Is 7 Hours of Sleep the Magic Number?
If you’ve followed just about any media outlet the past week, you’ve probably come across this widely disseminated study on the optimal duration of sleep. By the way, you should be able to read the whole article, if you like, but it’s set up so you cannot print or copy it.
The study conducted in China looked at the habits of half million adults, mostly middle-aged or elderly and asked them to report on their average number of hours of sleep per 24 hours over the past 4 weeks. In addition, many other tests were conducted on some or all of the sample looking particularly at brain function.
The over-arching finding was a nonlinear relationship between sleep duration and cognitive decline and related brain imaging findings. Nonlinear simply means it’s not a straightforward relationship like sleep more hours and get a healthier brain. Instead, nonlinear means, if you sleep too few hours OR if you sleep too many hours, then either condition is linked to cognitive decline.
Nearly all media outlets reported in their titles or the first paragraph of their coverage that 7 hours is the magic number to overcome the brain dysfunction of aging.
Once again, and as stated here many times, this type of research suffers a major flaw that is not resolved by studying 500,000 adults. They could study 5 million or 50 million and get the same results but still suffer from the same fatal flaw.
By now I suspect you know the flaw. They gathered no objective data from the participants, for example sleep tests. Therefore, they have absolutely no way of knowing why anyone in the study slept 6, 7 or 8 hours or any other number. Someone could be sleeping 8 hours because of sleep apnea while someone else could be sleeping 6 hours because of an insomnia disorder. Without this information, we don’t know the real cause of the brain dysfunction, because I can guarantee it’s not simple a function of hours of sleep.
In other words, the 7 hours is a kind of signal, but a poor one regardless, because you could also have someone with sleep apnea or insomnia who sleeps 7 hours, yet still has cognitive decline and brain dysfunction.
The regrettable aspect of this study is this failure to make any mention of the lack of objective sleep data, which would have revealed the much more likely cause of cognitive decline and brain dysfunction. Thus, despite all the efforts of the researchers to bring important information to the scientific literature, instead they are leading people away from the diagnosis and treatment of sleep disorders, the more likely cause of their findings.