Caffeine Interferes with Circadian Rhythm


You know that sleep is important for you.

But you might not realize just how important it truly is.

Getting enough sleep—which generally means at least seven hours, though individual needs vary—is one of the best things you can do to improve your health.

Lack of sleep has been linked to everything from obesity to cancer.

I would say that sleep is at least as important to your health as exercise. And you know how important exercise is.

But right around 30% of adults get less than six hours of sleep a night. The numbers in children are even worse.

The CDC admits that sleep-deprivation is a major public health problem.

And a worrying new research study reveals that lack of proper rest isn’t even the worst problem we have when it comes to sleep.

In fact, one substance that 90% of us consume on a daily basis is wreaking havoc on our circadian rhythms. Not only is that contributing to our lack of sleep—but it has many of the same adverse effects.

Avoiding this substance and the problems that come with it can be easy, and for most of us, painless as well. I’ll explain more in a moment.

But first, why should you be concerned with your circadian rhythms anyway?

Unnatural sleep

Most of us have heard of circadian rhythms. It’s the internal clock that tells your body when to wake up, go to sleep, be alert, or be drowsy.

What a lot of folks don’t realize is that circadian clocks don’t just affect our brains. It’s not merely a timer to distribute appropriate hormones at the appropriate time of day.

No—each cell in your body has a circadian clock. Brain cells and liver cells. Fat cells and blood cells.

And when your circadian clock is out of sync, it can have all sorts of adverse effects. Just like sleep deprivation, it can cause obesity, cancer and a whole host of other problems.

Now the bad news. 90% of us ingest caffeine during the day. And a new study published in Science Translational Medicine found that caffeine consumption late in the day can reset your circadian clock.

We all know that caffeine late at night can keep us up. But it turns out this isn’t just because of its stimulant effect—it’s also a total reset of our circadian clock.

That’s a double-whammy.

How to avoid clock problems

The study only looked at caffeine consumption late in the day. We don’t yet know if an early morning cup of coffee will have the same effect.

Or, even if it does, if the risks involved will be nearly as deleterious. If you reset your circadian clock just when the alarm should be going off anyway, that may prove relatively harmless.

But caffeine after around 5 o’clock should be avoided at all costs.

Especially if you’ve already had some earlier in the day.

That’s because caffeine has a six-hour half life. Meaning you’ll still have 50% of the caffeine you drank six hours ago in your system, and still have 25% after 12 hours.

Which means, if you have a cup of coffee at 10 am and another at 4 pm, at 10 pm you’ll still have ¾ of a cup’s worth of caffeine in you.

And that’s if you only have a cup. Make it two at each sitting, and it’s like having an espresso at bedtime.

The simple solution: Avoid all caffeine later in the day.

Of course that means coffee. But lots of people drink iced tea with dinner. There’s plenty of caffeine in that.

Others have cola. The caffeine therein is another good reason to stay away.

And—I’m so sorry—but most chocolate contains caffeine as well.

Chocolate has a lot of theobromide—a substance very similar to caffeine. But cocoa beans contain caffeine as well.

For instance, a bar (around six ounces) of dark chocolate usually has around 70 mg of caffeine. For comparison, an eight ounce cup of coffee has around 95 mg.

Milk chocolate contains less—but it also has much more sugar.

Bottom line, you should avoid caffeine anytime late in the afternoon, and onwards. You can probably get away with a little bit now and again—like dark chocolate chips sprinkled in oatmeal as a dessert.

But don’t make a habit of it.

This is only one part of creating healthy sleep habits. For instance, exposure to bright light late in the day—such as you’d find on a computer monitor—is twice as damaging to your circadian clock.

But cutting late-day caffeine is still very important for sleep hygiene.

And, by extension, it’s very important for your health. Trust me—an increased cancer risk is never going to be worth that post-dinner coffee.


Last Updated: August 16, 2018
Originally Published: October 30, 2015