The Reason Pee is Yellow

Environmental & Science Education, STEM, Health, Medicine, Miscellaneous

Ed Hessler

At some time, no doubt you've wondered why urine is yellow. It's a matter of biochemistry as this essay in Healthline by Kaitlin Vogel and Fact Checked by Jennifer Chesak for January 4 2024 explains.

First I must take a step backward. That the compound urobilin causes urine to be yellow has been known for more than a century, it is the mechanism that changes it from red-orange bilirubin - a waste product from degraded red blood cells - that has been identified. Enzymes and chemical breakdowns do the color transformation.

You may wonder why this has taken so long. According to  Brantley Hall, a microbiologist who studies gut bacteria, the bacteria responsible prefer low-oxygen environments and the conditions in the lab make it difficult to grow and perform experiments on them. He explained this in a statement in the language of biochemistry.

“Gut microbes encode the enzyme bilirubin reductase that converts bilirubin into a colorless byproduct called urobilinogen. Urobilinogen then spontaneously degrades into a molecule called urobilin, which is responsible for the yellow color we are all familiar with.'”

Vogel discusses some of the openings into the study of human health  this finding may lead and next steps which include human studies. This is followed by three short sections: the importance of paying attention to urine color, the role of the gut microbiome in human health, and three takeaways. 

 

Bilirubin is an interesting compound as you will learn from this article in Wiki.

The original paper was published in Nature Microbiology (linked as are most of the scientists involved).