Why some drink more coffee
Bitter tastes and genetics have surprising roles
Marilyn Cornelis has been thinking about coffee for most of her life. As a child, the Northwestern University Feinberg School of Medicine preventive medicine professor watched her father down cup after cup — “a couple of pots a day” and made a game of daring her siblings to lick the spoon he used to stir it. “It was so bitter to us,” she says.
That reaction to bitter tastes is universal, and it’s coded into our DNA — when humans needed to constantly seek food to sustain life, an aversion to bitter tastes kept people from jamming poisonous things into their mouths. Humans who hated bitter tastes lived to forage another day, which gave them the opportunity to spawn descendants, who are now standing in line at Starbucks.
Cornelis, whose academic research has focused on genetics and caffeine, is sometimes among them, she admits, though it takes some milk and sugar to get her to down the bitter brew. “I still can’t drink it black,” she says. Yet, in research published by Cornelis this month, she and colleagues at the QIMR Berghofer Medical Research Institute in Australia found that people who are genetically predisposed to be sensitive to the bitter taste of caffeine drink more coffee than those who are less sensitive or those who are sensitive to other bitter tastes such as quinine.
Cornelis says the finding was surprising. “Typically, humans avoid bitter tastes, and caffeine is one of those compounds, but people who were genetically sensitive to the taste of caffeine actually drank more coffee. So it might be that when you taste caffeine, you have learned to link that to stimulant effects.”
In other words, the desire for the stimulant effects of caffeine is so strong, we are willing to seek out a bitter taste to get it.
That stimulant-seeking behavior is controlled by different genetic variants — those that control the body’s ability to metabolize caffeine. If your genes are programmed to metabolize caffeine efficiently, you will burn through its stimulant effect more quickly, which is why you’ll spend more time at the office coffee pot than colleagues. “We are all sort of constantly titrating our own caffeine levels,” Cornelis says.
She and other researchers have identified about eight genetic variants that act on metabolism of caffeine and, as a result, predict consumption levels. But a genetic test for coffee junkies isn’t what researchers are after. Instead, studying caffeine and genetics may one day unlock some of the mysteries of caffeine’s protective effects on general health and diseases like diabetes and heart disease.
Large-scale studies have shown a link between lifespan and coffee consumption — people who drink around four cups per day live longer, and as scientists work to understand those effects, they may be able to harness that knowledge to combat disease.
The genetic link to bitter tastes has also been studied carefully. Scientists have shown that supertasters, who have more taste buds and actually taste everything more vividly than the rest of us, tend to avoid strong spices and have a stronger aversion to bitter. On the other hand, there are a few outliers who express a true like for bitter tastes (versus a learned tolerance). Correlations have been shown between this affinity for bitter tastes and “malevolent traits associated with a psychopathic personality, particularly the characteristic known as ‘everyday sadism,’ ” writes Brown University neuroscientist Rachel Herz.
Herz’s book “Why You Eat What You Eat” explores science and eating habits and points out that enjoyment of bitter tastes has implications for drinking and vulnerability to alcoholism. A study at Indiana University showed that beer drinkers experienced dopamine release that mimics the feeling of being intoxicated simply by tasting a bitter taste like beer.