Ascorbic acid breakdown and oxalate formation in the body
What it found
In people, ascorbic acid breaks down into oxalate, and higher intakes can raise the amount of oxalate in urine.
The exact amount formed is still not known.
What they found
Studies in people
Daily breakdown and need
About 60 mg of ascorbic acid breaks down in the body each day. Women need 70 mg and men 90 mg from food to replace it and stay healthy.
Oxalate from breakdown
The breakdown of 60 mg of ascorbic acid could form up to 30 mg of oxalate per day. But the body normally makes only 10 to 25 mg of oxalate per day, so other pathways that do not make oxalate must exist.
Urine oxalate and intake
In people, taking 2 g of ascorbic acid increased urinary oxalate by 21.8% in normal subjects and 34.4% in stone formers. Another study found a 56% increase in normal subjects taking 1 g per day.
Stone risk in men
A study of about 50,000 male health professionals found that men taking more than 218 mg of ascorbic acid per day had a 31% higher risk of forming kidney stones than those taking less than 105 mg per day.
Stone risk in Sweden
In a large Swedish population, supplemental ascorbic acid intake was linked to a near 2-fold increase in stone risk.
Oxalate nephropathy cases
Case reports describe people who took large oral doses or received intravenous ascorbic acid and developed oxalate nephropathy, with calcium oxalate deposits in the kidney. Most needed dialysis, and two cases ended in death.
What the authors conclude
“Epidemiological evidence indicates that the amount of AA ingested is a risk factor for calcium oxalate stone disease and that this risk is associated with the amount of oxalate excreted in urine.”
Also in their conclusions
- They conclude that the amount of ascorbic acid ingested is a risk factor for calcium oxalate stone disease and that this risk is linked to the amount of oxalate excreted in urine.
- They state that it is not clear how much ascorbic acid is converted to oxalate, and that this knowledge is needed to find optimal intake levels for people with calcium oxalate stones.
- They advise that compromised kidney function combined with excessive ascorbic acid intake can lead to oxalate nephropathy in susceptible individuals.
How it was done
The authors wanted to understand how ascorbic acid is converted to oxalate in the body, because this could help explain the link between ascorbic acid intake and kidney stones.
They reviewed existing studies on ascorbic acid breakdown, including human trials, population studies, and laboratory work on the chemistry of ascorbic acid and its products.
What it can’t tell you
- The exact amount of oxalate formed from ascorbic acid in the body is still unknown because of limited human tissue studies and difficulty in measuring the breakdown products.
- The studies that followed people over time can show a link between ascorbic acid intake and stone risk, but they cannot prove that ascorbic acid causes stones.
- It is not known whether non-absorbed ascorbic acid can break down to oxalate in the gut.
Who paid
- Funding
- Funded by NIDDK NIH HHS (from the PubMed record).
- Conflicts
- Conflict of Interest: Authors declare no conflict of interest.
- Authors work at
- University of Alabama at Birmingham, USA
The paper
- Title
- Ascorbic acid intake and oxalate synthesis
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Knight J, Madduma-Liyanage K, Mobley JA, Assimos DG, Holmes RP (2016). Ascorbic acid intake and oxalate synthesis. Urolithiasis. doi:10.1007/s00240-016-0868-7Free full textPubMed 27002809DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error