World’s largest sleep study finds that sleeping too much is just as bad for your health as not sleeping enough
01/08/2019 // Ellaine Castillo // Views

Most studies on sleep focus on sleep deprivation. However, there has been limited information regarding the possible consequences of sleeping too much. Scientists at the Brain and Mind Institute have found that those who slept less or more than the recommended seven to eight hours had poor cognitive performance compared to those who got just enough sleep. This finding was part of the preliminary results that the world's biggest sleep study released in the journal entitled Sleep.

The study, which involved more than 40,000 people from all over the world, used in-depth questionnaires and various activities that aimed to determine the effects of sleep as well as the lack or excess of it on a person's cognitive performance. Overall, there were 12 tests used in this study that evaluated aspects ranging from short-term memory to planning and executive function to communication skills.

"We really wanted to capture the sleeping habits of people around the entire globe. Obviously, there have been many smaller sleep studies of people in laboratories but we wanted to find out what sleep is like in the real world," said Professor Adrian Owen of the Brain and Mind Institute, who is also one of the authors of the study.

From their study, the researchers found that the optimum amount of sleep needed to keep the brain's performance at its peak is seven to eight hours. This is consistent with what doctors have been telling people for years. Unfortunately, nearly half of the participants slept less than 6.3 hours per night. What's even more concerning is those who had at most four hours of sleep had the cognitive performance of someone who was nine years older. Furthermore, those who slept for more than eight hours were just as negatively affected as those who had insufficient sleep. These effects of sleep were equally observed in all adults regardless of their age.


Among the different aspects of cognitive function, the researchers found that reasoning and verbal abilities were the most significantly impaired. Meanwhile, short-term memory was the least affected.

On a more positive note, the study also showed that a single night's sleep can significantly affect a person's cognitive function. This was based on the better performance of participants who slept longer than usual before the study compared to those who got the usual amount of sleep or more. So if you've got a big test or meeting coming up, make sure that you get enough rest at least the night before it.

Overall, the results of this study show that in order to achieve peak cognitive performance it is recommended to get seven to eight hours of sleep since anything below or above that can negatively affect these functions. (Related: Is too much sleep a bad thing? Evidence says there’s a healthful limit.)

Other health risks associated with too much sleep

If you love sleep too much and you're finding it hard to limit yourself to eight hours, consider the following health risks that have also been associated with oversleeping:

  • Chronic inflammation
  • Increased pain
  • Impaired fertility
  • Reduced glucose tolerance
  • Weight gain
  • Higher risk of heart disease and stroke
  • Increased mortality risk
  • Poor sleep quality
  • Headaches

Read more news articles about the importance of getting adequate sleep by visiting

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