How Much Caffeine You Should Actually Have—and When
Figure out the right amount of caffeine to boost alertness without disrupting your sleep
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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At least for people who carry the APOE4 genetic variant, a juicy steak could keep the brain healthy.
3 min
Must even steak be politicised? The American Heart Association recently recommended eating more “plant-based” protein in a move to counter the Health and Human Services Department’s new guidelines calling for more red meat.
Few would argue that eating a Big Mac a day is good for you.
On the other hand, growing evidence, including a study last month in the Journal of the American Medical Association, suggests that eating more meat—particularly unprocessed red meat—can reduce the risk of Alzheimer’s in the quarter or so of people with a particular genetic predisposition.
The APOE4 gene variant is one of the biggest risk factors for Alzheimer’s.
You inherit one copy of the APOE gene from each parent. The most common variant is APOE3; the least is APOE2.
The latter carries a lower risk of Alzheimer’s, while the former is neutral. A quarter of people carry one copy of the APOE4 variant, and about 2% carry two.
APOE4 is more common among people with Northern European and African ancestry. In Europe the variant increases with latitude, and is present in as many as 27% of people in northern countries versus 4% in southern ones. God smiled on the Italians and Greeks.
For unknown reasons, the APOE4 variant increases the risk of Alzheimer’s far more for women than men.
Women’s risk multiplies roughly fourfold if they have one copy and tenfold if they have two. Men with a single copy show little if any higher risk, while those with two face four times the risk.
What makes APOE4 so pernicious? Scientists don’t know exactly, but the variant is also associated with higher cholesterol levels—even among thin people who eat healthily.
Scientists have found that cholesterol builds up in brain cells of APOE4 carriers, which can disrupt communications between neurons and generate amyloid plaque, an Alzheimer’s hallmark.
The Heart Association’s recommendation to eat less red meat may be sound advice for people with high cholesterol caused by indulgent diets.
But a diet high in red meat may be better for the brains of APOE4 carriers.
In the JAMA study, researchers at Sweden’s Karolinska Institute examined how diet, particularly meat consumption, affects dementia risk among seniors with the different APOE variants.
Higher consumption of meat, especially unprocessed red meat, was associated with significantly lower dementia risk for APOE4 carriers.
APOE4 carriers who consumed the most meat—the equivalent of 4.5 ounces a day—were no more likely to develop dementia than noncarriers. (
The study controlled for other variables that are known to affect Alzheimer’s risk including sex, age, physical activity, smoking, alcohol consumption and education.)
APOE4 carriers who ate the most unprocessed meat were at significantly lower risk of dying over the study’s 15-year period and had lower cholesterol than carriers who ate less. Go figure. Noncarriers, however, didn’tenjoy similar benefits from eating more red meat.
The study’s findings are consistent with two large U.K. studies.
One found that each additional 50 grams of red meat (equivalent to half a hamburger patty) that an APOE4 carrier consumed each day was associated with a 36% reduced risk of dementia.
The other found that older women who carried the APOE4 variant and consumed at least one serving a day of unprocessed red meat had a cognitive advantage over carriers who ate less than half a serving, and that this advantage was of roughly equal magnitude to the cognitive disadvantage observed among APOE4 carriers in general.
In all three studies, eating more red meat appeared to negate the increased genetic risk of APOE4.
Perhaps one reason men with the variant are at lower Alzheimer’s risk than women is that men eat more red meat.
These findings might cause chagrin to women who rag their husbands about ordering the rib-eye instead of the heart-healthy salmon.
But remember, the cognitive benefits of eating more red meat appear isolated to APOE4 carriers.
Nutrition is complicated, and categorical recommendations—other than perhaps to avoid nutritionally devoid foods—would best be avoided by governments and health bodies.
Readers can order an at-home test from any number of companies to screen for the APOE4 variant.
The Swedish researchers hypothesize that APOE4 carriers may be evolutionarily adapted to carnivorous diets, since the variant is believed to have emerged between one million and six million years ago during a “hypercarnivorous” period in human history.
The other two APOE variants originated more recently, during eras when humans ate more plants.
APOE4 carriers may absorb more nutrients from meat than plants, the researchers surmise. Vitamin B12—low levels have been associated with cognitive decline—isn’t naturally present in plant-based foods but is abundant in red meat.
Foods high in phytates (such as grains and beans) can interfere with absorption of zinc and iron (also high in red meat), which naturally declines with age. So maybe don’t chuck your steak yet.
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