How healthy or unhealthy is polyphasic sleep?
There’s little evidence either way, but I’m deeply skeptical that polyphasic sleep schedules are anything but a fancy form of chronic sleep deprivation. That’s pretty bad for you.Notice how many of those symptoms are difficult to detect. There’s no shortage of people on the Internet who will talk about how an Uberman schedule is great once you get used to it—but most of the time they’re just talking about how they feel, not taking any objective measure of blood sugar or immune function or cognition. There are lots of things that can make you not feel tired (exercise, bright light, stimulants) while still suffering from sleep deprivation and weird sleep schedules are probably one of those.*The reason to be skeptical is that no one has put forth a convincing explanation of how a polyphasic sleep schedule would supposedly reduce the total sleep time required. The explanations that have been attempted generally rely on the hand-wavy idea that polyphasic sleep increases the “efficiency” of sleep, which raises a number of problematic questions:If humans can sleep more efficiently without any ill effects, why didn’t we evolve to do it naturally? If we could sleep as little as 2 hours per day (Uberman schedule) our “natural” sleep cycle would be an enormous waste of time and energy, and make us needlessly vulnerable to predators. Therefore, there would be an evolutionary pressure to us the more efficient mode of sleep as our default, unless it had negative consequences that outweighed the positives.Why does increased efficiency require polyphasic sleep in the first place? In many cases, sleep deprived people actually do show some increases in sleep efficiency, like the REM rebound effect. But these changes are small and don’t fully counteract the effects of sleep deprivation. If a super-efficient sleep mechanism existed, why would it work differently from our other mechanisms for countering sleep derpivation which work equally well in monophasic and polyphasic sleepers?The simplest answer of course is just that polyphasic sleep is a form of sleep deprivation that makes you feel less tired than other kinds (perhaps due to modulating levels of sleepiness-signalling chemicals like adenosine)* Another hypothesis is that the people who succeed on these schedules simply have a very low sleep requirement in the first place.