How Much Caffeine You Should Actually Have—and When
Figure out the right amount of caffeine to boost alertness without disrupting your sleep
Figure out the right amount of caffeine to boost alertness without disrupting your sleep
Caffeine can give us a boost, but too much can mess with our sleep and make us feel jittery. So how do we know what’s the right amount?
Generally, government and health groups recommend that healthy adults consume no more than400 milligrams of caffeine a day. That comes out to about four, 8-ounce cups of coffee, says Jennifer Temple, a professor of exercise and nutrition sciences at University at Buffalo School of Public Health and Health Professions.
(No, that 20-ounce Starbucks Venti doesn’t count as one cup of coffee.)
And believe it or not, we are doing pretty well on this target. The average American adult consumes about 200 milligrams of caffeine a day and in Europe, it is 270 milligrams, according to a 2017 review study.
But not everyone is optimising their caffeine intake to maximise how it can help them—by sharpening concentration for work or giving them a boost before a run—without hurting their sleep or overall health.
Here’s how to think strategically about getting the most out of your daily dose.
Caffeine can help you focus and keep you alert.
About 100 to 150 milligrams—or one to 1.5 cups of coffee—is a ballpark amount that will deliver a boost, says Astrid Nehlig, an emeritus research director at the French National Institute of Health and Medical Research, who has studied caffeine’s impact on brain activity, though it varies from person to person.
The effects generally kick in about five minutes after consumption and increase to become optimal for between roughly 15 and 120 minutes, Nehlig says.
Caffeine has been linked to physical benefits, too. People walked more on days they drank coffee than on days they didn’t, according to a 2023 study of 100 people in the New England Journal of Medicine. Participants took an average of 1,000 more steps on days when they drank caffeinated coffee than when they didn’t.
Other studies have suggested that caffeine can sometimes help us work out harder, such as when we have it before high-endurance exercise like long runs or swims, or sports that require a sustained effort, like soccer, Nehlig says.
The same boost hasn’t been found with shorter efforts, such as a sprint. Caffeine doesn’t act directly on muscles but rather reduces your rate of perceived exertion and the time it takes you to feel exhausted.
Caffeine’s main negative for your health is that it can disrupt your sleep.
The NEJM study that found that people walk more on days when they drink caffeine also found a downside. On days when study participants could drink as much caffeinated coffee as they wanted, they slept on average 30 minutes less than on days they didn’t drink any.
The impact on sleep varies greatly depending on how fast you metabolize caffeine, says Gregory Marcus, a cardiologist and professor of medicine at University of California, San Francisco and first author of the NEJM study.
On average, it takes about 4.5 hours for half of the caffeine consumed to pass through your system. However, genetic differences make some people metabolise it slowly or quickly, doctors and researchers say. The population is roughly split between fast and slow metabolisers.
The sleeping and walking study tested whether participants were slow or fast metabolisers of coffee. Those that were slow metabolisers slept nearly an hour less on the nights they drank caffeinated coffee, while the fast metabolisers didn’t experience any impact on sleep.
The best source of caffeine is unsweetened coffee or tea, says Dr. Frank Hu, professor of nutrition and epidemiology at Harvard T.H. Chan School of Public Health. These drinks have other beneficial ingredients, such as polyphenols, which have antioxidant effects which reduce inflammation.
The caffeine content in coffee and tea can vary, but soda can’t have more than 71 milligrams per 12 ounces, per Food and Drug Administration regulations.
Adults get most of their caffeine from coffee, but the market for energy drinks is growing. Pay extra attention to the caffeine in these drinks, because some contain very high levels.
Getting caffeine from soda or energy or sports drinks makes it more likely you are also getting a high dose of sugar and empty calories, says Hu.
Kids under 12 should avoid caffeine, while 12- to 18-year-olds should have no more than 100 milligrams a day, according to the American Academy of Pediatrics. Pregnant women are advised to have no more than 200 milligrams of caffeine a day.
People with chronic conditions like high blood pressure, diabetes or heart disease might want to be more cautious about their caffeine consumption, Hu adds. The NEJM study found that on the days when participants consumed caffeine, they had more abnormal heart rhythms in the lower chamber of the heart, which is associated with a greater risk of developing heart failure.
And people who get migraine headaches should try to drink no more than 100 milligrams of caffeine a day, the equivalent of a mug of coffee, says Dr. Amaal Starling, a headache specialist and neurologist at Mayo Clinic in Scottsdale, Ariz. She advises her patients who have daily or severe headaches not to drink any caffeinated beverages or switch to decaffeinated coffee.
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Randy Boyagoda’s new novel, “Lords of Serendipity,” delivers a biting satire of cheating, politics and dysfunction across modern universities.
Administrative cowardice. Rampant cheating. The soaking and scamming of undergrads and grad students. Performative wokeism. Intensifying competition for international tuition dollars from an expansive China.
These are either the latest dire headlines about American higher ed or the myriad subplots of “Lords of Serendipity,” an ambitious new novel by Randy Boyagoda. Unlike most campus fiction, its scope extends well beyond the cloister of the liberal arts classroom to whammy the entire university system, from its financial model to its function within a globalized economy. Along the way, it skewers its lightning-rod targets with a precision too sharp to be considered entirely fictional.
That its author is not only well-versed in satire, having written four other novels in the genre, but is also a professor of English at the University of Toronto and an experienced college administrator, further blurs the lines between comic fiction and brutal fact. It’s the kind of no-holds-barred book only a consummate insider would know to write—but only one who is also conveniently outside the American university system could get away with writing.
