-supplemented participants (P < 0.05). The proportion of participants who reported minor side effects was 58.3% in the GAA group and 45.5% in the placebo group (P = 0.68). A few participants experienced serum creatine levels above 70 µmol/L.
  
  
  CONCLUSIONS
  Exogenous GAA is metabolized to creatine, resulting in a significant increase of fasting serum creatine after intervention. GAA had an acceptable side-effects profile with a low incidence of biochemical abnormalities.
authors: Center for Health, Exercise and Sport Sciences, Belgrade, Serbia. sergej.ostojic@chess.edu.rs
authors: Sergej M
authors: SM
authors: Ostojic
authors: Barbara
authors: B
authors: Niess
authors: Marko
authors: M
authors: Stojanovic
authors: Milos
authors: M
authors: Obrenovic
mesh_terms: D000284:Administration, Oral; D000328:Adult; D003401:Creatine / Q000097:blood*; D003404:Creatinine / Q000097:blood*; D019587:Dietary Supplements / Q000009:adverse effects; D005260:Female; D005998:Glycine / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives*; D006801:Humans; D008297:Male
chemical_list: D003404:Creatinine; C004946:glycocyamine; D003401:Creatine; D005998:Glycine
keywords: Clinical markers.; Creatine synthesis; Creatinine