Why Late-Night Caffeine Is An Even Worse Idea Than You Thought

Photographed by Alice Gao.
As much as we know it'll keep us from getting to sleep, sometimes we can't help having a little after-work coffee. But a small new study confirms that habit may indeed be a Very Bad Idea — and suggests it may leave our sleep disrupted for even longer than we thought.

For the study, published earlier this month in Science Translational Medicine, researchers messed with five people's sleeping habits. Over the course of approximately 49 days, participants received a pill containing two espressos' worth of caffeine, a placebo pill, and bright light exposure beginning three hours before bedtime — the three conditions were tested at different times so the researchers could compare reactions within the same subjects.

Results showed that, after the caffeine pills, participants experienced their usual melatonin peak 40 minutes later than normal, which suggests the caffeine shifted their circadian rhythms. And, when looking at cell cultures, the researchers found that caffeine interfered with adenosine receptors, which are partly responsible for regulating another piece of our circadian puzzle. So it's not surprising that caffeine's meddling here can keep us awake. Still, the effect was less than half of the 85-minute shift that light exposure caused.

Unless you're battling a bout of jet lag, this seems like yet another reason to hold off on caffeine near bedtime. Participants in this study were given their caffeine doses three hours before they went to bed, and other research suggests holding off on those jolts for at least six hours before your head hits the pillow. Since caffeine sticks around in your body for up to 14 hours, less is probably more.

On the flip side, there is definitely a right time to drink that joe. Because your levels of the alerting stress hormone cortisol also ebb and flow throughout the day (and are counteracted by caffeine), you want to plan ahead to get the most energy out of that cup. Try to get your caffeine fixes between 9 a.m. and noon, when our cortisol levels are naturally lower.

Or, if all of that scheduling sounds like too much work, you can try out some Counting Sheep Coffee. Since this caffeine-free stuff contains valerian root (a natural sedative), you can get your evening coffee fix without sacrificing your sweet dreams.

Correction: This piece has been modified to correct that cortisol levels are lower, not higher, between 9 a.m. and noon.
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