Research Review: Can We Sleep To Much?

In this article, our expert Dr. Yu Sun Bin reviews: Can People Sleep Too Much? Effects of Extended Sleep Opportunity on Sleep Duration and Timing by Klerman EB, Barbato G, Czeisler CA, Wehr TA. 


1) What was the high-level summary of the research? 

People cannot sleep ‘too much’. The amount of sleep we get is regulated by the homeostatic and circadian systems which drive us towards a stable amount of sleep, provided we allow enough time for it. 

While we cannot sleep too much, we can spend excess time in bed. When given 12-14 hours of opportunity to sleep, healthy people can develop patterns similar to those with insomnia and take longer to fall asleep, wake more often in the middle of the night, and wake too early and be unable to go back to sleep. 


2) What did the study try to measure? 

The study measured objective sleep using sleep studies. The study assessed whether, when given long periods of time in which to sleep, people could sleep to excess, or if they would reach a stable point with a roughly consistent amount of sleep every night. 


3) How was the study undertaken? 

The authors of this study analysed data from two of their previous studies. 

In Study 1, healthy volunteers were given the opportunity to spend 14-hours in bed per night for 28 days; In Study 2, volunteers were given the opportunity to spend 12-hours in bed for 8 nights, with the addition of a 4-hour window for napping during the day. 

Neither study interfered with the sleep of the volunteers, apart from giving instructions that they should try to sleep during those windows of time. Both studies involved volunteers sleeping in research labs so that factors such as work and socialising did not influence how much volunteers slept and when they went to sleep and woke up. 


4) What did the study find? 

In both studies, volunteers slept more during their first week in the lab – on average, sleeping 2 hours longer than they did at home. However, the differences between volunteers were marked: some did not sleep more at all when given the opportunity, whilst others slept almost 6 hours longer! 

After the first week of extended opportunity for sleep, the total sleep time of the volunteers stabilised: on average, people in Study 1 slept 8.6 hours nightly, whilst those in Study 2 slept 8.9 hours on average. However, individual needs for sleep were very different: at one extreme, one volunteer stabilised at 5.2 hours of nightly sleep, whilst at the other extreme, another stabilised at 11.0 hours. These results show that during the first week in the lab, having protected sleep time was important for many of the volunteers to catch up on sleep. However, once they had caught up, their sleep stabilised and they tended to have roughly the same amount of sleep every night. This amount of sleep was unique to them.

Also important to note is that sleep quality decreased for many of the volunteers in these studies – that is, even though the same amount of sleep was achieved, it took them longer to fall asleep, they woke up more often or too early on some nights. However, unlike people with chronic insomnia, these healthy volunteers then made up for this slight sleep loss the next night. This is exactly how sleep is supposed to work as dictated by the sleep homeostatic process which maintains an equilibrium in our sleep/wake cycles. 


5) Is there any other research out there that supports these findings or contradicts it? 

There is plenty to support it! For example, in large scale epidemiological studies that link long sleep durations (>9 hours) to poor health, the association is no longer seen when existing health conditions are taken into account. This suggests that it is time in bed and poor sleep quality that contributes to poor health, or that poor health contributes to excess time in bed and poor sleep quality.

Similarly, in terms of performance, it is not possible to sleep more to ‘bank’ sleep, but it is possible to reduce existing sleep debt so that you are better protected from any effects of future sleep deprivation. 


6) How much weight should we give this research?

This research is highly credible given the supporting evidence. The only thing to keep in mind is that the studies were limited to young people, aged 18 to 36 years, without any health conditions so the expectation of ~8 hours of sleep being average may not be applicable to other age groups and people with existing health conditions.


7) What does this mean for your work/research/industry? 

There is often a disconnect and conflict in the sleep field about what advice we give to people with clinically significant insomnia and to the general public at large. The message we try to give to the general public is that typically, people should sleep more to get enough sleep. However, the clinicians who work with insomnia sufferers are unhappy with this message, because spending more time in bed can make insomnia worse. 

This study shows that there is a direct connection between those two messages and that they are actually not in conflict. That is, we should all try to sleep enough, for us to be individually well-rested, but avoid spending more time in bed beyond that point, because it only creates poor sleep quality that’s similar to symptoms of insomnia. 


8) What’s the key takeaway for us to take from this research?

It isn’t possible to sleep ‘too much’ but it is possible to spend too long in bed. If you spend too long in bed, the quality of your sleep can suffer. 


9) Will you be doing anything differently because of this research? 

I think this study highlights we should give ourselves the opportunity for enough sleep every night and try to figure out where our equilibrium point of ‘enough sleep’ is. We should then try to protect our sleep time to achieve our required amount of sleep as much as possible.


Dr Yu Sun Bin is an epidemiologist and public health researcher. Her particular research interests are on sleep and circadian rhythms and how these biological systems are reflected in behaviour, health, and disease.