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Hi! I'm Stelios Pantazis. I'm a doctor and I specialize in medical nutrition and metabolic disorders. Our subject today is sleep duration and how it affects our health. I'd like to present a study that was published in 2016 in one of the three most respectable medical journals, Nature. This study associates sleep duration with life expectancy. Namely, it studied how many years someone lives depending on the hours they sleep. As I said in the video on the ideal number of daily bowel movements, there are two ways to evaluate a health index such as the hours of sleep per night. The first way is to ask 100 apparently healthy people how many hours they sleep per night, and to consider the range of the hours of sleep of 97-98% of them as normal. This is the first approach and as I said in the video on the ideal number of daily bowel movements, this approach sometimes causes trouble. This is why it may not be the best approach. The ideal approach, as I said there, is to design a study that asks the participants how many hours they sleep per night, monitors them for a few decades and finds out who lives longer. This study would be really noteworthy and useful, because we'd be able to find out the ideal sleep duration in the long term for the maximisation of life expectancy. In plain words, how many hours people who live longer sleep. Fortunately, such studies have been carried out, in fact more than once. Recently, some researchers decided to gather all these studies and answer this question with the biggest certainty possible. The studies that were considered more reliable and useful were 35, and the participants were monitored for up to 25 years, while the sleep duration was recorded through a questionnaire in all cases. The results were entered in a graph that shows an Y-curve, which shows that the ideal hours of sleep are approximately 6-7. Namely, people sleeping 6-7 hours a night have the longest life expectancy, namely they live longer. Life expectancy starts to drop when the hours of sleep drop under 6, while for people sleeping more than 7.5 hours, life expectancy drops again. For example, people that sleep 3-4 hours per night have much shorter life expectancy than people that sleep 5 hours, and people that sleep 11-12 hours per night have much worse life expectancy than people that sleep 8 hours. One of the strong points of the study that is worth mentioning is that the study is based on data from thousands of people and on monitoring lasting up to three decades. This makes it very reliable. Another strong point is that this study is prospective, which means that sleep duration is recorded before the results. Namely, we first ask the participants how many hours they sleep and then we find out who live longer. This strengthens the study too. The main weak point of the study is the fact that the hours of sleep are those that the participants mention, namely there's no objective measurement with the use of a machine or a device that records the hours of sleep with absolute reliability, but we're based on what the participants say. However, before rushing to conclusions, we should bear in mind that we should be careful with such studies. Such studies don't prove causality, namely we can't say with certainty that more or less sleep shortens life. Something the decreases or increases the hours of sleep may also affect life expectancy, regardless of the hours of sleep. For example, someone who suffers from a severe disease and gets much sleep may die from the severe disease, and not because they sleep more. Moreover, someone may get little sleep because they're very stressed, which shortens life expectancy, and it may seem as though the short duration of sleep is responsible for that, while the main cause is stress. In such a case, the attempt to increase the hours of sleep may cause even more stress and bigger damage, while the solution is to deal with stress. In any case, if you deviate much from the range of sleep times associated with the ideal life expectancy, you have to find the reason why this is happening and improve the conditions as much as possible, so that they can be suitable for this valuable function of your body. If you thought this was interesting, please give us a thumbs up. Share it with people who you think might find it interesting and subscribe to our channel in order to get notified when we upload a video. You can also suggest subjects in the comment section. Thank you very much!

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