Benzoic acid and salicylic acid production in animals and people
What it found
In six people, taking labeled benzoic acid led to about a third of a related substance in urine carrying that label.
Salicylic acid stayed in the blood during fasting in people and was found widely in animals.
What they found
Studies in people
Levels persist while fasting
One person on a milk and water diet free of salicylic acid kept steady blood levels for three days. Six patients fasting for major bowel surgery also kept salicylic acid in their blood for up to five days.
Benzoic acid becomes salicylate
Six volunteers took labeled benzoic acid with meals. Between 8 and 16 hours later, a median of 33.9% of a breakdown product in their urine carried the label, showing the body converted it.
Pilot dose increased excretion
Two people took 1 or 2 grams of benzoic acid daily for two days after eating a set menu. The amount of salicylates leaving in their urine rose, especially in the person taking the larger dose.
Animal and lab studies
Salicylic acid in animals
Blood samples from many species at a zoo contained salicylic acid. Carnivores had levels similar to plant eaters, and only crustaceans lacked it entirely.
Gut bacteria not the source
Mice given antibiotics to clear gut bacteria and germ-free rats actually had higher salicylic acid levels than normal animals. This suggests gut bacteria are not making it.
What the authors conclude
- They conclude that the human body can make salicylic acid from benzoic acid, meaning some of it comes from within rather than just from food.
- They suggest salicylic acid may act as a natural regulator in animals and people, much like it does in plants.
- They call for more work to measure how much benzoic acid and its salts add to the salicylic acid already circulating in the body.
How it was done
The authors knew salicylic acid appears naturally in people who do not take aspirin, but diet explained only a small part of it. They wanted to see if the body makes salicylic acid from benzoic acid, which is common in plants and used as a food preservative.
They measured salicylic acid in the blood of many animal species and in germ-free mice and rats. In people, they tracked levels during fasting for surgery and gave six volunteers labeled benzoic acid over three days to follow where it went.
What it can’t tell you
- This study followed only six people given labeled benzoic acid, so it cannot show how much this process matters in everyday life.
- The amounts of benzoic acid given were much larger than typical daily intakes, so results may differ at normal levels.
- Animal findings about gut bacteria and blood levels cannot directly prove what happens in people.
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 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error