People have spent centuries trying to prove caffeine is dangerous, but the science suggests otherwise

Life as Laboratory
Life as Laboratory

When Davis Cripe died in his South Carolina classroom last May, it was a shock to everyone who knew him. He was just 16, and healthy. His death made no sense, especially when the coroner said that he’d been killed by a substance most of us consume daily: caffeine.

It’s well-known that caffeine can, in extreme cases, be deadly. About 10 grams of the stuff will kill most people, making caffeine powder an easily accessible (albeit incredibly uncommon and likely painful) choice for suicide. But a typical cup of coffee has less than 100 milligrams—or just 0.1 grams—of caffeine. In other words, you’d need to drink 100 cups of coffee in rapid succession to hit the deadly dose.

For people without underlying medical conditions, it’s exceptionally hard to die from drinking caffeinated beverages because of how (relatively) little caffeine they contain. This is something King Gustav III of Sweden found out in the 18th century, when he conducted an experiment to see whether tea or coffee kills faster. Both test subjects lived well into old age, far outliving King Gustav and the researchers conducting the experiment.

Sweden’s King Gustav III, early caffeine skeptic. He probably should have been more skeptical of his own efforts to consolidate power, which led to his assassination in 1792.
Sweden’s King Gustav III, an early caffeine skeptic. (Alexander Roslin / Wikipedia)

The local coroner said his staff determined Cripe had died from a “caffeine-induced cardiac event causing a probable arrhythmia.” It wasn’t from downing a succession of caffeine pills; it was, the coroner said, because Cripe drank a combination of a large Mountain Dew, some unknown energy drink, and a cafe latte within a few hours.

There’s little scientific evidence suggesting that even high amounts of caffeinated beverages can cause heart arrhythmias. A 2016 study found that patients at high risk for arrhythmias could imbibe 500 mg of caffeine in a five-hour span without raising their risk of irregular heartbeat. And a meta-analysis of previous studies found no evidence outside of animal studies, where the animals were given exorbitantly high doses—on the order of 35 mg of caffeine per kilogram of body weight. That would be the equivalent of about 2,550 mg—or 25 cups of coffee—for a 160-pound (73 kg) adult.

Scientists and medical professionals concerned about caffeine generally focus on energy drinks, since they’re wildly popular but contain lots of ingredients that interact in unknown ways, or on combinations of caffeine and alcohol, which get people drunker even as they continue to feel sober. But while energy drinks may be a relatively new concoction, coffee and tea and other traditional caffeinated beverages are not. And there’s extensive research showing it’s wrong to suggest typical caffeine consumption is dangerous.

How caffeine affects the body

When you drink a caffeinated beverage, the chemical immediately dissolves and spreads through all the fluids in your body. The caffeine crosses into the brain within minutes, where it latches onto proteins that normally receive adenosine, a chemical that makes you drowsy.

Caffeine blocks receptors in the brain that would normally attach to adenosine, an enzyme that makes you drowsy.
Caffeine blocks receptors in the brain that would normally attach to adenosine, an enzyme that makes you drowsy. (David Elmenhorst / Journal of Nuclear Medicine)

Caffeine reaches its peak blood concentration between 45 and 60 minutes after you drink it. As time goes on, your liver degrades the caffeine in your blood, meaning there’s less and less to elbow out the adenosine molecules that make you tired. So before too long, you start to get sleepy again. In three to five hours, about half the caffeine from that cup of morning joe will have degraded, so it might feel like time for a refill.

In addition, your brain receptors for adenosine are linked with receptors for dopamine, the “feel-good” chemical. Coffee makes you chipper not just because it’s fighting off drowsiness, but also because it makes it easier for dopamine to do its job, which in turn increases your feelings of pleasure.

But dopamine is also the key ingredient to addiction; drugs like cocaine and amphetamine flood parts of the brain with it to hijack the brain’s reward system—the mental circuitry of motivation. After getting flooded with those feelings of pleasure, you’ll naturally seek those good feelings over and over again. Motivation is important to keeping you alive, like when your brain is making you eat. But it’s not so good when it’s making you snort just one more line at 4am when the bar is trying to close.

