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Finding the Sweet Spot: How Many Hours of Sleep Is Best?

by Dr. Robert Rosenberg, Medical Adviser to SoClean, July 29, 2020.


For optimal health and the longest life span, is more sleep always better? Surprisingly, probably not—but it’s complicated. 

When it comes to the relationship between sleep duration and mortality, epidemiologists think of a U-shaped curve.1 In the middle, with the lowest risk, are people who sleep around seven or eight hours a night, the amount considered “normal” sleep. As people move away from that optimal amount of sleep—either higher or lower—their mortality risk increases. Here’s a look at why that is and how you can nudge your own sleep patterns closer to the sweet spot.


Research has shown that short-sleepers, usually defined as those who get less than an average of seven hours of sleep each night, have increased mortality risk.2 And that makes perfect sense. Not getting the amount of sleep your body needs triggers the sympathetic nervous system, the fight-or-flight response. This can increase inflammation, inhibit your immune system, and increase the risk for cardiovascular disease, diabetes, and obesity among other negative effects.

Most short-sleepers should be sleeping for seven to eight hours a night but aren’t because of lifestyle factors, such as social pressure to stay up late, having to do shift work, or using electronics and bright lights late at night. This has a clinical name: behaviorally induced insufficient sleep syndrome. 

A lot of short-sleepers have convinced themselves that they just don’t need as much sleep as other people, but that’s pretty uncommon. It’s true that some people—perhaps 1 percent3 of the population—genuinely don’t need as much sleep, feel fine without it, and won’t be harmed by regularly getting less sleep than normal. But if you notice that you tend to get a lot more sleep on vacation, or even on weekends, that’s a good indication that you need more sleep all the time. 


It’s a little more puzzling that long-sleepers4—usually defined as people who sleep for more than 8½ or 9 hours a night on average—also have worse health outcomes. It’s not clear whether too much sleep is the cause of increased mortality, though. It’s possible that these people have other underlying conditions that cause both longer sleep and worse health outcomes. For example, depression can cause people to sleep longer, and some sleep disorders can lower the quality of sleep while increasing its duration.

Long-sleepers tend to have a higher incidence of diabetes, immune issues and obesity. But researchers are still studying the chicken-and-egg issue of whether long-sleeping is to blame for these outcomes or is just a side effect of them.

Normal sleepers

In the middle of the U-shaped curve, with the lowest mortality, are those who get a normal amount of sleep. That’s typically defined as around seven or eight hours per night, but it’s important to listen to your own body. If you get seven hours of sleep per night, for example, and still have symptoms of fatigue—such as moodiness, trouble concentrating or dozing off in the afternoons—that still may be insufficient for you.

Finding the sweet spot

When you find the right amount of sleep for your own body, you’ll notice that you’re more alert and have better focus. You’ll lower your risk of diabetes, heart disease, stroke and cancer, and you might even lose weight if you’re obese.

If you’re a short-sleeper—or even a normal sleeper still not feeling fully rested—getting all these positive effects might just be a matter of going to bed earlier and improving your sleep hygiene.5 For example, make sure your room is cool and dark, turn the lights and computer off well before bedtime, and try to go to sleep and wake up around the same time every day. 

If you’re a long-sleeper, on the other hand, it might be a good idea to check with your physician to make sure you don’t have any underlying health issues. Also, see a sleep specialist to ensure that you’re getting the best quality sleep possible. 

Finding the sweet spot for sleep means you’ll wake up refreshed, feel great all day—and likely even live longer.

  1. “Mortality related to actigraphic long and short sleep,” Sleep Medicine, January 2011. https://www.sciencedirect.com/science/article/abs/pii/S1389945710003023
  2. “Sleep Duration as a Risk Factor for Cardiovascular Disease- a Review of the Recent Literature,” Current Cardiology Reviews, February 2010. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2845795/#:~:text=In%20brief%2C%20recent%20studies%20suggest,the%20increased%20risk%20of%20CHD.

  3. “A tiny percentage of the population needs only 4 hours of sleep per night,” by Lydia Ramsey Pflanzer, Business Insider, November 2015. https://www.businessinsider.com/people-who-sleep-short-hours-2015-11

  4. “Who Are the Long Sleepers? Towards an Understanding of the Mortality Relationship,” Sleep Medicine Reviews, October 2007. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3755488/#:~:text=Increased%20mortality%20associated%20with%20long%20sleep&text=Most%20of%20the%20increased%20mortality,6.5%20hours%20in%20this%20study).

  5. Sleep Hygiene Tips, American Sleep Association. https://www.sleepassociation.org/about-sleep/sleep-hygiene-tips/