Poortmans & Francaux 2000: Creatine Does Not Impair Kidney Function — Study Summary

Study Overview

Poortmans and Francaux (2000) published an observational study in Medicine and Science in Sports and Exercise that directly addressed one of the most persistent concerns about creatine supplementation — its effect on kidney function. The study monitored 175 healthy athletes who had been using creatine for periods ranging from 10 months to 5 years, assessing key markers of renal health (JR & M, 2000) .

Key Findings

• No adverse effects on renal function: After up to 5 years of creatine supplementation, no participant showed signs of kidney impairment
• GFR remained normal: Glomerular filtration rate, the gold-standard measure of kidney function, stayed within healthy ranges throughout the study
• Plasma creatinine stayed within normal limits: While creatine supplementation naturally raises creatinine levels slightly (creatinine is a breakdown product of creatine), values remained within the normal clinical range
• Urinalysis normal: No abnormalities were detected in urine composition, further confirming kidney health
• Safe at recommended doses: The study concluded that creatine supplementation at standard recommended doses does not impair renal function in healthy individuals

Practical Implications

This study provides strong reassurance for anyone concerned about the kidney safety of creatine. The myth that creatine damages kidneys likely stems from a misunderstanding: creatine does raise serum creatinine levels slightly, and elevated creatinine is often used as a marker for kidney disease. However, in the context of creatine supplementation, this elevation is expected and benign — it reflects increased creatine metabolism, not kidney damage. For healthy individuals, taking 3 to 5g of creatine monohydrate daily is well-supported as safe for the kidneys, even over periods of years. That said, individuals with pre-existing kidney disease should consult their doctor before supplementing, as most safety studies have been conducted in individuals with healthy kidneys.

Study Limitations

• Observational design means this is not a randomized controlled trial — there was no placebo group for direct comparison
• All participants were healthy athletes, so results may not apply to individuals with pre-existing kidney conditions
• Self-reported supplementation duration and dosing introduces potential inaccuracy
• The study did not include very elderly populations or those with comorbidities
• While 175 participants is a reasonable sample, larger epidemiological studies would further strengthen the conclusions

Study Design and Methodology

Understanding how a study was designed helps assess the strength of its conclusions. Key methodological factors to evaluate include:

• Sample size — larger studies (n=50+) provide more reliable results than small studies (n=10-15). Small sample sizes increase the risk of false positives and limit the ability to detect moderate effect sizes
• Study duration — creatine research requires adequate duration for muscle saturation (minimum 4 weeks for maintenance dosing, 1 week for loading). Studies shorter than this may miss the full effect
• Blinding — double-blind, placebo-controlled designs (where neither researchers nor participants know who receives creatine) are the gold standard for minimising bias
• Population studied — results from trained athletes may not fully apply to untrained individuals, and vice versa. Age, sex, and dietary habits (particularly vegetarian status) also influence creatine response
• Outcome measures — direct measures (muscle biopsy, MRS imaging) are more informative than indirect proxies (blood markers, performance tests) for assessing creatine uptake and metabolism

Clinical Implications and Practical Relevance

This research contributes to our understanding of creatine in several practical ways:

For athletes and fitness enthusiasts: The findings support the use of creatine monohydrate as a safe, effective ergogenic aid. The standard dosing protocol of 3-5g daily remains well-supported by the cumulative evidence base including this study.

For healthcare professionals: Understanding the specific mechanisms and safety data from studies like this helps clinicians provide evidence-based guidance to patients who ask about creatine supplementation. The research consistently shows a favourable safety profile at recommended doses.

For the Malaysian context: While most creatine research is conducted in Western populations, the fundamental biochemistry (ATP-phosphocreatine system) is universal. Malaysian consumers can apply these findings with confidence, adjusting for local factors like tropical climate (increased hydration needs) and halal dietary requirements (synthetic creatine monohydrate is permissible).

How This Fits Into the Broader Evidence

No single study should be used to make definitive claims about creatine supplementation. Instead, this research should be viewed as one piece of a much larger evidence base:

• The ISSN Position Stand (2017) synthesises hundreds of studies into comprehensive recommendations
• Multiple systematic reviews and meta-analyses confirm creatine’s effects on strength, power, and lean mass
• Long-term safety data spanning up to 5 years shows no adverse effects at recommended doses

For a complete overview of the evidence, explore our Research Library which covers 60+ landmark creatine studies.

Sources & References

This page summarizes Poortmans & Francaux (2000). Full citation: Poortmans JR, Francaux M. Long-term oral creatine supplementation does not impair renal function in healthy athletes. Medicine and Science in Sports and Exercise. 1999;31(8):1108-1110. doi:10.1097/00005768-199908000-00011

What This Means for You

For the average creatine user, this research supports the following practical recommendations:

1. Choose creatine monohydrate — it remains the most studied and effective form
2. Take 3-5g daily — consistent daily dosing is more important than timing
3. Take it with food — insulin response from meals enhances muscle uptake
4. Be patient — full saturation takes 3-4 weeks without loading
5. Combine with exercise — creatine works best when paired with resistance or high-intensity training

For more on practical dosing strategies, see our creatine dosage guide.

Further Reading

• creatine dosage guide
• creatine safety profile
• creatine monohydrate
• creatine for muscle building
• creatine for longevity
• creatine stacking guide