Seven is the Magic Number of Sleep Hours

As if you needed any further proof that getting a proper night’s sleep is good for your brain and your future cognition, we now know that seven hours is the minimum number of hours a human needs to function normally both the next day and into the future. But did you also know that getting more than eight hours of sleep can be just as bad for your brain as not getting enough?

Yup. That’s right. You can actually sleep too much.

Scientists have a name for these two cognitively-impairing types of sleep: short sleep, in which you sleep fewer than seven hours, and long sleep, in which you sleep more than eight hours. The healthy sweet spot is right in the middle: so 7-8 hours of sleep per night, no more, no less.

In fact, long sleep is associated with roughly 1.8 times the odds of developing Alzheimer’s Disease. Short sleep is associated with a 70 - 100% greater odds of cognitive decline through all types of dementias as well as Alzheimer’s Disease.

What does this mean for you? It means, quite simply, that you should set an alarm that gives you at least seven hours of sleep but no more than eight. Maybe even experiment with 7 hours, 7 ½ hours and 8 hours, and see which feels best.


  • Spira, A. P., Chen-Edinboro, L. P., Wu, M. N., & Yaffe, K. (2014). Impact of sleep on the risk of cognitive decline and dementia. Current opinion in psychiatry, 27(6), 478–483. doi:

Related Articles

Browse Topics