Can't smell asparagus pee? Is Pokémon GO good exercise?

December 13, 2016

Boston, MA - A large proportion of individuals of European-American descent cannot smell "asparagus pee"--the unpleasant odor present in urine after people eat asparagus. And while Pokémon GO users step up their physical activity when they first start playing the game, that extra activity trails off after six weeks.

Those are the findings of two studies by Harvard T.H. Chan School of Public Health researchers that will be published in the December 17, 2016 Christmas edition of The BMJ. For more than three decades, the prestigious journal has devoted its Christmas-week issue to articles that are quirky, amusing, and creative -- but all scientifically sound.

'Pernicious odor'

To learn more about who can smell asparagus pee and who can't, Harvard Chan researchers surveyed 6,909 men and women of European-American descent participating in two long-term studies. They found that 58% of men and 62% of women were unable to smell the urinary metabolites produced after asparagus consumption. Those metabolites, the authors said, create "a rather malodorous bouquet."

The researchers linked this data with a genome-wide association study measuring nine million inherited genetic variants, called SNPs (single nucleotide polymorphisms), in the participants. They found that 871 of the genetic variations were associated with the inability to smell asparagus pee -- called, in technical terms, asparagus "anosmia." All of the SNPs were located in a chromosomal region that contains multiple genes having to do with the sense of smell.

The researchers said the discovery of these SNPs provides scientists with future research directions to uncover the genetic determinants of people's overall sense of smell.

Pointing out the potential health benefits of eating asparagus -- including a reduced risk of cancer, cognitive impairment, and cardiovascular-related diseases -- the researchers urged people to eat the stalky vegetable, even if they are among those able to smell the disagreeable odor afterwards.

"Outstanding questions on this topic remain," said senior author Lorelei Mucci, associate professor of epidemiology at Harvard Chan School. "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?"

Lead author was research associate Sarah Markt.

Funding for the study came from the National Cancer Institute at the National Institutes of Health (NIH) (UM1 CA167552, R01 HL35464, UM1 CA186107, R01 CA49449, R01 HL034594, R01 HL088521); National Cancer Institute at the NIH training grant (NIH T32 CA09001); and the Prostate Cancer Foundation.

"Sniffing out significant 'Pee-values': genome wide association study of asparagus anosmia," Sarah C. Markt, Elizabeth Nuttall, Constance Turman, Jennifer Sinnott, Eric B. Rimm, Ethan Ecsedy, Robert H. Unger, Katja Fall, Stephen Finn, Majken K. Jensen, Jennifer R. Rider, Peter Kraft, Lorelei A. Mucci, BMJ, online December 13, 2016, BMJ 2016;355:i6071, doi: 10.1136/bmj.i6071

Good workout? Not so much.

A second group of Harvard Chan researchers sought to determine if Pokémon GO users get more exercise than non-users. It's been suggested that the augmented reality game, which has been downloaded 500 million times worldwide since its launch in July 2016, may help promote and sustain greater physical activity because it encourages walking.

The researchers looked at physical activity among a group of 1,182 young adults using an iPhone 6 series smartphone, which automatically records numbers of steps taken while the device is being carried. They compared the average number of steps taken per day for each of the four weeks prior to installation of the game with the steps taken during each of the six weeks after installation among both users and non-users of the game.

Before the game was installed on their phones, those who played the game took, on average, 4,256 steps per day. Non-users took an average of 4,126 steps per day. In the first week after installation, Pokémon GO was linked with an average 955-step increase per day among players, while numbers of steps among non-players didn't change. But the additional steps among players gradually dropped off over the subsequent weeks -- and by the sixth week the increase was no longer significant.

The results suggest that the positive health impact of Pokémon GO is moderate and diminishes after six weeks of playing. Interventions aimed at increasing walking typically increase the number of steps by 2,500 daily, the researchers noted--more than the average Pokémon GO user added in their first week of playing. However, playing the game may have social benefits that go beyond just increased physical activity, they said. They also cautioned that Pokémon GO may carry risks--such as injuries and road traffic incidents that can occur when people walk and drive while looking at their phones to play the game.

"We are only at the beginning of understanding how augmented reality gaming can potentially be beneficial to health," said Katherine Howe, a Harvard Chan doctoral student and co-first author of the study. "They give people a reason to go outside, walk, and socialize. Imagine the potential of developing these games to not only increase physical activity but to also boost mental well-being, mood, cognitive abilities, and social interaction for patients, school-aged children, or seniors residing in nursing homes."

"Gotta catch'em all! Pokémon GO and physical activity among young adults: difference in differences study," Katherine B. Howe, Christian Suharlim, Peter Ueda, Daniel Howe, Ichiro Kawachi, Eric B. Rimm, BMJ, online December 13, 2016, BMJ 2016;355:i6270, doi: 10.1136/bmj.i6270
Visit the Harvard Chan School website for the latest news, press releases, and multimedia offerings.

Harvard T.H. Chan School of Public Health brings together dedicated experts from many disciplines to educate new generations of global health leaders and produce powerful ideas that improve the lives and health of people everywhere. As a community of leading scientists, educators, and students, we work together to take innovative ideas from the laboratory to people's lives -- not only making scientific breakthroughs, but also working to change individual behaviors, public policies, and health care practices. Each year, more than 400 faculty members at Harvard Chan School teach 1,000-plus full-time students from around the world and train thousands more through online and executive education courses. Founded in 1913 as the Harvard-MIT School of Health Officers, the School is recognized as America's oldest professional training program in public health.

Harvard T.H. Chan School of Public Health

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