Benzoic acid and the body's own salicylic acid
What it found
In people, a labeled dose of benzoic acid was partly converted into a salicylic acid byproduct in urine.
Blood salicylic acid also stayed measurable in people and animals when dietary and gut bacterial sources were removed.
What they found
Studies in people
Fasting in people
In a person on a milk and water diet for 3 days, blood salicylic acid stayed above 0.1 micromoles per litre and urine salicylic acid plus salicyluric acid continued at around 2.1 micromoles per 24 hours.
After colon removal
Six patients who had their colon or rectum removed still had low levels of salicylic acid in their blood and continued to excrete salicylic acid plus salicyluric acid in urine for up to 5 days.
Labeled benzoic acid
After six volunteers took labeled benzoic acid, between 8 and 16 hours later a median of 33.9% of their urinary salicyluric acid carried the label. Labeled salicylic acid was also found, with a median of 3.4%.
Urine salicylate rise
In the two-person pilot, urine salicylic acid plus salicyluric acid rose from about 3.87 and 4.50 micromoles per 24 hours to 5.10 and 7.04 micromoles per 24 hours on the day after taking 1 or 2 grams of benzoic acid per day.
Animal and lab studies
Animal blood levels
Blood salicylic acid levels in carnivorous animals were similar to those in herbivores. Only the crustacean samples did not contain salicylic acid.
Germ-free animals
Germ-free rats had about 2.5 times more salicylic acid in their blood than control animals. Mice given neomycin also had slightly higher levels than untreated mice.
What the authors conclude
“The overall contribution of benzoic acid (and its salts) to the turnover of circulating SA thus requires further assessment.”
Also in their conclusions
- They conclude that salicylic acid is at least partially made inside the body and that benzoic acid can be converted into it in people.
- They suggest that salicylic acid should be reassessed as a possible bioregulator in animals, with a broad defensive role.
- They advise that the contribution of benzoic acid and its salts to circulating salicylic acid needs further assessment.
How it was done
The authors wanted to understand where salicylic acid in the body comes from, since vegetarians have levels that overlap with people taking low-dose aspirin, and diet explains less than 20% of the variation.
They measured salicylic acid in blood from many animals, including germ-free mice and rats. In people, they ran a 4-day diet study in two volunteers, a 3-day labeled study in six volunteers who took 1 g of 13C benzoic acid with each meal, and checked six surgical patients who had their colon removed.
What it can’t tell you
- The human studies were very small, so the results may not apply to everyone.
- The animal and germ-free results cannot show what happens in people.
- The study cannot show whether the small rises in salicylic acid from benzoic acid have any effect on health.
The paper
- Title
- Salicylic acid sans aspirin in animals and man: persistence in fasting and biosynthesis from benzoic acid
- Type
- Study
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Paterson JR, Baxter G, Dreyer JS, Halket JM, Flynn R, Lawrence JR (2008). Salicylic acid sans aspirin in animals and man: persistence in fasting and biosynthesis from benzoic acid. Journal of agricultural and food chemistry. doi:10.1021/jf800974zFree full textPubMed 19053387DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error