Originally published at: Mystery solved: science reveals why urine is yellow - Boing Boing
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“This discovery lays the foundation for understanding the gut-liver axis.”
Tonight my Whiskey-Beer-BBQ Allies will be taking on the Gut-Liver Axis!
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Huh, interesting. I have Gilbert’s Syndrome which means my Billirubin is a bit high.
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Why? Because you don’t want to eat that snow.
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“It’s remarkable that an everyday biological phenomenon went unexplained for so long, and our team is excited to be able to explain it.”
Did it never occur to this research team that no-one else was looking for the answer? 
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So it’s not riboflavin?
“As a water-soluble vitamin, any riboflavin consumed in excess of nutritional requirements is not stored; it is either not absorbed or is absorbed and quickly excreted in urine, causing the urine to have a bright yellow tint.”
If one’s urine is darkly colored (yellow or otherwise), try better hydration! 
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“Oh, and I’ll give you a little tip: urine should only be green if you’re Mr. Spock.”
– Arnold J. Rimmer BSC, SSC
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but shouldnt it -I dont know- be blue? cause mr spock has green blood, humans red blood and yellow…piss. and red…piss…would be…well, you know…
The idea was Vulcan blood is green because of the copper it contains, just as our blood is bright red from the iron it contains. Bile pigments are forms excreted without any of the metal, and tend to be green (like in duck poop) to yellow or brown (like in our poop) depending on oxidation.
Of course no reason an alien wouldn’t have other waste products entirely, but blue is a less common color for organic pigments in general. So I wouldn’t assume it and definitely not from their blood.
@stevev, you find riboflavin all through the living world, but not usually enough for it to contribute much to visible color. You can get enough vitamin A to tint your skin too but you probably shouldn’t.
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I suspect this is not the groundbreaking discovery it is presented as, liver function (in adults) and in combination with inhibitors in breast milk, in infants, play a much larger role in jaundice than microbial enzymes. Interesting, though.
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so. perfect. thanks 
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A friend of mine had meningitis, and one of the drugs he was given to treat it turned all his bodily secretions bright orange. Even his tears.
(He recovered fine)
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But here on earth, copper-based blood (found in horseshoe crabs, molluscs, and some arthropods) is blue when oxygenated, and colorless when not.
I’m guessing the association of copper with the color green came from verdigris on copper and bronze.
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But you still want to be able to write your name.
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A little confusing to say “the yellow color comes from a microbial enzyme called bilirubin reductase” when bilirubin reductase isn’t present in urine. It’s long been known that the molecule urobilin gives urine its yellow color, so this discovery is about the pathway of how that molecule is produced during the breakdown of bilirubin. It is quite interesting that a gut microbe enzyme is responsible.
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Yeah, guess she found a better sample… 
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