The Sleep Optimization Problem

When humans mastered using artificial light to stay up past our natural bedtime, we arrogantly took conscious control of our sleep – a process that had previously been automatic and honed by millions of years of evolution. Out of the sleep strategies which emerged, two categories are now clear. The first maximizes the amount of time awake at a minimal functioning level, while the second maximizes performance while awake, and only limits sleep time after the performance benefits reach a plateau. Which of these strategies is best? And how should we decide when to go to bed, and when to set our alarms?
 
Sleep psychologists say that chronic sleep deprivation reduces health-related quality of life in both short and long term [1]. For those who care about health, the latter strategy definitely wins, although this boils down to a philosophical question of priorities. If there are things more important to you than health and cognitive performance, then you'll want to utilize polyphasic sleep techniques to minimize your time asleep. For the rest of us with more traditional values, let's figure out how to avoid this so called "sleep deprivation".

Sleep deprivation is often defined as sleeping less than around eight hours a night. Great! We know what to optimize for, and we know how to do it. Just set your alarm for around eight hours after you go to sleep (or go to sleep eight hours before your alarm is set), and not only will you feel good throughout the day, but you’ll also beneficially contribute to your long term health.

Unfortunately, like most things that are critical to human well-being, the situation is not that simple. Here are the issues.

1. Eight hours of sleep is on average the optimal required amount of sleep, but this sweet spot varies a great deal. If you stick to the traditional wisdom of eight hours a night, while your actual optimal sleep duration is 9 hours, you will end up with long term negative health effects and reduced wakeful performance [2]. Finding your own personal optimal sleep amount may be possible, but it will change over time due to environmental factors. Perhaps the best bet to stay fully rested is overshooting your estimated optimal sleep, even if this has a chance to waste a bit of wakeful time.
Except...

2. Overshooting does not work. Sleeping longer than your optimal sleep duration quite simply is associated with increased BMI, psychiatric disorders, and risk of all-cause mortality [3]. Note that the referenced study could not demonstrate causation, and it does seem plausible that already sick people would tend to sleep more. However, the parallels between these symptoms and those of short sleeping make plausible an opposite mechanism: any denial of the natural circadian cycle causes similar negative side effects. We don’t know for sure, so stick with not overshooting since the alternative has a >0% probability of causing negative health effects.

Hit your sweet spot, or suffer the consequences in wakeful cognitive performance and long term health. The two most obvious ways to reliably get an optimal amount of sleep are to either follow along with the directions of sleep experts for discovering your personal optimal sleep duration, or perhaps more elegantly: never expose yourself to artificial light after nighttime and return control of the process to nature, only waking or sleeping at the demand of your body.


1
Short and long term health consequences of sleep disruption
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5449130/

2
Estimating individual optimal sleep duration and potential sleep debt
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5075948/

3
The Risks of Sleeping “Too Much”. Survey of a National Representative Sample of 24671 Adults
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4165901/