How Much Caffeine You Should Actually Have—and When
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How Much Caffeine You Should Actually Have—and When

Figure out the right amount of caffeine to boost alertness without disrupting your sleep

Thu, Jan 11, 2024 9:54amGrey Clock 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 than 400 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 metabolise 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.


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Our refrigerators, washing machines and ovens can do more than ever, from producing symmetrical ice cubes to remotely preheating on your commute home. The downside to all these snazzy features is that the appliances are more prone to breaking.

Appliance technicians and others in the industry say there has been an increase in items in need of repair. Yelp users, for example, requested 58% more quotes from thousands of appliance repair businesses last month than they did in January 2022.

Those in the industry blame a push toward computerisation, an increase in the quantity of individual components and flimsier materials for undercutting reliability. They say even higher-end items aren’t as durable.

American households spent 43% more on home appliances in 2023 than they did in 2013, rising from an inflation-adjusted average of $390 to $558, according to Euromonitor International. Prices for the category declined 12% from the beginning of 2013 through the end of 2023, according to the Labor Department.

One reason for the discrepancy between spending and prices is a higher rate of replacement, say consumers, repair technicians and others. That’s left some people wishing they had held on to their clunky ’90s-era appliances and others bargaining with repair workers over intractable ice makers and dryers that run cold.

“We’re making things more complicated, they’re harder to fix and more expensive to fix,” says Aaron Gianni, the founder of do-it-yourself home-repair app Plunjr.

Horror stories

Sharon J. Swan spent nearly $7,000 on a Bosch gas range and smart refrigerator. She thought the appliances would last at least through whenever she decided to sell her Alexandria, Va., home and impress would-be buyers.

That was before the oven caught fire the first time she tried the broiler, leading to a 911 call and hasty return. The ice-maker in the refrigerator, meanwhile, is now broken for the third time in under two years. Bosch covered the first two fridge fixes, but she says she’s on her own for the latest repair, totalling $250, plus parts.

“I feel like I wasted my money,” says the 65-year-old consultant for trade associations.

A Bosch spokeswoman said in an emailed statement that the company has been responsive to Swan’s concerns and will continue to work with her to resolve ongoing issues. “Bosch appliances are designed and manufactured to meet the highest quality standards, and they are built to last,” she said.

Kevin and Kellene Dinino wish they had held on to their white dishwasher from the ’90s that was still working great.

The sleeker $800 GE stainless steel interior dishwasher they purchased sprang a hidden leak within three years, causing more than $35,000 worth of damage to their San Diego kitchen.

Home insurance covered the claim, which included replacing the hardwood down to the subfloor and all their bottom cabinetry, but kicked the Dininos off their policy. The family also went without access to their kitchen for months.

“This was a $60 pump that was broken. What the hell happened?” says Kevin, 45, who runs a financial public-relations firm.

A GE Appliances spokeswoman said the company takes appliance issues seriously and works quickly to resolve them with consumers.

Increased complexity

Peel back the plastic on a modern refrigerator or washing machine and you’ll see a smattering of sensors and switches that its 10-year-old counterpart lacks. These extra components help ensure the appliance is using only the energy and water it needs for the job at hand, technicians say. With more parts, however, more tends to go wrong more quickly, they say.

Mansoor Soomro, a professor at Teesside University, a technical college in Middlesbrough, England, says home appliances are breaking down more often. He says that manufacturers used to rely mostly on straightforward mechanical parts (think an on/off switch that triggers a single lever). In the past decade or so, they’ve transitioned to relying more on sophisticated electrical and computerised parts (say, a touch screen that displays a dozen different sensor-controlled wash options).

When a complicated machine fails, technicians say they have a much harder time figuring out what went wrong. Even if the technician does diagnose the problem, consumers are often left with repairs that exceed half the cost of replacement, rendering the machine totalled.

“In the majority of cases, I would say buying a new one makes more economic sense than repairing it,” says Soomro, who spent seven years working at Siemens , including in the home-appliances division.

These machines are also now more likely to be made with plastic and aluminium rather than steel, Soomro says. High-efficiency motors and compressors, too, are likely to be lighter-duty, since they’re tasked with drawing less energy .

A spokeswoman for the Association for Home Appliance Manufacturers says the industry has “enhanced the safety, energy efficiency, capacity and performance of appliances while adding features and maintaining affordability and durability for purchasers.” She says data last updated in 2019 shows that the average life of an appliance has “not substantially shifted over the past two decades.”

When simpler is better

Kathryn Ryan and Kevin Sullivan needed a new sensor to fix their recently purchased $1,566 GE Unitized Spacemaker washer-dryer. GE wasn’t able to fix the sensor for months, so the couple paid a local technician $300 to get the machine working.

The repairman also offered them a suggestion: Avoid the sensor option and stick to timed dries.

“You should be able to use whatever function you please on a brand new appliance, ideally,” says Sullivan, a 32-year-old musician in Burbank, Calif.

More features might seem glamorous, Frontdoor virtual appliance tech Jim Zaccone says, but fewer is usually better.

“Consumers are wising up to the failures that are happening and going, ‘Do I really need my oven to preheat while I’m at the grocery store?’” jokes Zaccone, who has been in the appliance-repair business for 21 years.

He just replaced his own dishwasher and says he bought one with “the least bells and whistles.” He also opted for a mass-market brand with cheap and readily available parts. Most surprisingly, he chose a bottom-of-the-line model.

“Spending a lot of money on something doesn’t guarantee you more reliability,” says Zaccone.


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