Ugh, now coffee is bad for us too?
Like many of us, Emma Barnett starts her day with a cup of coffee.
“On a scale of one to 10 in terms of importance to my life, it’s at least an 11,” said Barnett, a communications professional who estimates she drinks “at least” three cups before noon and then an afternoon latte as a luxury. “It’s not as bad as when I used to work in restaurants and we’d all just drink Mother Parkers brewed coffee until you’d start to feel a hole in your stomach.”
Since Barnett works with people in different time zones, her day can start as early as 4 a.m.; when that happens, she might have five cups of coffee, sometimes six. According to new research from the University of Toronto, that might be enough to put some people at risk for kidney dysfunction.
Why are only some people at risk? Roughly half of us have a genetic variant that allows us to break caffeine down quickly (that’s good), whereas the other half eliminates the substance from our bodies slowly (not good). When it comes to coffee, the world appears to be divided into two types of people: fast metabolizers and slow metabolizers.
“Slow metabolizers are less able to get rid of caffeine efficiently from the body, so, it’s more likely to have adverse effects in the people who can’t get rid of it,” explained Ahmed El-Sohemy, a professor of nutritional sciences at the University of Toronto’s Temerty Faculty of Medicine.
“We made a discovery back in 2006 with a case control study, where we showed that coffee increases the risk of a heart attack, but only in those who have a particular version of a gene that makes them effectively slow metabolizers of caffeine,” he added.
El-Sohemy’s most recent research suggests slow metabolizers — who are also heavy coffee drinkers — might be at higher risk for kidney dysfunction, too. Unmanaged kidney dysfunction can lead to permanent damage to the vital organ that removes toxins from our blood.
What about tea? Or caffeinated soft drinks? The U of T researchers focused on coffee because, among their research subjects, it was the biggest contributor to dietary caffeine. Tea, if consumed in large quantities, could be a problem, but the average 16-ounce black tea has less than 100 mg of caffeine, whereas there is often over 300 mg in an extra-large coffee from a chain.
Even though I only drink one cup of espresso most days, I’m curious to know whether or not I have the “coffee gene.” I asked El-Sohemy if there was any way I could tell.
Short answer? Not easily. “Often, when I give a talk, someone will say, ‘Oh, I’m definitely a slow metabolizer because if I drink a cup of coffee in the afternoon it keeps me up at night,’ ” said El-Sohemy. “But there’s currently no link in terms of those types of physiological responses to caffeine and speed of metabolism.”
Whether it’s post-coffee anxiety, withdrawal headaches, or that magical ability some people have to drink coffee after dinner and still get a good night’s sleep, none of these reactions actually indicate whether or not you have the coffee gene, according to the team of researchers who have been working on the problem in the lab El-Sohemy runs. The only way to know is through genetic testing.
Many, if not all, of the currently available at-home nutrition-oriented DNA tests would include results for the coffee gene. They’re expensive, though — roughly $200 — and often take more than a month to process. Plus, the science that backs the recommendations given through DNA kits is still emerging, so it’s unclear if, aside from a definitive answer to the coffee gene question, the other results should be taken as gospel and directives for diet and lifestyle changes.
“I definitely don’t want to come across as trying to sell a genetic test,” said El-Sohemy. “So I’d advise people just assume they’re a slow metabolizer and limit intake to one cup per day.”
That would save money, for sure: both the cost of the test and money spent on that second cup of coffee every day. But is there really an appetite for cutting back on coffee? Our list of simple pleasures is getting shorter. Last month, the Canadian Centre on Substance Use and Addiction shared new guidelines on low-risk drinking that, essentially said there was no safe level of alcohol.
The friends that I polled blew off the idea of changing their coffee habits. One friend complained that they’re still trying to figure out whether to pay attention to the new “no safe level” of alcohol guidance. Another pointed out that, with microplastics in our blood, worrying about coffee was pretty far down the list.
“I drink one to two litres of coffee per day,” said Christina Veira, partowner of Bar Mordecai. “It is essential. It gives me joy. I wouldn’t stop drinking it unless the harm was truly and immediately devastating. I’ve reached the age where I’m willing to gamble with my mortality, mostly because the idea of living in the absence of pleasure sounds exhausting.”
Joan Arwen, a manager with the federal public service who likes her lattes, told me that if her doctor told her to stop she might pay attention. “But if it was just a report, I’d rationalize it away as a correlation not causality,” said Arwen. “Then I’d file it away with all the other conflicting and confirming reports over the years.”
The lead author of the paper, Sara Mahdavi, a former post-doctoral fellow in El-Sohemy’s lab, said that the use of genetic testing, although not necessarily refined enough for the home consumer, gives research like this an edge.
“Genetics becomes a very valuable tool that not only helps us identify who is most responsive or at risk but also helps reduce confounding factors,” she said, pointing out that, for example, added sugar and cream could be ruled out as influencing the results.
“The effects they observed were specifically due to the caffeine,” she added.
Despite this news, Barnett think she’s going to just gamble on being a fast metabolizer. It’s a 50-50 chance, right? Coffee is just too important to her life to give up. “The pandemic drove it home that coffee is just this really simple lovely luxury,” she said. “To paraphrase Ben Franklin, coffee is proof that God loves us and wants us to be happy.”