Does it matter what time you go to bed, if you’re getting the same hours of sleep?
In: Biology
It can. Sleep isn’t all about quantity, but also about quality – especially how much time you spend in deep sleep. Various mental and physical factors can cause a person to not sleep very deeply, and thus feel less restored during the day. What time you go to bed also plays into this. Your body has a kind of internal rhythm of sleep vs. wakefulness (mediated by hormones) which, amongst other things, gets entrained to the daylight hours. This means that, on the whole, it is harder to sleep – and sleep deeply – when it is light outside, even if you can make it dark in the place where you sleep. The exposure you get to daylight, or the lack thereof, outside of your sleeping hours, still synchronizes your internal clock to the day/night cycle. To some degree, anyway – your own sleeping habits and genetics also play a role in this. Some people by nature are “owls”, while others are “larks”, and if you habitually go to bed and wake up at certain hours, you will also tend to feel sleepy in between those times. Still, it’s harder to fight the day/night cycle than to follow it.
What this all means is that if you go to bed and wake up late, then even though you’re getting the same length of sleep as someone else, the fact that you’re sleeping into the day may end up reducing the quality of your sleep.
It also means that it isn’t helpful to vary your sleep times a lot. As I said, that internal rhythm also gets entrained to your own habits. If you go to bed late one day and early the next because you have an early appointment in the morning, you may find it harder to go to sleep when you want to, and then you’re having to wake up before you’re well rested. So the quantity of sleep may suffer too, but of course in the hypothetical scenario you posed we assumed it would be the same. Even so, varying sleep times also tends to mess up your internal clock, and so again that can lead to poorer sleep quality.
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