Caffeine and Sleep: How Late Is Too Late?
If you are like millions of people, caffeine is part of your daily routine. Maybe you start your morning with coffee, have a cup of tea in the afternoon, or enjoy a cold Dr Pepper with lunch. Me? I drink 2.5 cups of coffee in the morning and as much Dr. Pepper throughout the day as I can get away with. I’m more cognizant of what I drink nowadays so my Dr. Pepper habit is shrinking.
There is nothing inherently wrong with caffeine. In fact, for most adults, moderate caffeine consumption is considered safe. The problem is that caffeine can stick around in your system much longer than you might think.
And when it comes to dementia prevention, sleep matters.
Getting enough good-quality sleep is an important part of taking care of your brain. Most adults, including older adults, should be getting about 7 to 9 hours of sleep each night. Poor sleep has been associated with problems with memory and thinking, and researchers continue to study the relationship between sleep and Alzheimer’s disease.
So, could that afternoon cup of coffee be interfering with your sleep?
How Much Caffeine Are You Actually Drinking?
Before we talk about when you should stop drinking caffeine, it helps to understand how much caffeine is actually in the drinks you consume.
The amount can vary considerably depending on the brand, brewing method, and serving size. But here are some useful numbers to give you a general idea:
| Beverage | Approximate Caffeine |
|---|---|
| 8 oz. brewed coffee | About 95 mg |
| 8 oz. black tea | About 47 mg |
| 8 oz. green tea | About 28 mg |
| 12 oz. Dr Pepper | About 41 mg |
| 12 oz. caffeinated soft drink | About 23-83 mg |
The FDA lists regular brewed coffee at roughly 113 to 247 mg per 12 ounces, depending on the coffee, while an 8-ounce cup of coffee is commonly around 95 mg. Black tea can contain around 47 mg per 8 ounces, although the actual amount varies.
A 12-ounce can of regular Dr Pepper contains about 41 mg of caffeine. That is considerably less than a typical cup of coffee, but it is certainly not caffeine-free.
That last point is worth remembering. A soda may not taste like coffee, but that doesn’t mean it doesn’t contain enough caffeine to affect your sleep.
And don’t forget that serving size matters. A large convenience-store coffee or a 20-ounce bottle of soda can contain substantially more caffeine than the numbers above.
Caffeine Doesn’t Disappear When You Stop Feeling It
Here’s where things get interesting.
Caffeine works by blocking adenosine, a chemical in your brain that builds up while you are awake and contributes to feelings of sleepiness. In other words, caffeine doesn’t necessarily give you more energy. It can temporarily prevent your brain from feeling as tired as it actually is.
The effects of caffeine can last for hours.
You might drink a cup of coffee at 3:00 PM and feel completely normal by bedtime. You may even fall asleep without any trouble.
That doesn’t necessarily mean the caffeine had no effect on your sleep.
One controlled sleep study looked at people who consumed 400 mg of caffeine at bedtime, three hours before bed, or six hours before bed. Even when the caffeine was consumed six hours before bedtime, researchers found significant disruption to sleep. Objective measurements showed that participants lost more than an hour of total sleep.
That’s a pretty big deal.
If you go to bed at 10:00 PM, that study suggests that a substantial dose of caffeine at 4:00 PM could still interfere with your sleep.
So When Should You Stop Drinking Caffeine?
There isn’t one perfect cutoff time that works for everyone.
People process caffeine differently. The FDA points out that caffeine sensitivity and the rate at which people eliminate caffeine from their bodies can vary considerably. Certain medications and medical conditions can also make someone more sensitive to caffeine.
But if you are trying to improve your sleep, six hours before bedtime is a good starting point for your caffeine cutoff.
For example:
Bedtime: 10:00 PM
Try to finish substantial caffeine by 4:00 PM
Bedtime: 9:00 PM
Try to finish substantial caffeine by 3:00 PM
Bedtime: 11:00 PM
Try to finish substantial caffeine by 5:00 PM
And if you have trouble sleeping, you may want to experiment with an even earlier cutoff.
