Can Sleeping Too Long Cause Dementia?

Here’s an interesting study that supports my explanation for how untreated sleep apnea can cause or aggravate Alzheimer’s. In this month’s issue of the European Journal of Neurology, researchers from Spain followed over 3000 volunteers for about 3 years on average, and found that people who reported sleep duration longer than 9 hours had over 2x the risk of developing dementia. They found increased risks as well for short sleepers (< 5 hours), but after adjusting for other factors, the risks was only slightly raised. 
They go on to report that about 70% of their study subjects were found to have Alzheimer’s as a cause of their dementia, and the rest had Parkinson’s, secondary dementia, and other/unknown. Within the Alzheimer’s group, both long and short sleepers were found to have significantly increased risk for having dementia. The authors of the study do propose that one possible explanation for this observation is that an underlying obstructive sleep apnea condition could be responsible, in addition to other various possibilities. They also mention another study that showed that daytime sleepiness was associated with increased chances of dementia after 3 years.
What this study implies is that if you’re not able to sleep effectively, you’ll naturally want to sleep longer to compensate. I doubt sleeping longer per se can cause dementia, and the study authors agree on this point. Having untreated obstructive sleep apnea for decades can definitely not only damage your brain cells, but can also make you tired during the day and cause you to sleep longer than normal. I’ve gone into much more detail about the link between sleep apnea and Alzheimer’s here, here, and here.
Here’s another prediction: If you sleep longer than 9 hours, I’m willing to be that you probably don’t like to sleep on your back. You’ll prefer to sleep on your side or stomach, right? And even if you do sleep for 9-10 hours, you still feel tired in the morning, right?

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