- Caffeine can interfere with an important restorative sleep stage.
- This may happen even when you cut yourself off before 2 p.m., as often recommended.
- There are a few key signs caffeine is interfering with your sleep, according to doctors.
Anyone who loves their daily cup (or two, or three…) of coffee is probably very well acquainted with the caffeine “rules” out there to ensure it doesn’t mess with your sleep later on. Mainly, to stop drinking your coffee by early afternoon to give the caffeine enough time to leave your system. But what if an early cutoff isn’t enough to protect your sleep?
New research suggests that might be the case—at least for some folks.
The study, which was published in MDPI, analyzed data from 32 previous studies on sleep and caffeine use that included monitoring by electroencephalogram (EEG), which measures and records the electrical activity of your brain. The researchers discovered that people who used caffeine experienced sleep that was lighter and “more wake-like” compared to those who didn’t use caffeine, even when the participants got eight hours of sleep or more.
Those effects were especially strong during NREM sleep, the restful stage that makes up the bulk of your sleep time in which brain activity, breathing, and heart rate slow down.
The researchers were careful to note that everyone is affected differently by caffeine, and that some may find their sleep hindered even when they restrict their caffeine use to the morning. In fact, one of the studies they referenced found that when people took 200 milligrams (mg) of caffeine 10 minutes after waking up in the morning, they still experienced sleep changes on the EEG when they went to bed at their normal time.
Given that an estimated 75% of American adults drink coffee—and nearly half sip on the stuff daily—coupled with how many folks have sleep issues, it’s understandable to wonder about the link. There are a few things to consider if you’re concerned that caffeine—even early in the day—might be messing with your sleep, according to doctors.
Meet the experts: W. Christopher Winter, M.D., a sleep medicine physician and host of the Sleep Unplugged podcast; Aarti Grover, M.D., medical director of the Center for Sleep Medicine at Tufts Medical Center; Jamie Alan, Ph.D., an associate professor of pharmacology and toxicology at Michigan State University; Mitchell B. Gigandet, M.D., assistant professor of clinical neurology at Vanderbilt University Medical Center
How does caffeine affect sleep?
There are a few ways caffeine influences your brain—and thus your sleep. “It interferes with the normal signaling of adenosine, which accumulates in the brain during wakefulness and facilitates sleep,” says W. Christopher Winter, M.D., a sleep medicine physician and host of the Sleep Unplugged podcast.
As adenosine builds up, it increases your sleep pressure—that urge to fall asleep, explains Aarti Grover, M.D., medical director of the Center for Sleep Medicine at Tufts Medical Center. “Caffeine blocks the adenosine receptors in the brain, leading you to feel more alert and vigilant.”
Some people are able to sleep after they’ve had caffeine, but, as the study found, it can “degrade” the quality of sleep you have, Dr. Grover says. Specifically, it reduces NREM-stage 3 (N3) sleep, which is the deepest sleep we get during the night, she points out. “N3 sleep is responsible for us waking up feeling refreshed,” Dr. Grover says. It also plays a role in physical and immune recovery.
As a result, “you may not have gotten the most refreshing sleep that you could have,” says Mitchell B. Gigandet, M.D., assistant professor of clinical neurology at Vanderbilt University Medical Center—even if you technically slept a full eight hours.
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Here’s where things get even more complicated: Caffeine can interfere with your sleep, even when you follow the “rule” of cutting off your consumption after the morning hours. “Drinking a lot of caffeine, even during the beginning of the day, over time, can interrupt sleep because we are in a constant stimulated state and never really ‘come down’ from the effects of caffeine,” says Jamie Alan, Ph.D., an associate professor of pharmacology and toxicology at Michigan State University.
What do doctors suggest around coffee and sleep?
You’ve probably heard the advice to try to finish your coffee (or other forms of caffeine) before 2 p.m.—that overall recommendation hasn’t changed. However, the rate that caffeine dissipates in your body is highly variable based on your genes, any medications you’re on, what you eat, your metabolism, and more, Dr. Winter says. “It’s generally thought to be four to 10 hours, but more research like this lately has led to concerns that it sticks around longer,” he says.
As a result, you may think you’re doing great when you cut yourself off from caffeine by 2 p.m., but it could still be interfering with your sleep if you go to bed at 9 p.m.
Still, there’s a lot of variation here. “Some people are able to clear and metabolize caffeine faster than others; in these people, caffeine will have a shorter effect,” Dr. Gigandet says. “Others may not clear caffeine as readily, so there is a higher chance that more caffeine will be present in their body when they are trying to sleep.”
Dr. Grover also recommends looking at your bedtime and working your way backward when it comes to cutting yourself off from caffeine. “The recommendation is stopping all caffeine consumption at least eight to 10 hours before scheduled bedtime,” she says. So, if you plan to go to sleep at 10 p.m., give yourself a hard stop with caffeine by noon.
It can also be helpful to limit how much total caffeine you take in, making sure you have no more than 400 mg per day. One more hack, per Dr. Grover: Try to wait at least 90 minutes after you wake up to have coffee. This allows the natural cortisol awakening response in your body to kick in to help you feel more alert in the morning, so you may find you don’t need quite as much a jolt from your caffeine.
How to know if caffeine could be hurting your sleep
If you suspect that caffeine may be messing with your sleep, Dr. Winter suggests looking at sleep tracker data. Many smartwatches now offer this, and metrics like resting heart rate, periods of wakening, and heart rate variability, can be telling.
Dr. Grover also recommends paying close attention to how you feel in the morning. If you wake up feeling unrefreshed despite sleeping seven to eight hours, wake up several times in the night, and feel like you need coffee first thing to start your day, your caffeine use may be interfering with your sleep, she says.
“To test this, you could try moving your last caffeine intake one to two hours earlier every day to see if this improves your sleep onset and/or sleep quality,” Dr. Gigandet says. “If it does, then it is likely the caffeine was the cause.”
What Dr. Winter doesn’t recommend is assuming you’re good on the caffeine front if you cut yourself off by 2 p.m., regardless of how much coffee you have. “The ‘I can drink a pot of coffee and sleep great’ is not a great method,” he says.
But if you’ve tinkered with your coffee intake and timing and still feel like you’re not as well-rested as you should be, Dr. Grover recommends seeing a sleep medicine specialist to do a deeper dive into your health.
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