Study identifies why some people can smell asparagus in urine

December 13, 2016, British Medical Journal
Credit: public domain

In The BMJ's Christmas edition this week, a study identifies the genetic origin of the ability to smell the strong, characteristic odor in human urine produced after eating asparagus.

A team of U.S. and European researchers found hundreds of variants in the DNA sequence across multiple genes involved in sense of smell that are strongly associated with the ability to detect asparagus metabolites in urine.

They say more research is needed to understand why such food results in a particular odor, and what selective pressures would result in such a significant genetic predisposition to be able to smell - or not smell - the metabolites.

Asparagus is considered a delicacy, but it's also known to produce a distinctive odor in urine. Not everyone can detect the odour of metabolites (methanethiol and S-methyl thioesters) produced by consumption of asparagus.

The researchers, led by Sarah Markt and Lorelei Mucci at the Harvard T.H. Chan School of Public Health, set out to determine whether genetic factors are important in the ability to smell the odor.

Their study involved 6,909 men and women of European-American descent from two cohorts: the Nurses' Health Study and Health Professionals Follow-up Study.

Findings show that 40% (2,748/6,909) of participants agreed that they could smell a distinct odor in their urine after eating asparagus, and 60% (4,161/6,909) said they could not and were labelled as 'asparagus anosmic'.

The researchers linked information from genome wide association studies on over 9 million genetic variants with the asparagus anosmia trait.

They discovered 871 particular variations in DNA sequence, known as single nucleotide polymorphisms, on chromosome 1 which were associated with being asparagus anosmic. These genetic variants were found in several different genes responsible for sense of smell.

They also found that a higher proportion of women reported they were unable to detect the odor, compared to men, despite women being known to more accurately and consistently identify smells.

The researchers suggest that this unexpected result might be due to under-reporting by a few modest women, or because they might be less likely to notice an unusual odor because of their position during urination.

Study limitations include self reporting of odor, rather than an objective measurement, although this is unlikely to explain their findings, and the sample focusing on people of European descent, so it's unknown whether the same genetic variants predict asparagus anosmia in other ethnicities.

The authors explain that "our findings present candidate genes of interest for future research on the structure and function of olfactory (sense of ) receptors and on the compounds responsible for the distinctive produced by asparagus metabolites."

"Future replication studies are necessary before considering targeted therapies to help anosmic people discover what they are missing."

They also note that asparagus provides a rich source of iron, fiber, zinc, folate, and vitamins A, E and C, and consumption is thought to reduce risk of cancer, cognitive impairment, and cardiovascular related diseases.

Therefore, they call for research to "consider using these identified to better understand how a lifetime of eating might protect people from developing chronic conditions."

Explore further: Eating asparagus may prevent a hangover, study finds

More information: Sniffing out significant "Pee values": genome wide association study of asparagus anosmia, The BMJ, www.bmj.com/content/355/bmj.i6071

Related Stories

Eating asparagus may prevent a hangover, study finds

January 3, 2013
Drinking to ring in the New Year may leave many suffering with the dreaded hangover. According to a 2009 study in the Journal of Food Science, published by the Institute of Food Technologists (IFT), the amino acids and minerals ...

Witnesses can catch criminals by smell

June 9, 2016
Move over sniffer dogs, people who witnessed a crime are able to identify criminals by their smell. Police lineups normally rely on sight, but nose-witnesses can be just as reliable as eye-witnesses, new research published ...

Recommended for you

Eating at night, sleeping by day swiftly alters key blood proteins

May 21, 2018
Staying awake all night and sleeping all day for just a few days can disrupt levels and time of day patterns of more than 100 proteins in the blood, including those that influence blood sugar, energy metabolism, and immune ...

Deep space radiation treatment reboots brain's immune system

May 21, 2018
Planning a trip to Mars? You'll want to remember your anti-radiation pills.

Receptor proteins that respond to nicotine may help fat cells burn energy

May 21, 2018
The same proteins that moderate nicotine dependence in the brain may be involved in regulating metabolism by acting directly on certain types of fat cells, new research from the University of Michigan Life Sciences Institute ...

Atomic-level study reveals why rare disorder causes sudden paralysis

May 21, 2018
A rare genetic disorder in which people are suddenly overcome with profound muscle weakness is caused by a hole in a membrane protein that allows sodium ions to leak across cell membranes, researchers at the University of ...

Hotter bodies fight infections and tumours better—researchers show how

May 21, 2018
The hotter our body temperature, the more our bodies speed up a key defence system that fights against tumours, wounds or infections, new research by a multidisciplinary team of mathematicians and biologists from the Universities ...

New era for blood transfusions through genome sequencing

May 18, 2018
Most people are familiar with A, B, AB and O blood types, but there are hundreds of additional blood group "antigens" on red blood cells—substances that can trigger the body's immune response—that differ from person to ...

4 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

gkam
1.6 / 5 (7) Dec 13, 2016
Since it was self-reported, maybe it was a failure to excrete the stuff rather than the inability to smell it.
rrrander
not rated yet Dec 14, 2016
I can detect coriander (raw) in the parts per ten thousand in food. I hate the stuff. To me, the taste contaminates anything it's in. Apparently being repelled by it is genetic.
xponen
not rated yet Dec 14, 2016
They didn't check the urine at all to confirm if the asparagus metabolite really exist in people who didn't smell it.
pntaylor
not rated yet Dec 14, 2016
"targeted therapies to help anosmic people discover what they are missing."

I can smell it and I can't imagine why someone would want the ability to smell it.
The only reason I can think someone would want You to smell it is because they can
and "misery loves company".
Believe me, the guy who can't smell it aint missin' nuthin'.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.