Nutrition science is notoriously unreliable. The reason is because a substantial proportion of research in the field is conducted using surveys, and people just aren't very good at remembering what and how much they ate.
The field is further damaged by a sensationalist press, which breathlessly reports every study and converts minor findings into flashy, eye-catching headlines. The latest example of this is a study that linked increased coffee consumption to reduced mortality. In general, media outlets wrote headlines like, "Drinking coffee may reduce the risk of death."
Well, not exactly. A plethora of data shows that coffee probably has some health benefits. However, after reading the original paper, carefully examining the data, and applying a dose of common sense (all of which we did), headlines should probably have said, "Coffee is consistent with a healthy lifestyle." That's far more accurate but definitely not exciting, so nobody wrote that headline.
Sleep studies suffer from a similar problem. Consider the latest study to make the press. Here's how Business Insider covered it:
Okay, so we should all decrease our risk of dementia by getting plenty of sleep, right? Well, no, that's bad too. Reader's Digest warns us:
And just in case you aren't yet afraid of your bed giving you dementia, Harvard (yes, that Harvard) ran this headline:
Alright, then. Maybe sleep is sort of like a vitamin. We don't want too much or too little. So, let's stick to the 8 hours that doctors commonly recommend, right?
What's the Skinny on Sleep?
To be fair, many outlets (even the ones with sketchy headlines) get some of the science correct by mentioning all the proper caveats usually associated with sleep studies, such as correlation not necessarily equating to causation. But clearly, there is plenty of misinformation out there. What's really going on?
Most likely, too much or too little sleep is not causing health problems, but is rather an indicator of them*. It is easy to imagine that the same molecular changes that occur in the brain that lead to dementia are also responsible for disturbances in sleep behavior. In some people, that might manifest as too much sleep; in others, too little sleep.
So, how many hours should you sleep? It depends on you. If you feel fine on 6 hours of sleep, do that. If you need 9 hours to function properly, do that. It is highly unlikely that a single sleep recommendation can be made for all people.
The bottom line is that if you feel tired, your body is telling you something. Listen to it, rather than the media.
*Note: Obviously, sleep deprivation would be a cause of health problems.