Coffee is a nonnegotiable part of the day for many people. The smell alone can issue an almost Pavlovian response in humans, helping them feel more alert and energetic simply by being in the presence of its scent. And regular coffee drinkers make up more than half of the country’s population, with one survey finding that 64 percent of Americans aged 18 or over said they had at least one cup of coffee in the previous day. But as National Geographic recently reported, our DNA may tell us more about how we process caffeine (and subsequently, how coffee affects us) than we think.
For instance, ever wonder why for some people, coffee is an integral part of their day, while for others, the mere thought of the substance gives them jitters? Researchers believe the answer could be tied up in people’s DNA. “What we’re finding is that we have built-in genetic factors that help us with self-regulating our caffeine intake,” Marilyn Cornelis, a caffeine researcher at Northwestern University, told National Geographic. “It’s interesting how strong of an impact our genetics have on that.”
It’s no secret that regular coffee drinkers develop tolerance to caffeine over time, with studies as far back as 1968 documenting this phenomenon. And while some people swear by the stuff to get them through the day, there’s also a population of people who actively avoid it due to side effects like exacerbation of anxiety disorders and insomnia, as well as nausea and digestion problems. This, NatGeo explains, could be due to variations in DNA.
“For someone who has a genetic variant that leads to decreased caffeine metabolism, they’re more likely to consume less coffee compared to someone who has a genetic variant that leads to increased caffeine metabolism,” Cornelis told National Geographic.
When caffeine enters the human system, two genes are linked to much of the processing: CYP1A2 (which generates an enzyme in the liver that breaks down around 95 percent of consumed caffeine) and AHR (which regulates CYP1A2). How much caffeine flows in your bloodstream, and how long it circulates for, is determined by these two genes.
For someone like me, who can have a sip of coffee and feel anxious for the rest of the year, that might mean that I’m a slow caffeine metabolizer, meaning I create less of the liver enzyme linked to processing caffeine. Consequently, more caffeine may stick around in my body for longer, potentially having more lingering effects on me versus someone who is a quick metabolizer and can have several cups a day without thinking twice.
In unrelated research, biotech company 23andMe analyzed data from roughly 1.8 million users to investigate just how genetics might affect caffeine consumption, focusing on genetic variants near CYP1A2 and AHR to estimate how an individual’s body might handle caffeine. Based on data from customers across the country, 23andMe tells Bustle, as part of its efforts to source data for analysis on traits like caffeine consumption, people from North Dakota, Washington, Oregon, Utah, and Colorado were the states most likely to consume more caffeine than average based on their genes, based on their data. And despite New Yorkers’ penchant for slurping down coffee like it’s an IV drip, the data revealed that New York, alongside other East Coast states New Jersey, Connecticut, and Rhode Island (and outlier Hawaii) were the five states likely to consume less caffeine than average based on genetic predisposition.
Contrary to the sprawling lines of millennials at Starbucks, 23andMe’s data also indicated that people in their 20s were less likely to consume more caffeine than other age groups based on their genes, though women were more likely to consume more caffeine than men regardless of age. Baby boomers (people aged 55 to 70) were most likely to be genetically predisposed to more caffeine consumption than average. To clarify, though, just because someone isn't genetically predisposed to consume a lot of caffeine doesn't necessarily mean that they won't indulge in the habit anyway (and vice versa).
This is just the tip of the iceberg, of course. Other research has documented additional genetic variations that may contribute to how people respond to coffee, like the gene ABCG2. “Whether individuals with impaired ABCG2 function have higher or longer [central nervous system] exposure to caffeine and thus a lower caffeine dose requirement for neural effects merits further study,” one study, also authored by Cornelis, indicated.
Variations in the gene ADORA2A have also been linked to an individual’s response to caffeine; a 2008 study found that a 150 mg dose of caffeine had a significant association with caffeine-induced anxiety in individuals with a specific variant of that gene.
Though the body of research investigating the links between DNA and coffee tolerance is growing, more research is needed. For now, it's reassuring to know that I'm not alone in my java-intolerance, and that it may be linked to something as beyond my control as my genetics. But while I may not be as biologically predisposed to break down caffeine as someone else may be, you can pry my green tea out of my cold, dead hands.