Anna Gragert
September 18, 2015 10:46 am

If you’re already on your third cup of coffee (we totally get it —it’s Friday, you stayed up late last night binge-watching Friends, the snooze button still won’t erase the fact that you had to wake up at 6:30am this morning), listen up. New studies show that too much coffee might be the reason why you’re having such a tough time getting a full night’s sleep.

So, Science Translational Medicine just published a new study that may make you rethink about that refill. Now, we all know that coffee is not ideal for bedtime, but did you know that caffeine can harm your sleep cycles even if you drink it mere hours before bed?

It all has to do with body chemistry. You’ve probably also heard that bright light – such as that given off by TVs, laptops, and cell phones – is bad news after the moon rises. Why? Because it puts a stop sign in front of your body’s melatonin, which is the hormone/key that unlocks the door to dreamland.

With these two facts in mind, researchers conducted an experiment over the course of 49 days. The objective: to compare the effects of caffeine to the effects of bright light, in order to see which one reigns supreme when it comes to defeating our shut-eye.

As for the procedure, test subjects would swallow a caffeine pill (equal to a double espresso) three hours before their normal bedtime. Once their bedtime arrived, the subjects were exposed to bright light for an additional three hours. Then, they were observed in four different states: (1) caffeinated in bright light, (2) caffeinated in dim light, (3) un-caffeinated in bright light, and (4) un-caffeinated in dim light. Note: those who were un-caffeinated were given a placebo instead of the espresso-like pill.

The results: “The caffeine delayed their internal clock by 40 min, a shift about half as long as bright light, a stimulus known to robustly lengthen the circadian phase,” the researchers write. In other words, the caffeine was worse than the bright light, but together both caused a 105-minute sleeping delay (which sounds like the opposite of fun).

While all of this may sound like a horror story to those who love coffee, there is a bit of good news: caffeine can actually help those who need to reset their body’s sleep clock. For instance, if you’re suffering from jet lag and still want to get a good night’s sleep, you can use coffee to keep your eyes open until it’s time for bed.

The research team also wonders if caffeine can help those who don’t work a normal 9-5 shift – especially since companies can lose a ton of money if their workers aren’t functioning properly (i.e. awake).

When all is said and done, it seems like coffee is a great tool —when used in moderation. So, drink up! (But not too much.)

(Image via Showtime)

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