How Much Caffeine You Should Actually Have—and When
Figure out the right amount of caffeine to boost alertness without disrupting your sleep
By SUMATHI REDDY
Thu, Jan 11, 2024 10:49am
3 min
3 min
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.
Optimising the boost
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.
The downsides
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.
Where to get your caffeine
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.
Extra caution
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.
Copyright 2020, Dow Jones & Company, Inc. All Rights Reserved Worldwide. LEARN MORE
MOST POPULAR
Rugged coastal drives and fireside drams define a slow, indulgent journey through Scotland’s far north.
A haven for hedge-fund titans and Hollywood grandees, Greenwich is one of the world’s most expensive residential enclaves, where eye-watering prices meet unapologetic grandeur.
Their careers spanned the personal computing, internet and smartphone waves. But some older workers see AI’s arrival as the cue to exit.
By Lauren Weber & Ray A. Smith
Tue, Apr 7, 2026 4 min
4 min
Luke Michel has already lived through two technology overhauls in his career, first desktop publishing in the 1980s and online publishing later on. But AI? He’s had enough.
So when his employer, the Dana-Farber Cancer Institute, made an early-retirement offer to some staff last year, the 68-year-old content strategist decided to speed up his exit. Before, he had expected to work a couple more years.
“The time and energy you have to devote to learning a whole new vocabulary and a whole new skill set, it wasn’t worth it,” he said.
It isn’t that he’s shunning artificial intelligence—he is learning Spanish with the help of Anthropic’s Claude. But, at this point, he’s less than eager to endure all the ways the technology promises to upend work.
“I just want to use it for my own purposes and not someone else’s,” he said.
After rising for decades and then hovering around 40% in the 2010s, the share of Americans over 55 years old in the workforce has slipped to 37.2%, the lowest level in more than 20 years.
The financial cushion of rising home equity and stock-market returns is driving some of the decline, economists and retirement advisers say.
But for some older professionals, money is only part of the equation.
They say they don’t want to spend the last years of their career going through the tumult of AI adoption, which has brought new tools, new expectations and a lot of uncertainty.
Many people retire when key elements of their work lives are disrupted at once, said Robert Laura , co-founder of the Retirement Coaches Association and an expert on the psychology of retirement.
“Maybe their autonomy is being challenged or changed, their friends are leaving the workplace, or they disagree with the company’s direction,” he said.
“When two or three of these things show up, that’s when people start to opt out.”
“AI is a big one,” he adds. “It disrupts their autonomy, their professionalism.”
Michel, whose work required overseeing and strategizing on website content, has been here before.
When desktop publishing arrived in the 1980s, he was a graphic designer using triangles and rubber cement.
The internet’s arrival changed everything again. Both developments required new skills, and he was energized by the challenge of learning alongside colleagues and peers.
It felt different this time around. “Your battery doesn’t hold a charge as long as it used to,” he said.
He would rather spend his energy volunteering, making art, going to operas and chairing the Council on Aging in North Andover, Mass., where he lives.
In an AARP survey last summer of 5,000 people 50 and over, 25% of those who planned to retire sooner than expected counted work stress and burnout as factors.
About half of those retired said they had left work at least partly because they had the financial security to do so.
In general, older Americans are less likely than younger counterparts to use AI, research shows.
About 30% of people from ages 30 to 49 said they used ChatGPT on the job, nearly double the share of those 50 and older, according to a 2025 Pew Research Center survey of more than 5,000 adults.
Baby boomers and members of Generation X also experienced the sharpest declines in confidence using AI technology, according to a ManpowerGroup survey of more than 13,900 workers in 19 countries.
“We as employers aren’t doing a good enough job saying (to older workers), we value the skills that you already have, so much so that we want to invest in you to help you do your job better,” says Becky Frankiewicz , ManpowerGroup’s chief strategy officer.
Jennifer Kerns’s misgivings about AI contributed to her departure last month from GitHub, where the 60-year-old worked as a program manager.
Coming from a family of artists, she said, it offends her that AI models train on the creative work of people who aren’t compensated for their intellectual property. And she worries about AI’s effect on people’s critical-thinking skills.
So she was dismayed when GitHub, a Microsoft-owned hosting service for software projects, began investing heavily in AI products and expecting employees to incorporate AI into much of their work. In employee-engagement surveys, the company had begun asking them to rate their AI usage on a scale of 1 to 5.
When it came time to write reports and reviews, colleagues would suggest that she use ChatGPT.
“I’d be like, ‘I have no idea how to use that and I have no interest in using AI to write anything for me,’” she said.
It would have been more prudent to work until she was closer to Medicare eligibility, she said. But by waiting until her children were out of college and some of her stock grants had vested, the math worked.
Her first act as a nonworking person: a solo trip to Scotland, where she took a darning workshop and learned how to repair sweaters.
“The opposite of AI,” she said.
Employers already under pressure to cut workers—such as in the tech industry—may welcome some of these retirements, said Gad Levanon , chief economist at Burning Glass Institute, which studies labor-market data.
“The more people retire, the fewer they have to let go,” he said.
Some of the savviest tech users are also balking at sticking around for the AI upheaval. Terry Grimm, who worked in IT for 40 years, retired from his senior software consultant role at 65 last May.
His firm had just been acquired by a bigger firm, which meant learning and integrating the parent company’s AI and other tech tools into his work.
Until then, Grimm expected he might work a couple more years, though he felt that he probably had enough saved to retire.
“I just got to the point where I was spending 40 hours at work and then 20 hours training and studying,” said Grimm, who has since moved with his wife from the Dallas area to a housing development on a golf course in El Dorado, Ark.
“I’m like, ‘I’ll let the younger guys do this.’”
