Too much or too little sleep are both bad for our health, according to a new study - further evidence that it's our body clock that counts

Too much or too little sleep are both bad for our health, according to a new study - further evidence that it's our body clock that counts


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  • A new study suggests too little or too much sleep could be equally bad for your health.
  • People who slept for less than six hours or more than 10 hours had a higher risk of developing a metabolic syndrome, like high blood pressure.
  • Many sleep scientists believe there is no substitute for a regular sleep schedule.
  • But "regular" can vary, depending on whether you are a night owl, early bird, or introvert.
  • It might be that people are out of sync with their body clocks, rather than there being an optimal amount of sleep everyone needs to get.

Sleep divides people. Some believe there's nothing more important than getting the right amount of shuteye, while others would rather be doing anything else than lying down in bed.

It is fair to say we don't get enough sleep as a society as 50 to 70 million people in the US alone have a sleep disorder, and about a third of adults not getting enough hours.

But according to new research, it's both having too little and too much sleep that can be an issue. The new study from the Seoul National University College of Medicine, published in the journal BMC Public Health, looked at the amount of sleep 133,608 Korean men and women aged between 40 and 69 years old were getting, and what health problems they had.

Results showed that men who slept for six hours or less per night had a higher risk of developing a metabolic syndrome, like high blood sugar, high cholesterol, high blood pressure, and fat around the waist, than people who got eight hours. Both men and women in this group also had a higher chance of a larger waist.


But those who had 10 hours of sleep or more per night were not better off. Both men and women in this group were more likely to develop a metabolic syndrome too, and women in particular had a greater risk of excess fat around the waist.

The results are observational, and it can't be said for sure that the amount of sleep directly caused the health problems. But the study does add to the growing body of evidence about sleep and its impact on our health and well-being.

For example, some sleep scientists, such as Matthew Walker, argue that sleep is "not like a bank," and you can't make up for a lot of late nights during the week by sleeping in at the weekend. Essentially, if you sleep in longer at the weekend, your body might go through "social jetlag," because you're knocking your schedule out of whack by a few hours.

However, a recent study from the Stress Research Institute at Stockholm University slightly contradicts this idea. Researchers found that people who got five hours of sleep or less per night had a greater mortality risk than those who consistently got seven or eight. But also, if the irregular sleepers tried to make up for their lost sleep at the weekend, then their mortality risk was lowered again to that of the regular sleepers.

"The results imply that short (weekday) sleep is not a risk factor for mortality if it is combined with a medium or long weekend sleep," the researchers, led by Torbjorn Akerstedt, said at the time. "This suggests that short weekday sleep may be compensated for during the weekend, and that this has implications for mortality."


There is no substitute for a regular sleep pattern. But what "regular" means to different people can vary a lot. For instance, people have different chronotypes - or body clocks - which means they rise and feel sleepy at different times of the day. Messing with their regular rhythms can cause them to be groggy and unfocused, which is why some people are more chipper than others first thing in the morning.

Personality types can also be a factor. For example, introverts often require a lot more sleep than extroverts because they find social situations highly stimulating and thus exhausting, and they can suffer from an introvert hangover as a result.

The study from Seoul can't determine whether there actually is an ideal amount of sleep for optimum health, or if people aren't necessarily behaving in line with what their body clocks actually need - causing problems in itself. Either could be true.

What is clear is that if you feel like you need more sleep, you probably do, and it's up to you whether you allow yourself to have a few extra hours or not. But if functioning properly means lying in on the weekend every now and again, rather than powering through the exhaustion, your body will probably forgive you for it.