Scientists disagree, but for a good reason
I got a parcel from Amazon with two books on sleep last week. Both written by well-known sleep specialists. Reading them one after another just proves once again that scientists can never agree on anything. The two books seem to be making the opposite claims. One says insufficient sleep is the cause of all possible diseases and we are a sleep deprived society. The other says, stop freaking out, you need less sleep than you think. It also cites the evidence showing that more than nine hours of sleep per night is associated with higher mortality. Who is right?
I will review the two books another time. Now I just wanted to show you how the same piece of evidence can be interpreted differently depending on your agenda as the author. Moreover, I could even argue that even though the opposite claims can't possibly be both correct, they can be both justified from the public health perspective.
It is true that some studies show a U-shaped association between the amount of sleep you get and health. Meaning that both sleep that's too short and sleep that's too long is linked to unfavorable outcomes. What should we make of this? It could be tempting to say: sleep just right, not too much, not too little, and you'll be healthy. But we could also say: no, this findings means that inadequately long and short sleep are a just a reflection of underlying poor health. Finally, if you are a little bit more sophisticated, you could venture to suggest that sleeping too little will damage your health (i.e. get more sleep if you care about your health), whereas sleeping too long is a result of an underlying health problem (sleeping less is not going to cure you).
So which interpretation are you going to offer in a popular health-related book? Well, depends on your goals.
If you are trying to promote better habits in people who are good sleepers, but sacrifice their sleep to watching Netflix, you would say:"See! Short sleepers have worse health, don't watch Netflix, go to bed!"
But if you are trying to treat insomniacs... Telling them that their inadequate sleep will kill them is not going to make your treatment program effective. Rather, you might turn occasional insomniacs into chronic insomniacs. So it is more tempting to say, "See! Long sleepers die earlier. More sleep is not necessarily better. You'll be fine!"
And however unscientific this might seem, I feel that both books are actually serving their respective audiences well. We do need to raise awareness about sleep as a factor in health. But we also need to help insomniacs stop worrying about their sleep deficit because these worries maintain insomnia. We just need to make sure nobody reads both books like I just did.