Scientists have uncovered some staggering news: Many people have never smelled asparagus pee—and never will. The experts, writing in the British Medical Journal, say more than half of participants in a large survey reported an inability to pick up the scent.
People have been remarking on the odor of asparagus pee for just about as long as we’ve been eating asparagus. A bemused Benjamin Franklin noted the “disagreeable odour” the vegetable produced in his urine. Marcel Proust waxed lyrical on the subject, writing that asparagus spears “…played…at transforming my humble chamber into a bower of aromatic perfume.”
The precise cause of that perfume remains to be seen. Scientists’ current best guess is a natural compound called asparagusic acid, which is found only in—you guessed it—asparagus. On its own the acid smells fine; it’s after being processed through your body and coming out the other side that it acquires its signature scent.
Or at least it does for some people. Previous studies have suggested that the ability to smell asparagus pee is not as universal as we once thought. To find out, researchers at the Harvard T.H. Chan School of Public Health pulled data from two long-term projects on American health: the Nurses’ Health Study and the Health Professionals Follow-Up Study. Both studies had, remarkably, asked respondents about their ability to smell their own asparagus pee. All 6909 of the respondents had also submitted samples of genetic material.
The results were kind of astonishing. A full 58 percent of men and 61.5 percent of women said they’d noticed no unusual aroma in their pee after eating asparagus. That’s well over half of everyone in the study. All of the survey respondents, including the ones who could detect the scent, were of European descent, which means these results can’t be considered representative of everyone everywhere.
The researchers then looked at the DNA of smellers and non-smellers to see if they could find any differences. They could. The 4161 people with this asparagus anosmia collectively had hundreds of genetic variants, all located in the region of the chromosome associated with our sense of smell.
"Outstanding questions on this topic remain," senior author and epidemiologist Lorelei Mucci said in a statement. "First and foremost perhaps is: Why such a delicious delicacy as asparagus results in such a pernicious odor, and what are the selective pressures driving genetic variations that lead to asparagus anosmia?"
Pernicious or no, the aroma is one that Mucci and her co-authors imply is an olfactory experience millions are missing out on. They note that “future replication studies are necessary” but suggest a future of “targeted therapies to help anosmic people discover what they are missing.”