I’ve learnt a little about sleep cycles and remember that every 90 minutes is when we move through the 5 stages of sleep, but I’ve also heard it’s recommended to have 8 hours of sleep. Wouldn’t that make you feel drowsy if you’re interrupting the sleep cycle when you wake up after 8 hours?
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The idea of an 8 hour sleep cycle came around the time Henry Ford was changing labor practices. (For his own benefit but it did help some people.) Now the unions at the time were fighting for better work hours. This was the “2 cents for pouring metal in a factory 80 hours a week era.” One of the BIG slogans for workers rights was “8 hours of work, 8 hours of Leisure,and 8 Hours of sleep.” As an example of a fair work day for employees. It worked and it stuck.
There is no evidence saying people NEED a full 8 hours. Indeed everyone is different. I sleep best with 6 most nights. I have friends who do two four hour sleeps. I even have friends who just “sleep when they are tired.” In fact, up through Puritan times the norm was to sleep early. Wake up in the middle of night for a couple hours then sleep again till daybreak.
Sleep is mysterious piece of human physiology we don’t fully comprehend.
TL;DR: You don’t, industrial era workers lobbied for a more fair work day and “8 hours for sleep.” Was one of their demands that’s persisted through the years.
I took a few courses on sleep in college and as others are saying here, 8 hours is just a nice catchphrase for an average persons time in bed.
You’re right that you do want to wake up naturally at the end of a cycle, but sleep isn’t just constant cycles after another. Depending on what’s going on with you personally it takes time to fall asleep, transition from stage 1 to stage 2, how many REM cycles your body needs, if you’ve been sleep deprived, etc..
For example I know 7 and a half hours is ideal for me, but during times that I’m sleep deprived that number shifts.
In the end, “8 hours” is just a generic term, not a real recommendation. You should ideally just let your body wake up when it will, and track how long you as an individual tend to sleep for
1) How much sleep people need is varied, and the side effects of not getting enough also vary, so it’s hard to tell when someone is sleeping properly.
2) The idea of 8 (or 9 in some studies) of sleep isn’t about getting 8 hours of actual sleep, but accounting for you taking a while to fall asleep and give you enough time to wake up. I think the actually sleep is 6 hours with many studies – but people take time to fall asleep and then wake up in the middle of the night.
3) The undisputed ideal sleep situation is one where you wake up naturally – this ensures you are waking in the correct sleep cycle. Some alarm clocks use a gentle changing of the color of a light to get this effect.
There’s a natural variation in amount of time adult humans need to sleep, but 7-9 hours is now the recommended sleep length (but this varies by age). Even if we keep to the traditional 8 hours of sleep, your first sleep cycle (consisting of all sleep stages) is usually around 2 hours. The longer you are asleep, each cycle gets shorter, and the proportion of time spent in each sleep stage (N1, N2, N3, REM) changes, shifting to longer and longer time in REM/dreaming sleep. How groggy you feel when you wake up depends on which stage of sleep you were in when you woke up. At 8 hours, it’s often easier to wake up not groggy because even if you are in the middle of a cycle, you are more likely to be in REM/dreaming sleep which looks a lot like your awake brain leading to less grogginess, generally.
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Yes, waking up in the middle of a cycle may make you feel drowsy. Instead of aiming for 8 hours on the dot, schedule your sleeping hours to allow you to get between 7-9 hours. When you wake up somewhere between hour 7 or 9, that’s it, you’re good. Do this for a month or more until you know your sweet spots for sleeping and waking.
8 hours is just a rough estimate of what’s needed. Most people need at least 7 hours, some need as many as 10. A small minority of people can actually maintain good health by sleeping 6 or fewer hours. The science behind this is compelling and I highly recommend you either read Dr. Matthew Walker’s book ***Why We Sleep*** to learn more about what happens in these cycles (especially the latter ones that only occur after several hours) or head to YouTube and watch a few of his interviews and presentations. On whichever podcast platform you use, search his name and listen to his interviews there, too.
What you’ll discover is while a few people can enjoy longevity and good health on less than 7 very few actually do. Sure, they may think they are fine with 4 or 5 hours sleep, but in the long-term many develop cancer, heart disease, Alzheimers and more after years of neglecting their bodies in such a way.
There’s three key ideas regarding your question.
The first is that humans generally need 7-9 hours of sleep. 8 hours is just an average.
The second is that sleep cycles average about 90 minutes. But…
The third is that as we get closer to waking up (assuming you have normal sleep and are not in sleep deficit) the cycles no longer enter deep sleep phases. Waking up in deep sleep is what makes us feel groggy most of the time.
The time on the cycles isn’t *exactly* 90 minutes. The time will vary per person – and per cycle.
Some people can feel refreshed after a 30 minute power nap… others can sleep all day and not feel refreshed.
Everyone is different… find what works best for you.
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there is a lot of misleading information in here. if you want to learn more about our current understanding of sleep from a laymans perspective i urge you to watch a few Matthew Walker videos. i like the Joe Rogan one, but there are plenty of others including TED talks. few youtube videos have made me pause and reevaluate my self like his have.
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