Study Overview
Wyss and Kaddurah-Daouk (2000) published a key thorough review in Physiological Reviews covering the complete biochemistry, physiology, and pathology of the creatine-creatinine system.
This 90-page review remains one of the most thorough treatments of creatine metabolism in the scientific literature, covering endogenous synthesis, dietary intake, cellular transport, the creatine kinase reaction, creatinine formation, and the relevance of this system to various diseases (Wallimann et al., 2011) .
Key Findings
- Two-organ synthesis: Creatine synthesis requires cooperation between the kidneys (which produce the precursor guanidinoacetate via AGAT) and the liver (which converts guanidinoacetate to creatine via GAMT). This two-organ system uses approximately 40% of all S-adenosylmethionine (SAM) produced by the body
- Creatine transporter is essential: The SLC6A8 creatine transporter is required for cellular creatine uptake. Mutations in this transporter cause creatine deficiency syndromes with severe neurological consequences, underscoring creatine’s importance for brain function
- Creatinine is an irreversible endpoint: The conversion of creatine to creatinine is non-enzymatic, irreversible, and occurs at a constant rate (~1.7%/day). This continuous loss means the body must constantly replenish creatine through synthesis and diet
- Creatine kinase system is multifunctional: Beyond simple energy buffering, the creatine kinase system serves as an energy shuttle, pH buffer, and metabolic signal integrator across cells
- Disease relevance: Disruptions in creatine metabolism are implicated in numerous conditions including inborn errors of creatine synthesis, neurodegenerative diseases, and muscle wasting disorders
Practical Implications
This thorough review provides the biochemical foundation for understanding why creatine supplementation works and why it is needed.
The key practical insight is that the body loses approximately 2g of creatine daily through irreversible creatinine conversion.
This must be replaced through a combination of endogenous synthesis (~1-2g/day) and dietary intake (~1-2g/day from meat and fish).
For Malaysian vegetarians or those with low meat intake, dietary creatine may be insufficient to fully replenish daily losses, making supplementation particularly valuable.
The 3-5g/day recommendation provides a comfortable surplus above daily losses, ensuring muscle creatine stores remain at or near saturation.
The clinical implication of elevated creatinine from supplementation is important for Malaysian healthcare: doctors should be aware that patients taking creatine will show elevated serum creatinine that does not indicate kidney disease.
This is particularly relevant in Malaysia’s public healthcare system where routine blood tests may flag elevated creatinine (Kreider et al., 2017) .
Study Limitations
- As a thorough review rather than original research, it synthesises rather than generates new data
- Some areas discussed were still poorly understood at the time of publication and have since been updated
- The review predates many of the clinical trials on creatine supplementation in special populations
- Some of the disease associations discussed were speculative and have not been fully confirmed by subsequent research
- The focus on biochemistry means practical supplementation recommendations are limited
Where This Fits in the Evidence
Wyss and Kaddurah-Daouk’s work is a reference text rather than a result: a roughly 90-page mapping of how the body synthesises, transports and loses creatine, published in Physiological Reviews. Its lasting practical value is conceptual — by establishing that creatinine is the fixed, irreversible endpoint of the creatine pool, it explains why supplementation nudges up serum creatinine without signalling any kidney damage, a point that still trips up routine blood tests. It defines the biochemistry that later supplementation and safety trials build on rather than testing supplementation itself. Those trials and reviews are gathered in our research library.
Sources & References
This page summarises Wyss M, Kaddurah-Daouk R. Creatine and creatinine metabolism. Physiological Reviews. 2000;80(3):1107-1213.