For tens of millions of people, a Monday morning without coffee is unthinkable. Keurig machines and cappuccinos are staples in offices and workplaces all over the world, and just the smell of a freshly brewed pot of coffee is enough to shake many from their bedsheets. On a purely scientific level, though, coffee really shouldn’t be all that popular. After all, its taste is objectively bitter, and bitterness has served as an evolutionary warning to the human body of harmful substances since mankind’s existence.
So, why then do so many people crave a cup of coffee in the morning? It turns out you may have never had a choice in the matter; some people are genetically predisposed to quickly develop a taste for some java.
An individual’s sensitivity to bitterness is linked to their genetics. In other words, some people are more sensitive to the bitter taste of coffee than others. Surprisingly, according to a study conducted at Northwestern University, it’s those individuals who actually end up visiting Starbucks more often.
“You’d expect that people who are particularly sensitive to the bitter taste of caffeine would drink less coffee,” comments senior author Marilyn Cornelis, assistant professor of preventive medicine at Northwestern University Feinberg School of Medicine, in a press release. “The opposite results of our study suggest coffee consumers acquire a taste or an ability to detect caffeine due to the learned positive reinforcement (i.e. stimulation) elicited by caffeine.”
Essentially, it’s that heightened bitter taste that allows many people to quickly develop “positive associations” with the taste of coffee. The more sensitive we are to coffee’s bitter taste, the faster our bodies pick up on the fact that drinking some coffee will result in some extra pep in our step.
These findings represent a rather humorous evolutionary role reversal. Our bodies developed varying levels of bitter sensitivity to protect us from poisonous foods hundreds of thousands of years ago. Today, that same sensitivity promotes coffee consumption and cravings.
It’s not just coffee either. Genetic differences in taste sensitivity probably influence our tea and alcohol preferences as well, the study’s authors say.
For instance, it was noted that within the studied population sample, participants who enjoyed the bitter taste of coffee and drank it frequently also largely stayed away from tea. Still, professor Cornelis speculates this observation may just be due to those people being too busy drinking coffee to make time for tea.
Of course, there are different types of bitterness, and some people are more sensitive to certain variations. Researchers found that individuals sensitive to the bitter flavors of quinine (found in tonic water) and PROP (similar in taste to kale, brussels sprouts) actually tended to avoid coffee. Moreover, individuals sensitive to the taste of PROP also drank less alcohol, especially red wine.
“The findings suggest our perception of bitter tastes, informed by our genetics, contributes to the preference for coffee, tea, and alcohol,” Cornelis adds.
Over 400,000 men and women from the United Kingdom were analyzed for this study, so it was hardly a small initiative in scope. Researchers used Mendelian randomization, a complex scientific technique usually used to track the onset and distribution of diseases, to assess the relationship between participants’ bitter sensitivity and subsequent coffee drinking habits. The specific genetic variants linked specifically to caffeine and coffee perception were originally discovered via extensive genome-wide analysis of Australian twins.
“Taste has been studied for a long time, but we don’t know the full mechanics of it,” Cornelis concludes. “Taste is one of the senses. We want to understand it from a biological standpoint.”
These findings are no doubt fascinating on a purely topical level, but besides their conversational potential, they are also a stark reminder of human adaptability. What acted as a survival helper thousands of years ago is still serving a purpose today, albeit one that may end up leading to some extra money spent on that second shot of espresso.
The full study can be found here, published in Scientific Reports.