Caffeine addiction…or not

If you focus just on dopamine, caffeine looks sort of like really weak cocaine. It’s clear caffeine has reinforcing effects; drinking coffee makes you want to drink more coffee. What isn’t clear is whether it’s truly addictive.

“Caffeine-use disorder” is mentioned in the fifth and latest edition of the Diagnostic and Statistical Manual of Mental Disorders, the professional bible for identifying and categorizing mental health issues. But caffeine-use disorder isn’t a fully recognized diagnosis in the DSM-5; it’s a proposal, currently under consideration for further study.

The proposal for “Caffeine use disorder” in the DSM-5, where it’s included as a possible diagnosis that demands further study.
The proposal for “Caffeine use disorder” in the DSM-5, where it’s included as a possible diagnosis that demands further study. (DSM–5 / American Psychiatric Association)

It’s a contentious topic. If caffeine-use disorder became a recognized diagnosis, it would appear alongside opioid-use disorder, tobacco-use disorder, and other often-deadly addictions. This could “minimize the severity of other substance-use disorders,” says Maggie Sweeney, a psychiatry instructor at Johns Hopkins University. Others agree. “It really trivializes other known addictions, such as smoking—we know those are clear addictions,“ says Marilyn Cornelis, an assistant professor at Northwestern University. “If we were to ask someone to cut out smoking and they gave that up for a week, they might still crave it…. Coffee’s a little different. You can think about someone cutting back on their coffee, and they’ve been able to do it for a month. I don’t think they’re going to go crazy if they walk into a room with a bunch of coffee drinkers.”

Addiction is typically understood to be the result of exposure to a substance that increases dopamine in particular brain structures. Caffeine makes the brain more sensitive to dopamine, but it doesn’t actually increase levels of the chemical in the brain. In a 2002 study, scientists at the US National Institute on Drug Abuse gave caffeine to rats and then looked at the key brain structure involved in dependence. They found an increase in dopamine. But a team of European researchers could not replicate the results, and concluded in 2007 the American team had misplaced their caffeine tube in the test rats. Then in 2015, a US National Institutes of Health team undertook a similar experiment but on humans, and found no dopamine increase. For some scientists, this is clear evidence that caffeine is not addictive.

Astrid Nehlig, a research director at the French National Institute of Health and Medical Research, points out that addictions, by definition, negatively impact people’s lives, but caffeine generally does the opposite. “You get dependent on caffeine, but why do you like caffeine?” says Nehlig. “Because it wakes you up, it increases your well being, in addition to helping you be productive, etcetera. And it’s also very often drank in social conditions. You meet with people, you have a coffee. So it’s also part of a kind of ritual.”

The benefits of caffeine

Caffeine’s short-term benefits are obvious. But studies show coffee does far more than help you focus and improve your mood.

For example, lifelong coffee drinkers are less likely to have Alzheimer’s, Huntington’s, and Parkinson’s diseases. In addition, if you consume caffeine in the morning, it can help maintain circadian rhythms, keeping your body’s 24-hour internal clock consistent. When your circadian rhythms get out of whack, you’re at risk for all sorts of sleep disorders, as well as weight gain and mental health issues. (Of course, caffeine’s ability to affect your body’s internal clock is also why it might be bad to consume caffeine at night.)

In fact, some researchers suggest we should be drinking three or four cups of coffee a day, if we want to reap the full benefits of caffeine without losing sleep or feeling agitated. That said, everyone handles caffeine differently; for some people four cups in a day might keep them up all night. This, it turns out, is coded into your genetics.

In the past few years, researchers have identified specific variations in the human genome that enable certain people to metabolize caffeine faster. That explains why everyone’s experience with caffeine is different, and why any one-size-fits-all recommendation for caffeine is misguided. “For someone who can’t metabolize caffeine very quickly…one or two cups of coffee per day…might be equivalent to someone [else] drinking eight cups a day,” says Cornelis.

