General guidelines for optimal sleep length
Although many people brag about only needing 4 to 5 hours of sleep, on average most people require 8 hours of sleep each night for optimal mental performance [2]. On an individual basis this can be somewhere between 7 and 9 hours for adults.
The recommendation of the National Sleep Foundation is a good basic guideline for age-specific sleep needs:
Generally, people exposed to a low-stress environment are at the lower end of sleep needs while people exposed to a high-stress environment – such as athletes – are at the higher end. Roger Federer and LeBron James are said to sleep 12 hours each night.
Sleeping 6 hours or less increases your mortality risk by 12%. Exempt are ~5% of the population with a genetic mutation on the gene DEC2 who get by fine on 6 hours of sleep without any health impairment. On the other hand sleeping 9 hours or more is also associated with a higher risk of death. However, no studies published to date have proven that long duration of sleep causes increased mortality. The reverse seems true: Long sleep is a result of by poor physical health, depression and other factors such as unemployment or low socioeconomic status.
If you are healthy and physically active, don’t worry about sleeping too much. However, in the absence of extraordinary stress or an infection continuously sleeping 9 hours or more might be a hint of undiagnosed diseases.
How to identify your individual sleep needs
The optimal sleep for each person differs, as it is influenced by individual factors such as age, genetics, mental and physical stress as well as your environment. It can even vary from day to day, depending on the amount of physical activity or mental stress you are exposed to or any infections you are facing. Therefore, plan 30 minutes more in bed than you need to allow your body to get all the sleep it wants to get.
The 3 principles of adequate sleep quality and quantity are:
- Short sleep latency: Fall asleep within 10 minutes in bed.
- No sleep disturbances: It is not normal to wake up because you feel the urge to go to the bathroom. (It is normal to wake up at night, though you should not be awake more than up to 5% of your total sleep time).
- Wake up naturally: Only use an alarm as a stopgap.
Some people have a strong wake rhythm and awake each day at the same time – independent of when they went to bed and how long they slept. Therefore above objectives not yet guarantee optimal mental performance during the day.
The final objective to achieve optimal performance:
- Best reaction time: Adjust your bedtime until you get your fastest morning reaction time.
Testing your reaction time at HumanBenchmark.com is an objective way to measure if you benefit from going to bed earlier and sleep more:
- Before you start the experiment, note your average sleep time per night and define your baseline reaction time by doing 5 tries of the test in the morning for the first 3 days. The average of these 15 results is your baseline.
- Now add 30 to 60 minutes of sleep by going to bed earlier.
- After 3 weeks repeat the 3 days of morning reaction time tests and see if you improved from your baseline. If you did, you now know that you benefit by getting more sleep than your old normal.
(This test is also the method of choice to evaluate the effect of any of the sleep tactics proposed in this article.)
It is important to note that sleep quality matters more than pure time in bed. 8 hours of poor sleep might be less recovering than 6 hours of quality sleep. The later discussed tactics to optimize sleep should increase your sleep quality drastically. You will feel more energetic and recovered with the same amount of sleep or even need less sleep than previously.
As most people neither sleep enough [2] nor accomplish above sleep objectives we will look at the mechanism of sleep and our biorhythm and ways to improve it.
You can read Part III here.