“This is someone who’s got the inside dope on what can go on at universities, especially with international students, and what kind of con games are going on,” said Margaret Atwood, a friend and fellow Torontonian.
The novel, like Boyagoda himself, is often very funny—even as the dilemmas its characters face read as tragedy. Its cast includes the bickering members of a Sri Lankan hotel cleaner’s family, insecure American freshmen, dead-end third-tier college professors and their highflying Ivy League counterparts and dispirited university functionaries. An old-fashioned Dickensian tale, it sweeps across continents and campuses, from a classic liberal-arts college to a stand-in for Harvard University to an urban technical school to the dilapidated buildings of a state-run university in Sri Lanka.
“I’m a joyful person,” Boyagoda said in an interview, though he prefers to see his outlook on academia as “hopeful” rather than optimistic. He smiles and laughs frequently. He bikes everywhere. He derives energy from his students and from his four daughters, ages 14 to 20. They help him and his American wife, Anna, also an educator, care for Boyagoda’s father, an immigrant from Sri Lanka who has dementia and lives with the family.
The germ of the novel came to Boyagoda during the pandemic, when he was serving as a vice-dean. An urban legend was circulating about a statistics grad student selling passing grades to international students. The cheating scheme itself may well have been apocryphal, but it felt tantalizingly plausible.
“As a novelist, it stayed with me,” Boyagoda said. “Who would sell grades for a stats course? Why would someone buy grades? What’s motivating them? Why wouldn’t the university be doing something about it?” What he didn’t want to do, he explained, was write “another novel about a creative writing professor and his drama with students.”
In addition to writing novels—the first of which was a finalist for Canada’s prestigious Giller Prize; he’s written eight books in total—Boyagoda teaches literature full-time. For his students next semester, kids raised in a purportedly “post-literature era,” he’s assigning three 700-page novels, he noted mischievously, books by George Eliot, Ralph Ellison and Kiran Desai.
On RateMyProfessors, students remark on Boyagoda’s heavy assignments, tough grading and distaste for cellphones, but also hail his “comedy.” When alerted to these reviews, Boyagoda laughed. “Guilty as charged,” he said.
“Randy’s one of those people in academia who is very well educated but doesn’t have an ounce of superiority about him,” said John Irving, who frequently guest lectures in Boyagoda’s classroom. “It’s amazing to see how willing students are to talk in his classrooms, how little afraid they feel of being mocked or put down—he gets complete candor out of them.”
Negotiating competing interests seems to come naturally to him. Like many college campuses, after the Oct. 7 Hamas attack on Israel, the University of Toronto was embroiled in protests, encampments and discord; part of the school’s response was to convene a working group on civil discourse. Boyagoda was put in charge, serving for two years. It’s the kind of thankless task many professors would flee from, but Boyagoda relished the prospect and thinks the group, which is ongoing, made progress.
He has since pivoted to another formidable academic concern: the waning prestige of the humanities. In July, Boyagoda became the director of the Jackman Humanities Institute and special advisor on the humanities to the dean of arts and science. This fall, he is starting a series of gatherings he calls the Dead Book Club. (Dead writers feature heavily among his favorites: St. Augustine, Dante, William Faulkner, Evelyn Waugh, Saul Bellow.)
“The goal is to encourage students to read for its own sake and have conversation for its own sake,” Boyagoda said. “The importance of the humanities will be revealed to those who participate.”
“Lords of Serendipity,” which publishes next week, reflects Boyagoda’s commitment to the pursuit of knowledge: “I’m supposed to say I learn more from my students than they do from me, but no,” Boyagoda said. “I enjoy sharing my excitement and joy about literature and ideas. There are these moments when you are teaching and you can see someone’s face change because they didn’t know something and then they did. That moment when you’re actually watch someone enlarge themselves is deeply satisfying.”
In literary circles, Boyagoda is often referred to as a Catholic novelist, a description he embraces. “A novelist willing to give shape and voice to contemporary religious experience is needed,” Boyagoda said. “I understand myself as a Catholic novelist, provided that I’m not only a Catholic novelist, I’m also a South Asian novelist and I’m a Canadian novelist. I don’t want to be captive to one label.”
His characters, he said, are subjected to what he calls “Graham Greene character situations.”
“They are trying to do good in a fallen world and realize the most they can do is less harm than someone else would do in that same role,” he explained. “They have to accept they are complicit in something that provides some good thing to others. It’s a very Graham Greene way of thinking about sacrifice.”
The campus green they inhabit is a febrile zone in which lofty ideals and cynicism regularly collide. It’s a place where a traditional holiday college celebration is now an occasion for political protest. Kids freely police one another inside and out of the classroom with social media their constant, ready weapon of choice. International students, knowing their family’s financial futures hinge on their degrees, operate in terror of failure and deportation.
Early readers of the book include Gary Shteyngart and Junot Diaz, both of whom have taught at universities and written comic novels. They each contacted Boyagoda midway through to say, in essence, “You nailed it.”
As biting as “Lords of Serendipity” can be, Boyagoda’s faith in higher education remains undaunted.
“It’s absurd that we live in societies that make the decision to take people between the ages of 18 and 22, when they are most physically capable of contributing to our nations and communities, and tell them, ‘Go away for four years, and read and learn and have conversations,’” he said. “I want students to be aware of what an incredible privilege that is.”
Corrections & Amplifications
Randy Boyagoda is a special advisor on the humanities to the dean of arts and science at the University of Toronto. An earlier version of this article incorrectly said he is a special adviser to the dean of humanities. (Corrected on Sept. 2)