When should I go to sleep?

If you're getting the recommended 8 hours of sleep, does it matter when you get it?

“The time of night when you sleep makes a significant difference in terms of the structure and quality of your sleep,” said Dr. Matt Walker, head of the Sleep and Neuroimaging Lab at the University of California, Berkeley.

The ratio of REM to non-REM sleep changes through the night, with non-REM sleep dominating cycles earlier in the night and REM sleep kicking in closer to sunrise, Walker said. That means a late night could result in insufficient amounts of deep, non-REM sleep. As we discussed earlier, it's crucially important to get healthy amounts of both REM and non-REM sleep.

So how early do you need to be to bed to get enough of each type of sleep? Walker says there's a window of several hours, about 8 p.m. to midnight.

The best time for you, though, will vary.

Till Roenneberg, a professor of chronobiology at Ludwig-Maximilian University in Munich who studies the biological roots of sleep, says each person has a unique internal timing profile called a sleep chronotype that determines where on the scale from “early bird” to “night owl” we fall. Your chronotype is largely genetic.

When choosing your bedtime, try not to fight your physiology. The best bedtime will differ a little bit for everyone, but it's crucial that you pay close attention to your internal clock and what your body is telling you. As long as you're getting the recommended 8 hours of sleep, just focus on finding the time that works best for you.