Sleep duration is an interesting thing.
The conventional wisdom is that all people need X number of hours a night, and that less than that destroys health. As with so much these days, the conventional wisdom assumes many wrong things, applies the wrong measures and then is applied universally with a broad brush. People are treated as if all people’s genetics and physiology is the same. They aren’t. They are also treated as if age, gender, health and nutrition were unimportant. Each is important in modifying the ‘correct’ answer.
Some people have a known particular genetic mutation in the BHLHE41 gene (rs121912617) that causes them to sleep on average 6 hours a night. They are called “Familial Natural Short Sleepers” (FNSS). Yet despite their being fully rested and in perfect health sleeping 6 hours a night, they are still classed (wrongly) as having a disorder. It isn’t a disorder. It is a fundamental difference.
Also critically important is how long each persons natural sleep cycle is. Typically, most people go to sleep fairly quickly after some short delay, then go through the classic cycle through deep REM sleep, and return to near wakefulness about 90 minutes later. They then repeat that cycle through the night, occasionally having to fully or near fully awaken to attend biological needs and return to sleep. The cycles become progressively less deep through the night.
For most people 5 or 6 cycles suffice. For some, like the FNSS, fewer cycles are needed. For others, more are needed. Breaking the last cycle and arising from mid cycle is the worst outcome. That messes with the natural circadian rhythm and hormones in deleterious ways. Doing that then creates less alertness and poorer performance, which people try to offset with stimulants. This all can then disrupt the next nights sleep.
If carried on routinely this can have serious health consequences. It is far better to forgo that last broken cycle entirely. However, lacking any knowledge of this, most people rely on alarm clocks and routinely break their last sleep cycle. It takes just a little knowledge, experience and planning to change this and to reap great benefits from doing so.
In my case, I routinely sleep 4.5 or 6 hours a night. I happen to have the FNSS mutation. I also sleep as my body needs based on health and other factors. As a result at times I sleep less. I have gone for as long as 9 months sleeping 3 hours a night, because that was all my body needed or wanted, with absolutely no deleterious effects. I have also had times that I required 9 or even 10.5 hours s night, due to illness.
Each persons natural sleep cycle is different. These are often about 90 minutes. And they tend to shorten slightly with each cycle. However, some people are quite a bit off of 90 minutes. Certain deep meditative techniques can alter the cycle length and pattern. And doing meditation during the day can reduce the amount of sleep needed.
As others have noted, our natural diurnal circadian driven clocks do not all precisely match the 24 hour clock cycle. People whose natural day is slightly longer will typically stay awake later and later each day ultimately becoming night owls. Folks whose day length is less will awaken early as their natural cortisol production kicks in, and go to bed earlier, becoming larks.
Another factor that plays in all this is LED lighting, TVs, computers, pads, phones and other devices. All of these now emit very bright blue light. That is most often at about 452 nanometers in wavelength. And that is perfect for activating the intrinsic cells in the eye (IPGRCs) whose function it is to detect daytime, and which when activated strongly suppress melatonin production. This then prevents or at least strongly suppresses the body going to sleep. Very little blue light is needed to activate the intrinsic cells. And strong activation can have a residual suppressing effect for two to four hours after the light is gone.
This then messes with sleep which messes with immune function. The result is much poorer performance the following morning, and day, and dramatic (up to tripling) increases in hormone sensitive cancers (breast and prostate), and large increases in cardiovascular diseases, obesity, type 2 diabetes, depression, suicide and more. These in turn can then drive the body to need more sleep for maintenance and recovery.
Using any “white” (most often blue and orange actually), or blue LED devices, even at very low brightness can severely disrupt sleep. Even incandescent lamps, which have the least amount of blue, can have an impact. Fluorescent lamps are bad as well.
With the mass conversion to LED lighting globally “to save energy” street lights are also converting. Even low levels of that light entering a bedroom or sleeping area can seriously disrupt sleep. There are other severe problems beyond these impacts. In the end, these lights will likely be huge drivers for ill health, increases in deaths, and productivity losses. These will carry with them energy costs that will likely fully negate the seeming reductions from simple electrical efficiency. Unfortunately, our societies don’t measure life cycle impacts. We base almost all decisions on short term capitol expenditures, “profit” measured in particular ways, and excluding all sorts of under valued, devalued, or messy non-enumerable costs (externalities like the climate and the environment, or people’s health).
Then too, the conventional wisdom also omits what we have learned from many native cultures. Studies of these people mostly untouched by technology reveals that they often are in bed 10 hours or more, but only actually sleep 5 to 6 hours. And that is often broken into segments.
So the question about “how long do we sleep” is actually a loaded question built on a serious set of errors. How long per se is not really the right question, or even a particularly meaningful one. And the right answer for each person varies with context of all of the above, with health changes (including breathing changes leading to use of cpap’s ... ), nutrition, family context and more.
Add to that that this is not a contest. The “winner” isn’t the person who sleeps most or least. Though our society really likes to frame things that way. The winners are those people who get the right amount of sleep that their bodies need.