Remember, this isn’t a magic rule. It is a starting point.
What About That Afternoon Dr Pepper?
This is where understanding caffeine quantities becomes useful.
Let’s say you normally drink a cup of coffee in the morning and a 12-ounce Dr Pepper at 4:00 PM.
Your morning coffee might contain around 95 mg of caffeine. The Dr Pepper adds another 41 mg.
The afternoon soda doesn’t seem like much compared with coffee, but it is still caffeine.
And if your goal is to improve your sleep, the question isn’t necessarily, “Is 41 mg of caffeine a lot?”
The better question is: “Do I need that caffeine six hours before I go to bed?”
If you go to bed at 10:00 PM, switching that 4:00 PM Dr Pepper to a caffeine-free beverage might be a simple experiment worth trying.
What About Tea?
Tea can be a little deceptive because people often think of it as a low-caffeine beverage.
It can be lower than coffee, but it isn’t necessarily low enough to ignore.
The FDA lists typical caffeine levels of about 71 mg for 12 ounces of black tea and 37 mg for 12 ounces of green tea.
So if you drink a large cup of black tea in the evening, you could be getting a meaningful dose of caffeine without realizing it.
Herbal teas are a different story. Many herbal teas, such as chamomile or peppermint, are naturally caffeine-free.
What About Decaf Coffee?
“Decaf” does not mean “zero caffeine.”
The FDA notes that an 8-ounce cup of decaffeinated coffee typically contains about 2 to 15 mg of caffeine.
That’s dramatically less than regular coffee, but it is still worth knowing if you are particularly sensitive to caffeine.
For most people, switching from regular coffee to decaf in the afternoon or evening could be an easy way to maintain the ritual of having a cup of coffee without getting nearly as much caffeine.
Don’t Forget the Other Sources
Coffee, tea, and soda aren’t the only places caffeine can hide.
Caffeine can also be found in:
- Energy drinks
- Chocolate
- Some protein or energy bars
- Certain dietary supplements
- Some over-the-counter medications
The FDA recommends paying attention to all of these sources when trying to control your caffeine intake.
And if you are consuming caffeine from several sources throughout the day, it can add up quickly.
The FDA says that up to 400 mg of caffeine per day is an amount not generally associated with negative effects for most adults. But that is not a recommendation that you should consume 400 mg every day, and it doesn’t mean that 400 mg won’t interfere with your sleep. Individual sensitivity varies.
Try a Simple Sleep Experiment
If you think caffeine might be affecting your sleep, don’t make this complicated.
Try this for one week:
Pick a caffeine cutoff time.
For example, if you normally go to bed at 10:00 PM, stop consuming caffeinated drinks after 4:00 PM.
Then pay attention to three things:
- How easily you fall asleep
- How often you wake up during the night
- How you feel the next morning
You don’t have to give up coffee.
You don’t have to give up soda.
You don’t even have to give up caffeine altogether.
You are simply testing whether when you consume caffeine makes a difference in how well you sleep.
If you notice an improvement, you have learned something useful about your own body.
Your Brain Needs Sleep
The goal here isn’t to convince you that caffeine is bad.
For most people, it isn’t.
The goal is to make you think about timing.
Sleep is one of the simplest things we can do for our overall health, yet many of us unknowingly make it harder by consuming caffeine too late in the day. Older adults generally need about 7 to 9 hours of sleep, and getting enough quality sleep supports memory, attention, mood, and overall health.
Researchers are also investigating the relationship between poor sleep and Alzheimer’s disease. Studies have found associations between inadequate or disrupted sleep and Alzheimer’s-related changes in the brain, although researchers are still working to understand exactly how the relationship works.
That’s why sleep belongs in any conversation about dementia prevention.
So enjoy your morning coffee.
Have your tea.
Drink your Dr Pepper.
Just consider moving your caffeine earlier in the day.
Your brain has a lot of work to do while you’re sleeping. Give it the best opportunity you can.
