Asparagus Pee? Why Only Some People Smell It

Some people can smell the characteristic odor that asparagus gives to their urine, while others cannot. Now, a study reveals more than 800 new reasons why this strange phenomenon happens.

Researchers analyzed the genes of about 6,900 people and found 871 new genetic variants linked with an inability to detect this odor.

Lorelei Mucci, an associate professor of epidemiology at Harvard T.H. Chan School of Public Health,and her colleaguescame up with the idea for the study at a 2010 scientific conference where their dinner included asparagus. Mucci and her colleagues from the U.S. discussed the weird phenomenon of asparagus pee smell.

"To our surprise, our Scandinavian colleagues and our colleagues from Ireland had no idea what we were talking about," she told Live Science. [The 7 Biggest Mysteries of the Human Body]

This experience inspired Mucci and her colleagues to investigate the topic. In their study, the researchers asked 2,500 men and about 4,400 women — all U.S. citizens of European descent — whether they ever smelled this odor.

In the results, 40 percent of study participants said they could smell the odor in their urine after eating asparagus, and 60 percent said they could not.

More women than men said that they could not smell the odor, the researchers found. Specifically, 58 percent of men and 61.5 percent of women were unable to smell the odor, the researchers said in the study, published today (Dec. 13) in the Christmas issue of the journal The BMJ. The journal's annual Christmas issue is dedicated to real medical research on less-serious topics.

The researchers' analysis of the participants' genes revealed the hundreds of variations in DNA that were linked to being unable to detect smell.

The study had certain limitations, the researchers noted. For example, the participants self-reported their ability to detect the odor in question, and the researchers did not measure this ability in an objective way. Moreover, all of the participants were of European descent, so it's not clear whether the genetic results would apply to other ethnicities, the researchers said. [Tip of the Tongue: The 7 (Other) Flavors Humans May Taste]

It is not clear either how these genes work to prevent some people from detecting the odor, the researchers said. More research is needed to examine this question, the scientists said.

Originally published on Live Science.