In the only randomised trial to test it directly, apple cider vinegar did not measurably change any of the urine markers linked to stone formation. In the same trial, coconut water and lemon water both raised urinary citrate — the thing that slows calcium crystals from growing. That trial enrolled twenty people, none of whom had ever formed a stone, so it settles less than it sounds.
What the trial did
The APUL trial, published in International Urology and Nephrology in 2026, was a randomised crossover study. Twenty participants were each assigned two of four drinks: apple cider vinegar, coconut water, lemon water, or diet orange soda. They drank one daily for a week, waited two weeks, then drank the other. Researchers collected 24-hour urine samples at baseline and after each week.
Twenty-four-hour urine is the standard way of measuring stone risk chemistry — citrate, calcium, oxalate, volume, pH — so the design measures the right things.
What it found
Apple cider vinegar produced no statistically significant change in any 24-hour urinary parameter.
Two other drinks did:
- Coconut water raised urinary citrate by about 274 mg per day (95% CI 68 to 480)
- Lemon water raised it by about 168 mg per day (95% CI 16 to 319)
Neither urine pH nor urine volume shifted significantly in any arm.
Citrate matters because it binds calcium in urine and slows crystal growth. Low urinary citrate is one of the more common findings on a stone-former's 24-hour collection.
The evidence that points the other way
If the story ended there it would be tidy, and it does not.
A 2019 study in EBioMedicine reported that among more than 9,000 people, those who consumed vinegar daily had higher urinary citrate and lower urinary calcium than those who did not. The same paper found that vinegar and acetate reduced calcium oxalate crystal formation in rats, and proposed a mechanism involving histone acetylation in kidney tubular cells. A 2022 paper reported a separate mechanism through gut bacteria.
So: observational data in thousands of people and animal experiments suggest a benefit. A small randomised trial in humans found none.
How to read that disagreement
Neither result cancels the other, and the honest position is that the question is open.
The APUL trial is the stronger design — randomisation is what separates cause from correlation — but it is very small, ran for one week per arm, and enrolled people who had never formed a stone. Someone with normal urine chemistry has less room to improve than someone with low citrate, which is a well-known reason small trials in healthy volunteers find nothing.
The 2019 data covers far more people, but observational studies cannot rule out that vinegar drinkers differ in other ways. A 2025 systematic review of dietary interventions in stone disease notes how few proper interventional studies exist in this area at all.
What would settle it is a larger randomised trial in people who actually form stones. That has not been done.
What none of this tells you
No study here measured whether anyone formed fewer stones. They measured urine chemistry, which is a proxy — a good one, and the one clinicians use, but not the outcome you care about.
If your own 24-hour collection shows low citrate, that is a specific finding with specific, well-studied management options, and it is a conversation to have with your clinician rather than a reason to reach for the vinegar bottle.
A note on the record
The PubMed entry for the APUL trial carries a DOI belonging to an unrelated 2007 paper in a different journal. We have cited it by PMID for that reason. Small thing, but if you go looking for the paper by DOI you will land somewhere else.