Science answers, "Why is pee yellow?"

Scientists have finally determined what makes your pee yellow!

The discovery of bilirubin reductase, a by-product of some bacteria responsible for gut health, is the answer to the age old question "why is my pee yellow?" Having discovered this, the scientists from the University of Maryland also believe the enzyme plays a role in all sorts of things, from obesity to heart disease.

The enzyme that has eluded us for so long is now known as bilirubin reductase. It was identified by researcher and assistant professor Brantley Hall of the University of Maryland, who was part of a team based at the university and the National Institutes of Health.

Bilirubin is an orange pigment released by red blood cells after they die. Gut microbes then use bilirubin reductase to break down bilirubin into colorless urobilinogen, which degrades into yellowish urobilin, giving urine that infamous hue. While urobilin previously had an association with the color of urine, the enzyme that starts the process by producing urobilinogen was unknown until now.

"Though it was previously thought that multiple enzymes were involved in the reduction of bilirubin, our results support the finding that a single enzyme performs the reduction of bilirubin to urobilinogen," the research team said in a study recently published in Nature Microbiology.