We have been told over and over again that we need at least 8 hours of sleep a night. But is that really true? Well, if we believe the research from University of California San Diego (UCSD), it turns out that we do not need 8 hours a night. In fact, being a long-sleeper (sleeping 8 hours or more) might be harmful to your health and lead to an earlier death.
A large study published in 2002 showed that those who slept 8 hours or more and those that slept less than 4 hours a night had a much higher mortality rate than those who slept between 6.5 and 7.4 hours. This six-year study consisted of more than 1 million people between the ages of 30 to 102 years old. The study controlled for 32 variables, including diet, fitness level, age, etc. First author of the research, David Kripke, UCSD professor of psychiatry, stated that “we don’t know if long sleep periods lead to death” as correlation does not directly imply causation. However, “individuals who now average 6.5 hours of sleep a night, can be reassured that this is a safe amount of sleep. From a health standpoint, there is no reason to sleep longer.”
The study also noted that those who suffered from insomnia did not have a decrease in mortality rate but those who took sleeping pills regularly did. Remember, insomnia is not synonymous to short sleep. It just means having difficulty falling asleep and staying asleep.
This chart below from the study summarizes the correlation between sleep length and mortality rate:
From the chart, those who got around 7 hours of sleep had the lowest hazard ratio, which we can interpret as mortality rate. Those who slept 8 hours were 12 percent more likely to die in the six-year period than those who slept 7 hours. The interesting thing to notice here is to notice is that those who had 5 hours of sleep were even less likely to die in the six-year period than those who slept 8 or more hours. With that said, the majority of us cannot function optimally on less than 6 hours of sleep a night.
The University of California San Francisco found a family with a rare genetic mutation (hDEC2) that shortens their sleep cycle and allows them to function optimally. But they estimate that less than 3 percent of the population carry this gene. So for the rest of us, we need at least 6 to perform our very best.
Again, correlation doesn’t equal causation but this is pretty damning evidence against the oft-repeated advice of getting 8 hours of sleep a night. As a personal anecdote, I have found that I feel super refreshed if I get between 6.5-7 hours of sleep a night. This is because I wake up during the lightest part of my sleep cycle. And while there are minor variations, the majority of us will be at the lightest part of our sleep cycle at 6.5-7 hours of sleep too.
Director of the UCLA Center for Sleep Research, Jerry Siegel, stated that it is incorrect to correlate more sleep with being healthy. He explained that our ancestors (the hunter gatherers) slept just 5 to 7 hours a night. Thus from an evolutionary standpoint, we are naturally not long-sleepers (categorized as needing 8 hours or more of sleep). According to Roger Ekirch, a sleep historian, humans have slept in two four-hour blocks, which was separated by a period of wakefulness in the middle of the night lasting an hour or more. This pattern of sleep is polyphasic.
The Myth of 8 Hours of Sleep
It’s quite hard to track where the advice of 8 hours of sleep came from, but it has been quoted time and time again. If you go to Harvard’s website or The Sleep Foundation, you will see that they recommend 7.5 to 8.5 hours (7 to 9 in the updated guide) of sleep a night. The most likely answer as to where the myth of 8 hours of sleep came from is that The Sleep Foundation gave a recommended range of adequate sleep and then people just took the number 8 because it was a nice round number and then ran with it. Doctors told their patients. Mothers told their children. Husbands told their wives. But what is interesting about the updated recommendation from The Sleep Foundation is that they stated that even though adults need 7.5 to 8.5 hours a night, getting 6 hours is also okay. See the updated chart by The Sleep Foundation below:
The footnote notes that these recommendations come from six sleep experts and experts from the following organizations:
– American Association of Anatomists – American Academy of Pediatrics
– American College of Chest Physicians – American Geriatrics Society
– American Neurological Association – American Physiological Society
– American Psychiatric Association – American Thoracic Society
– Gerontological Society of America – Human Anatomy and Physiology Society
– Society for Research in Human Development
– American Congress of Obstetricians and Gynecologists