Study Overview
Poortmans and Francaux (1999) 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 (Poortmans & Francaux, 1999) .
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
Where This Fits in the Evidence
Poortmans and Francaux (1999) is one of the foundational data points behind the now-routine claim that creatine does not harm healthy kidneys. By following 175 athletes who had supplemented for as long as five years and finding GFR, plasma creatinine and urinalysis all within normal limits, it directly counters the long-standing myth that a benign, expected rise in creatinine signals renal damage. Its honest limits are that it is observational rather than randomised and confined to healthy people, so anyone with pre-existing kidney disease still belongs in a conversation with their doctor first. This study reads alongside the other long-term safety work gathered in our research library.
Sources & References
This page summarizes Poortmans & Francaux (1999).
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
If your kidneys are healthy, this is among the strongest reasons not to worry about long-term use: the athletes here supplemented for as long as five years with no decline in kidney function. The one practical step is to tell your doctor you take creatine before any blood test, so the expected, harmless rise in creatinine is not misread as kidney trouble. If you already have kidney disease, this study does not apply to you — clear it with your doctor first.