Why Caffeine Doesn’t Affect Everyone the Same Way
It turns out, our ability to handle caffeine is a bit like having a superpower—or, for some, a kryptonite. According to a June 2018 report from the Institute for Scientific Information on Coffee (ISIC), your sensitivity to caffeine partly boils down to a liver enzyme called CYP1A2. While that name sounds like a secret code for a spy mission, it’s just the scientific way of saying ‘not all bodies break down caffeine the same way.’ This gene varies widely between people, and, as the report explains, folks can generally be sorted into two groups:
- People with what’s called a slow metabolism
- People blessed (or cursed?) with a fast metabolism
Those with a fast metabolism process caffeine quickly, so the kick fades faster in their system. For slow metabolizers, caffeine lingers longer—and its effects are stronger. As J.W. Langer, a professor at the University of Copenhagen and report author, puts it, fast metabolizers can safely grab « several cups of coffee a day » without much trouble, as their body is quick to clear out the caffeine. On the other hand, for those less genetically gifted, « the physiological effects of caffeine last longer and are more pronounced ».
The Golden Hour: When to Stop Sipping
So, when exactly should you call it quits with your cup? For this, let’s turn to Dr. Reardon, speaking to Well and Good, who sets out some pretty clear limits. People with a fast caffeine metabolism should aim to drink their last coffee no later than 5:00 pm (that’s 17:00 for the 24-hour clock crowd). He points out:
« Let’s not forget that even with a fast metabolism, you can experience a cumulative effect from the other cups you’ve had earlier in the day. This might slow down your ability to break down caffeine later. »
If you’re of the slow-metabolism camp, you’ve got to be even more cautious. According to the expert, your final caffeine fix should be between noon and 2:00 pm. The reason? « It often takes at least eight hours to metabolize the caffeine in a single cup. » That’s right—even your innocent early afternoon espresso can haunt you deep into the night.
Science Puts Coffee to the Test
Curious how this all plays out in real life? Researchers decided to test caffeine’s effects on sleep with a rather creative experiment. For four days, twelve people with normal sleep patterns were asked to skip coffee entirely—no small ask! Instead, they took capsules at different times: sometimes containing 400 mg of caffeine (roughly equivalent to two to three cups of brewed coffee), sometimes a totally inactive placebo. Volunteers didn’t know which they’d taken.
Here was the routine for the first three days:
- First pill: six hours before planned bedtime
- Second pill: three hours before
- Third pill: right at bedtime
On day four, all three capsules were just placebos—giving researchers a baseline for a caffeine-free night.
No Late Coffee: The Proof Is in the Pillow
The results spoke volumes. The experiment confirmed what coffee skeptics have claimed all along: caffeine, when consumed too close to bedtime, seriously messes with your sleep.
« In the experiment, even when taken six hours before bedtime, caffeine reduced normal sleep time—participants slept on average one hour less compared to a night after a caffeine-free day. »
This was the first real proof that an afternoon coffee can genuinely hurt your quality slumber. Even more surprising? « This loss of an hour’s sleep went completely unnoticed by the participants, who said they felt like they’d slept as usual. » Just because you don’t feel sleep-deprived doesn’t mean caffeine hasn’t snuck in and stolen your Zzz’s!
Something to ponder next time you reach for that end-of-day cup: your body, genetics, and taste for deep sleep might not always see eye to eye. If you want to protect your nighttime rest, it might be time to set a hard stop for your coffee habits.
Also worth discovering: There’s a drink out there that scientists say can prolong your lifespan and protect your heart… And chances are, you’ve had it at least once!
John is a curious mind who loves to write about diverse topics. Passionate about sharing his thoughts and perspectives, he enjoys sparking conversations and encouraging discovery. For him, every subject is an invitation to discuss and learn.
