LOUISVILLE, Ky. — So, story time.  About two years ago, my mom bought my brother-in-law and I some snazzy smartwatches for Christmas.  At the time, she thought our competitive natures would lead to battles over calories burned or miles ran or something like that. 

But, actually, a different feature ended up proving more interesting for our two-man Olympics: the sleep tracker. Much to my brother's chagrin, we always found that I would sleep up to two hours less than him, but our amount of "deep sleep" (at least according to the watch) would always be about the same.

Why do some of us seem to sleep better than others?  And why do some of us need more hours of sleep to feel good the next day?

I turned to Dr. Mohammed Saad, the Medical Director of the Sleep Lab for the University of Louisville. He says that the general population can be broken down into three groups when it comes to sleep needs.

Dr. Mohammad Saad
WHAS

The majority of the population, about 80-85%, need about 6 to 8 hours of sleep. "Short sleepers" account for 7-10% of the population and can work just fine off of 4-5 hours of sleep. The remaining 7-10% is the "long sleepers" group - the ones who need more than 8 hours of sleep and can sleep for 9 or 10 hours.

So, most of us are normal; we need the recommended six to eight hours each night. Yet some of us are blessed and can power sleep and meet our needs in less. Why?

Honestly, it's just the way we're built. Dr. Saad says it's probably a combination of genetics and early development as a kid. 

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These same factors can also explain why some of us fall asleep and stay asleep easier than others. Some of us are pros at napping while the sun's out and could sleep through twelve lawnmowers running at once outside our window.  Others wake up when the air conditioning hum is just a little too loud. Again, it pretty much comes down to the way we're made.

And, sorry to tell ya: training yourself to be a deeper or shorter sleeper really isn't a thing.  If you think you've successfully done so, you're probably kidding yourself. 

"This is how you've been born...This is how it is," Dr. Saad said. "You just need to figure out for yourself how many hours your body needs." 

He says that if you wake up feeling rested and refreshed, then you got the amount of sleep your body needed.  You can also conduct your own experiment by falling asleep, without an alarm set, and see how many hours you end up staying asleep.  Do this a few times, and--barring some other issue that is keeping you from staying asleep--you'll start to get a good idea of the amount of sleep your body naturally needs. 

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Now, all this said--and even though much of sleep habits are based in genetics and early development--that doesn't mean you need to accept poor sleep as your reality.

Dr. Saad wanted to make this clear: if poor sleep is leading to things like confusion, memory loss, anxiety, or depression, you should see a specialist because there are things they can do to help you get the sleep you need.

Oh, and by the way, I also asked Dr. Saad how accurate smartwatches are at capturing the quantity and quality of your sleep. His answer? "They're accurate to some extent. They're not 100%."

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