If you’ve ever had an afternoon cup of coffee that wound up keeping you up that night, you’re probably well aware that caffeine too close to bedtime is a no-no. But why does this actually happen, and how close to bedtime can you get away with sipping? Here’s a look at what the research tells us.
How caffeine affects sleep.
First off, it’s important to remember that everyone metabolizes caffeine differently, so not everyone is going to respond to it in the same way. But what we do know is that, no matter who you are, caffeine can elevate your levels of cortisol, aka the stress hormone.
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As sleep expert and holistic psychiatrist Ellen Vora, M.D., previously explained to mbg, caffeine has a half-life of five to seven hours for most people, meaning it takes roughly six hours for your body to metabolize half of that cortisol-inducing caffeine—and another six hours to metabolize half of that.
“A cup of coffee at 9 a.m. is still lingering in your body at bedtime, and having a cup of coffee at 3 p.m. is effectively like drinking half a cup of coffee at 9 p.m.,” she says, adding, “even a little bit of caffeine lingering in the body can disrupt the quality of your sleep.”
While new research shows that caffeine might not affect certain body functions (such as heart rate) as much as we previously thought, gastroenterologist Marvin Singh, M.D., previously told mbg that he still recommends drinking less of it if it makes you experience things like anxiousness, headaches, digestive issues, and of course, sleeplessness—no matter what time of day it is.
So how long before bed should you stop sipping?
So, when should you actually cut the caffeine if you want to ensure you can fall asleep? Again, this will depend on the person, but according to one study that looked into caffeine intake zero, three, and six hours before bed, you’ll want to stop sipping at least six hours prior to bedtime.
Still, the study authors write, “caffeine consumption even 6 hours before bedtime can have important disruptive effects on both objective and subjective measure of sleep” in some people, so the “at least” is important here.
With that being said, it’s also important to keep in mind that different beverages have different amounts of caffeine. While a small cup of green tea in the afternoon might not affect your sleep, two 16-ounce coffees in the afternoon probably will.
We all metabolize caffeine differently, so blanket recommendations won’t necessarily hold true for everyone. If caffeine consumption is affecting your sleep, your best bet is to keep it early in the day and limit the amount you drink, too.
Once you figure out your personal sweet spot for when to put the coffee down (and practice good sleep hygiene in other ways, like avoiding eating too close to bedtime and keeping your bedroom cool), you’ll be able to rest easy—literally. Plus, you may just find that when caffeine isn’t affecting your sleep, you don’t actually need it to keep you awake during the day.