People who are highly sensitive to coffee’s bitterness drink more of it, researchers say. In other words, those who we would expect not to like coffee actually drink more of it than others. During our evolution, bitterness has been a warning sign to protect the body from toxic or harmful substances.
Therefore, by evolutionary logic, those more sensitive to caffeine’s bitter taste should reject it.
A team of Australian, American, and British researchers, however, found that the more sensitive individuals are to coffee’s bitterness, the more they drink it.
Marilyn Cornelis and colleagues wrote about their study and findings in the journal Scientific Reports (citation below). Cornelis is an Assistant Professor of Preventive Medicine (Nutrition) at Northwestern University Feinberg School of Medicine.
The authors say that a genetic variant causes the sensitivity.
Learned reinforcement elicited by caffeine’s bitterness
Prof. Cornelis said:
“You’d expect that people who are particularly sensitive to the bitter taste of caffeine would drink less coffee. 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.”
In other words, those who are highly-sensitive to coffee’s bitter taste learn to associate good things with the distinct bitter flavor of caffeine.
The people in this study population who were more sensitive to caffeine drank lots of coffee. However, they did not drink much tea. Cornelis suggested that perhaps they were too busy drinking coffee to consume tea.
The researchers also found that individuals who were sensitive to the bitter flavors of quinine and PROP avoided coffee. PROP (6-n-propylthiouracil) is a synthetic taste related to the compounds that exist in cruciferous vegetables. Brussels sprouts, cauliflower, cabbage, garden cress, bok choy, and broccoli, for example, are cruciferous vegetables.
People who were highly sensitive to the taste of PROP drank less alcohol, particularly red wine.
Prof. Cornelis said:
“The findings suggest our perception of bitter tastes, informed by our genetics, contributes to the preference for coffee, tea and, alcohol.”
Testing causal relationships
For this study, the researchers applied Mendelian randomization. This is a technique that scientists commonly use in disease epidemiology. They used the technique to test the causal relationship between bitterness (bitter taste) and beverage consumption. The study population consisted of over 400,000 men and women in the United Kingdom.
The genetic variants linked to quinine, PROP, and caffeine perception had been identified previously through genome-wide analysis of solution taste-ratings gathered from Australian twins.
The researchers then tested these genetic variants for associations with self-reported consumption of coffee in the current study. They also tested them with self-reported consumption of tea and alcohol.
Prof. Cornelis said:
“Taste has been studied for a long time, but we don’t know the full mechanics of it,” Cornelis said. “Taste is one of the senses. We want to understand it from a biological standpoint.”
Citation
“Understanding the role of bitter taste perception in coffee, tea and alcohol consumption through Mendelian randomization,” Jue-Sheng Ong, Daniel Liang-Dar Hwang, Victor W. Zhong, Jiyuan An, Puya Gharahkhani, Paul A. S. Breslin, Margaret J. Wright, Deborah A. Lawlor, John Whitfield, Stuart MacGregor, Nicholas G. Martin, and Marilyn C. Cornelis. Scientific Reports volume 8, Article number: 16414 (2018). DOI: https://doi.org/10.1038/s41598-018-34713-z.