The Study
Malic Acid Supplementation Increases Urinary Citrate Excretion and Urinary pH: Implications for the Potential Treatment of Calcium Oxalate Stone Disease
This study watched what happened to 8 healthy people’s pee after they took a supplement for a week. It saw some changes, but it didn’t compare them to people who didn’t take it. So we can’t say the supplement caused the changes — it might’ve been something else.
Analysis score
Maximum 44 for a cross-sectional study.
Where the score came from
Scientists gave people a daily dose of malic acid (found in apples) to see if it helps prevent kidney stones by changing urine chemistry.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 530 / 100
Quality score
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1The changes might help reduce some stones but could make others more likely — so it's unclear if it's a net benefit.
- 2After 7 days, urine became less acidic and had more citrate, but calcium and oxalate levels didn't drop enough to be sure it helped.
- 3Phosphate stone risk went up.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Journal of Endourology
Year
2014
Authors
A. Rodgers, D. Webber, Rachelle de Charmoy, G. Jackson, N. Ravenscroft
Related Content
Claims (6)
Malic acid at normal levels in the body does not lower calcium oxalate supersaturation by binding calcium; if calcium oxalate supersaturation decreases, it is due to another mechanism involving citrate.
Taking 1200 mg of malic acid daily for 7 days increases urinary pH and citrate levels in healthy adults, which is linked to lower calcium oxalate supersaturation, but does not significantly lower ionized calcium or calcium oxalate supersaturation.
Taking 1200 mg of malic acid daily for 7 days increases the levels of hydroxyapatite and tricalcium phosphate in urine and raises urinary pH, which changes the type of kidney stones a person is more likely to form from calcium oxalate to calcium phosphate.
Taking 1200 mg of malic acid daily for 7 days in healthy adults does not lower ionized calcium or calcium oxalate supersaturation, even though urinary citrate and pH increase, so the overall impact on kidney stone risk is not clearly reduced or increased.
Taking malic acid raises urine pH but does not change the tendency of brushite or octacalcium phosphate to form crystals, meaning that higher pH does not universally increase stone risk—it depends on the specific mineral compound.
Consuming citric acid and malic acid through food increases the amount of acid in the bloodstream and lowers the pH of the body's internal environment.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.