Indoxyl sulfate is a uraemic toxin formed when gut bacteria metabolise the amino acid tryptophan into indole, which is then absorbed and converted into indoxyl sulfate in the liver. While small amounts are normally excreted via the kidneys, elevated levels may indicate impaired detoxification, dysbiosis, or renal stress. Indoxyl sulfate has been linked to oxidative stress, systemic inflammation, and vascular dysfunction—especially in individuals with compromised kidney function. It serves as a marker of both microbial activity and the body’s ability to process and eliminate metabolic waste.
It is a compound produced by bacterial breakdown of tryptophan in the gut. After absorption, it is processed in the liver and then eliminated by the kidneys.
High levels are regarded as harmful due to their pro-inflammatory and pro-oxidative effects, particularly on kidney and cardiovascular health.
Common causes include gut dysbiosis, protein-rich diets, impaired liver sulphation pathways, and reduced kidney clearance.
Supporting gut health with prebiotics and probiotics, reducing protein overload, and enhancing liver and kidney detoxification may help lower levels.