Optimal sleep duration – are most recommendations wrong? Basically, and I emphasize this again and again, I am glad when the media take up the topic of “sleep”. The more it is discussed, the better, because a lack of sleep is currently costing the German economy over €60 billion. Especially in this context, companies should understand that working hours are the No. 1 sleep killer. So … in principle, I am in favor of paying attention to sleep.
It only becomes problematic when the media simply adopt texts without questioning them or the studies mentioned. Of course, very few journalists can read studies, which is not necessarily their job per se. However, I think it would be important to have at least one expert in advance on the subject of the report in order to avoid incorrect or misleading communication.
Example: VOGUE – How many hours of sleep are recommended?
VOGUE currently has another headline on the topic of “Optimal sleep duration”. It quotes the classic study by the National Sleep Foundation, which I had already examined in more detail in an article from 2022 (see at the end under “Sources”). The core problem here is that it gives the impression that the specified number of hours (7-9 for adults) represents the optimal sleep duration, i.e. what our body needs. The result is that the average person who is woken by the alarm clock after 7 hours believes that their body has gotten the sleep it needs … because that is what the recommendation says.
However, there is only one sleep length that actually covers the sleep requirement:
Sleep in!
Anything else is always too little, because the body does not listen to the external clock, but to the internal clock. If you were to sleep for 8 hours biologically and wake up without an alarm clock (or other external stimulus), you would simply build up a 5-hour sleep deficit per week if you are woken up by an alarm clock every day after 7 hours. If you also fatally follow the recommendation mentioned in the VOGUE article to maintain this rhythm at the weekend, that’s already a 7-hour sleep deficit per week.
Over 70 % of people wake up with the alarm clock … in other words, all people who build up a daily sleep deficit that they never reduce if they don’t sleep in at the weekend. Maintaining a weekly rhythm therefore only makes sense if you also sleep in during the week.
Example: Study – 7h 18 minutes … optimal sleep duration against diabetes
Another study from Korea is a good example of a completely meaningless communication of a study result. A large observational study with around 23,500 adults investigated how sleep duration is related to sugar metabolism. The study was based on data from the US health study NHANES from 2009 to 2023. The result: the best values in terms of insulin sensitivity – a key factor for the risk of type 2 diabetes – were found on average with a sleep duration of around 7 hours and 18 minutes per night.
The researchers found a U-shaped relationship between sleep duration and metabolism. Both too little sleep and very long sleep times were associated with increased insulin resistance. The most favorable metabolic values were in the range of 7 hours and 18 minutes. This correlation was particularly clear in women and in people between the ages of 40 and 59.
It was also interesting to look at the so-called “catch-up sleep” at the weekend. If people sleep too little during the week, additional sleep at the weekend seems to be quite helpful. A plus of about one to two hours was associated with better metabolic values, which contradicts the statement in VOGUE. However, if there had already been sufficient sleep, a significantly longer weekend sleep – i.e. more than two additional hours – was more likely to be associated with poorer glucose utilization, which is an indication that a disorder is producing additional sleep requirements. But then this disorder is the cause, not the extra sleep, which is only a symptom.
You have to let it melt in your mouth that such a precise time is mentioned here as the optimum sleep duration, as if nature had set everything to “7 hours, 18 minutes”. The media titles communicate this accordingly.
What’s in the small print:
The authors emphasize at the end that this is an observational study. This means that it cannot be clearly concluded that a certain amount of sleep directly improves or worsens the metabolism. In addition, the information on sleep duration is based on self-reporting by the participants, which always entails a certain degree of inaccuracy.
The researchers also assume that the connection can work in both directions: A disturbed metabolism can worsen sleep – and conversely, poor or inappropriate sleep can in turn have a negative impact on metabolism.
Exactly this sentence is the important aspect, similar to “sleeping too much”. There is no causality between long sleep and glucose utilization, only a correlation. The chicken and the egg are simply bent in one direction for a headline. And that is exactly what I am accusing both the scientific community and journalists of doing here – putting the title before the truth.
Optimal sleep duration – Conclusion
I don’t want to bash journalists in this context, but I would like to raise awareness and at the same time encourage them to research such topics, which have a massive impact on health, more intensively. The optimum amount of sleep is only achieved by one parameter: sleeping in!
Interesse an mehr (kritischen) Themen zu Schlaf und Chronobiologie? Abonniert gerne meine „ChronoCoach-Update“.
Quellen
https://medicalxpress.com/news/2026-03-hours-mins-optimal-length-diabetes.html
VOGUE: https://www.vogue.de/artikel/wie-viele-stunden-schlaf-pro-nacht-nach-alter
