Why you feel so sleepy

Part of the reason you’re sleepy could be staying up too late last night. But the other part could be the way you were trying to get to sleep. If you were trying to read yourself to sleep with an e-reader, you were sending a conflicting message to your brain.

“People don’t realize that the e-reader is emitting light directly into your eyes, shining it directly into your eyes. Basically, it’s telling your brain that it’s daytime.”

Dr. Charles Czeisler ran a study over 14 days where participants checked into Brigham and Womens’ hospital to read themselves to sleep. For five nights in a row, some subjects read from an iPad before bedtime and the rest read from a printed book; then the following week they switched.

They were all hooked up to sensors to document not just how long they slept, but how well.

And the data shows that light from the e-reader tells the body that the sun is up.

“That suppresses the sleep promoting hormone, melatonin, which is also an anti-cancer agent. It shifts our circadian rhythms to a later hour.”

E-reader users took longer to fall asleep and dreamed less. The effect was the same as working the night shift.

Whereas printed books…

“The printed book doesn’t have these effects,” since they use reflected light, not direct light.

But you don’t have to give up your e-reader. You can get one that uses reflected light, like the original Kindle, or just switch your tablet to white on black, which cuts the amount of light considerably. Or just give the tablet to your spouse and have them read to you. Then it’s their problem.