Why is urine yellow?

You've probably wondered why your urine is yellow… Here’s why!

It has been known for almost a century that 𝐮𝐫𝐨𝐛𝐢𝐥𝐢𝐧 is responsible for the yellow color of urine but the enzyme by which this molecule is produced was still a mystery, until recently. Even though previous data showed that this enzyme was produced in the 𝐢𝐧𝐭𝐞𝐬𝐭𝐢𝐧𝐚𝐥 𝐦𝐢𝐜𝐫𝐨𝐛𝐢𝐨𝐭𝐚, in particular by the 𝐅𝐢𝐫𝐦𝐢𝐜𝐮𝐭𝐞𝐬 𝐬𝐩𝐞𝐜𝐢𝐞𝐬, this specific enzyme had never been precisely identified.

In an article published in 𝑁𝑎𝑡𝑢𝑟𝑒 𝑀𝑖𝑐𝑟𝑜𝑏𝑖𝑜𝑙𝑜𝑔𝑦, researchers have revealed that this molecule is produced by the 𝐜𝐨𝐧𝐯𝐞𝐫𝐬𝐢𝐨𝐧 𝐨𝐟 𝐛𝐢𝐥𝐢𝐫𝐮𝐛𝐢𝐧 𝐛𝐲 𝐭𝐡𝐞 𝐛𝐢𝐥𝐢𝐫𝐮𝐛𝐢𝐧 𝐫𝐞𝐝𝐮𝐜𝐭𝐚𝐬𝐞 𝐢𝐧𝐭𝐨 𝐮𝐫𝐨𝐛𝐢𝐥𝐢𝐧. Bilirubin is a molecule produced during the degradation of 𝐫𝐞𝐝 𝐛𝐥𝐨𝐨𝐝 𝐜𝐞𝐥𝐥𝐬, the breakdown of which takes place in the intestines. It is important that bilirubin does not stay long enough to be reabsorbed by the intestines, as too much bilirubin in the blood 𝐜𝐚𝐧 𝐜𝐚𝐮𝐬𝐞 𝐣𝐚𝐮𝐧𝐝𝐢𝐜𝐞, particularly in infants.

The appearance of jaundice at this age may be linked to the fact that bilirubin reductase production is 𝐨𝐧𝐥𝐲 𝐩𝐫𝐞𝐬𝐞𝐧𝐭 𝐢𝐧 𝐚 𝐭𝐡𝐢𝐫𝐝 𝐨𝐟 𝐧𝐞𝐰𝐛𝐨𝐫𝐧𝐬 during the first month of life, with a gradual increase over the first few months. This absence of bilirubin reductase has also been observed in patients with 𝐢𝐧𝐟𝐥𝐚𝐦𝐦𝐚𝐭𝐨𝐫𝐲 𝐛𝐨𝐰𝐞𝐥 𝐝𝐢𝐬𝐞𝐚𝐬𝐞.