Does Caffeine Really Mess with Your Sleep?

Introduction

“Caffeine doesn’t affect my sleep.” You’ve probably heard that one before—maybe even said it yourself while sipping a 4 p.m. cold brew.

And yet, for every person who swears they can drink espresso at dinner and sleep like a baby, there’s another who claims even a morning cup ruins their night. So who’s right?

A new systematic review from Australia set out to answer that question, analyzing 24 studies and 1,063 participants to see how caffeine dose and timing really influence sleep. The results? Eye-opening (pun intended).

What the Science Says

Caffeine’s half-life—the time it takes for your body to process half of it—is roughly five hours for the average person. But “average” doesn’t mean you: genetics, age, and body weight can make that range anywhere from 2 to 9 hours.

Across the studies, doses ranged from 50 mg (a cup of tea) to 600 mg (six cups of coffee). Participants drank caffeine anywhere from 15 minutes to several hours before bed.

Here’s what happened compared to people who had decaf or none at all:

Sleep Metric	Finding
Sleep duration	Caffeine drinkers slept 45 minutes less on average. Every hour earlier they stopped drinking caffeine added back ~3 minutes of sleep.
Time to fall asleep	Took 9 minutes longer to drift off.
Sleep efficiency	Dropped by 7%.
Deep sleep	Reduced by 11 minutes per night.
Waking after sleep onset	Increased by 12 minutes.

Even modest amounts—100 to 200 mg, about one or two cups of coffee—made a measurable difference.

The researchers found that timing mattered a little (earlier caffeine helped), but dose mattered a lot. 

For example, a 217 mg caffeine pill needed about 13 hours to clear enough to protect sleep, while a 107 mg cup of coffee required about 9 hours.

If your bedtime is 10 p.m., that means you’d need to finish your coffee around 1 p.m.—not bad news for morning drinkers, but a rude awakening for late-afternoon sippers.

Actionable Insights

1. Too much, too late = trouble. Even if caffeine doesn’t keep you awake, it can still fragment sleep and steal deep stages like REM. You’ll wake up feeling foggier, even if you “slept fine.”

2. There’s no universal cutoff. Some people can enjoy an evening tea with no problem; others need to cut off all caffeine before lunch.

3. Run your own experiment. Try moving your last cup earlier or swapping one coffee for green tea. Track how you feel the next morning. You don’t have to go cold turkey—just curious.

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Closing Thoughts

Fifteen years of coaching have shown me one clear truth: caffeine can be both a gift and a trap. It sharpens focus when used wisely—but steal too much from tomorrow, and your body collects the debt. I’ve watched clients transform their energy simply by cutting off caffeine a few hours earlier. They didn’t sleep longer—they slept better. And that difference changes everything: mood, willpower, recovery, even how you see the day ahead.

Your health is your wealth

— Michael Beiter

Personal Trainer • Nutrition, Sleep, Stress Management & Recovery Coach

References

1. Elsa-Grave V. et al. Cardiovascular effects of caffeine and caffeinated beverages - UpToDate 2025, Sep. Cited 2025 Oct 6.

2. Gardiner C, Weakley J, Burke LM, Roach GD, Sargent C, Maniar N, et al. The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Med Rev. 2023 Jun;69:101764.

3. Weibel J, Lin Y-S, Landolt H-P, Berthomier C, Brandewinder M, Kistler J, et al. Regular caffeine intake delays REM sleep promotion and attenuates sleep quality in healthy men. J Biol Rhythms. 2021 Aug;36(4):384–94.

4. Chinoy ED, Cuellar JA, Huwa KE, Jameson JT, Watson CH, Bessman SC, et al. Performance of seven consumer sleep-tracking devices compared with polysomnography. Sleep. 2021 May 14;44(5):zsaa291.

5. Driller MW, Dunican IC, Omond SET, Boukhris O, Stevenson S, Lambing K, et al. Pyjamas, polysomnography and professional athletes: The role of sleep tracking technology in sport. Sports. 2023 Jan 5;11(1):14.