 Caffeine isn’t dangerous for most people, since we naturally stick to our limits In a 2016 study, researchers discovered that people who drink the most coffee are also the people whose bodies have the genetic code to break caffeine down faster. In other words, the study sample population was already doing a good job self-regulating their intake. This suggests caffeine isn’t dangerous for most people, since we naturally stick to our limits. So when you get jittery or have trouble sleeping, you’ll simply take that as a sign to drink a bit less in the future. And meanwhile, you’ll be getting the daily benefits of caffeine, and perhaps even building up your body’s defenses against neurodegenerative disease.

In addition, it’s very uncommon for people to have trouble cutting back on caffeine, if they do it gradually—say, foregoing that sixth cup of coffee, giving their body a week to re-equilibrate to five cups, then undergoing the same experience to get down to four cups a day and settling there.

The one caveat is that this research applies to the way most adults consume caffeine—namely, drinking coffee to fight drowsiness or withdrawal-like symptoms. Children often react very differently to the drug, likely due to a number of factors: their brains are still developing, they’re consuming different types of caffeinated beverages, and they’re drinking them for different reasons.

Caffeine’s effect on children

Until recently, not many scientists focused specifically on how caffeine affects children. A little over a decade ago, Jennifer Temple, now director of the State University of New York-Buffalo’s Nutrition and Health Research Laboratory, noticed how scant the research was on the topic, and started conducting caffeine studies on adolescents, She discovered that young people, ages 8-17, consume caffeine less consistently than adults, but more importantly (pdf), they consume it for entirely different reasons than adults.

“It’s less about combating fatigue and more about things like, ‘I use it to study for a test, or I use it to be better at playing video games, or I use it to feel high,’” Temple says. “They use a language that’s much more about performance-enhancement or mood-elevation, whereas in adults, the language…is much more centered on withdrawal reversal—‘so I wake up in the morning, I don’t want to get a headache, I don’t want to feel sluggish, I’ll drink my coffee.’” Temple says there’s no evidence that small-to-moderate doses of caffeine are dangerous for 8-17 year-olds, but she generally recommends children avoid caffeine entirely, because they don’t need it to be functional day-to-day, and it can interfere with their sleep.

 “It’s less about combating fatigue and more about… performance-enhancement or mood-elevation” 

Animal studies, though, suggest caffeine could harm children in ways that go beyond disrupting sleep. Scientists found rats that began consuming caffeine as adolescents develop more anxiety, and exhibit stress-hormone levels reminiscent of people with PTSD. They didn’t find the same effect for adult rats that consumed caffeine. In one study from 2014, scientists found that adolescent rats exposed to caffeine become more sensitive to cocaine, suggesting caffeine might be a risk factor for hard-drug abuse later in life.

“I wouldn’t go as far as say it’s a gateway drug,” says Casey O’Neill, the lead author of the 2014 study, and currently at the Medical University of South Carolina. “I don’t think there is such a thing as this gateway effect.” However, O’Neill adds, if caffeine consumption makes people more sensitive to cocaine, they may be more likely to enjoy their first bump. And that could increase their odds of getting addicted.

Rats aren’t perfect analogs for people. The rodents metabolize caffeine exceptionally fast, so researchers have to give them extremely high doses of caffeine to mimic levels typically consumed by humans. And without human studies, it’s impossible to fully substantiate claims that caffeine is actually harmful to children, or to confirm suspected health benefits. If you really wanted to determine whether caffeine is dangerous for children, you’d need to give kids consistent doses of the drug for months or years—which would be an ethical (and logistical) nightmare.

That leaves an information gap where tragedies like Davis Cripe’s death take on more meaning than they probably should. It remains unclear why exactly Cripe died. But even if caffeine did play a role in Cripe’s death, it was likely a one-in-a-billion case, or the result of an unidentified interaction between some of the many substances he consumed so quickly. For nearly everyone on the planet, the level of caffeine Cripe consumed would have been innocuous. In reality, it’s impossible to make general claims about the dangers of caffeine based on one boy’s death—particularly when, for so many people, caffeine appears to be beneficial.

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