Scientists solve the age-old mystery of why urine is yellow

Scientists have discovered the real reason our urine comes out as a yellow colour.

For at least 150 years the topic of why our wee comes out a certain colour regardless of what we drink has been discussed.

And now, the mystery has finally been solved by researchers based in America. Scientists dedicated themselves to the toilet to solve the age-old question and reported their findings in a study in the journal Nature Microbiology.

Researchers from the University of Maryland and the National Institute of Health in the US combined for the study and said the reason our urine is the colour it is, is down to the enzyme bilirubin (BilR), which is created inside the body.

Urine constitutes of a mix of water, electrolytes and waste filtered out by the kidneys.

And researchers had previously worked out that the reason for the yellow tinge in urine came from a substance named "urobilin" back in 1868 but why it was yellow remained a mystery until now.

Bilirubin is a yellowish pigment made during the breakdown of red blood cells. Bilirubin passes through the liver and is eventually excreted out of the body. Normally it is tested to shed light on the possibility of liver or bile duct problems.

But scientists have worked out that it also has a key role in pigmenting the colour of a person's wee.

One of the research team, Brantley Hall, an assistant professor in the University of Maryland’s Department of Cell Biology and Molecular Genetics, said: "It’s remarkable that an everyday biological phenomenon went unexplained for so long, and our team is excited to be able to explain it."

He went on to say that the process "occurs when red blood cells reach the end of their life cycle at six months and degrade into the bright orange pigment bilirubin".

He added: "Typically, the pigment begins seeping into the gut, where it may either be excreted or partially reabsorbed. Upon reaching the gut, microorganisms in the intestines can transform bilirubin into various other molecules. Gut microbes encode the enzyme bilirubin reductase that converts bilirubin into a colourless byproduct called urobilinogen. Urobilinogen then spontaneously degrades into a molecule called urobilin, which is responsible for the yellow color we are all familiar with.

“We’re definitely standing on the shoulders of giants. If some of these older scientists had the technology we had today, they probably would’ve found it."

Dr Hall, who was the study’s lead author, said the medical breakthroughs could be used to help people combat things like inflammatory bowel disease and jaundice.

He said: "One of the major findings of our studies is that this gene was often absent in newborn babies. Now that we’ve identified this enzyme, we can start investigating how the bacteria in our gut impact circulating bilirubin levels and related health conditions like jaundice.

“This discovery lays the foundation for understanding the gut-liver axis.”