An interview with Prof. Jim Horne conducted by April Cashin-Garbutt, MA (Cantab)
Is there any evidence that we’re sleeping less than we used to?
There’s no solid evidence that we sleep fewer hours today than we ever did, this is something I have gone into large amounts of detail in my book, in my published papers and at a recent meeting at the Royal Society of Medicine.
It could be argued that in many ways our sleep has never been better, in the sense that our sleeping conditions, on average, are far better than they ever were. Once upon a time, your normal worker was probably sleeping in a damp room, sharing a lumpy bed, which was occupied by bed bugs and fleas. Today, we have a very comfortable sleeping environment with pocket spring mattresses, comfy duvets, orthopedic pillows, warm bedrooms etc.
It’s important to understand that simply judging sleep by its duration alone, is not a true representation of its quality. When comparing the quality of our sleep now to the past, our sleep is less interrupted and more profound.
On average, how long do adults typically sleep for?
Based on the work we and others have done, the average amount of sleep taken by healthy adults, in the UK and other parts of the world, is just over 7 hours per night.
Do we really need a minimum of 8 hours sleep a night?
There’s no evidence that 8 hours of sleep is the ideal amount to have, it’s nonsense, because half the population of this country doesn’t get 8 hours sleep, on average, and so that means that theoretically, half the population of this country all suffer from terrible sleep loss, which is not the case.
Again, it defies the point I made earlier, that sleep cannot be judged on its quantity alone. The quality is important too. The idea of the fixed ideal amount of sleep being 8 hours for everyone, does not allow for any naturally occurring biological variations between individuals, which affects the amount of sleep a person needs. And this varies from about 6 to 8 hours sleep.
Where do claims we used to sleep 9 hours a night come from?
The idea of 9 hours seems to trace back to a study done in 1913 on 2,692 schoolchildren by Lewis Terman and Adeline Hocking, who found, on average, 13-18 year-olds got 9 hours of sleep. In this study they were also looking at the correlation between the amount of sleep and cognition, and this appears to be where the idea of 9 hours of sleep came from.
There’s no other evidence that people did sleep 9 hours a night. There’s only been incidental circumstances that people in the 1930’s had more sleep than we do now. But this would be individuals that felt tired all the time and so they would have more hours in bed, but that evidence is circumstantial. It only implies that people wanted to have more sleep, there’s no evidence to support that in the 30’s people actually slept for longer than they do today.
Typically, when asked, people say that they would like more sleep, but then they are not willing to forgo waking activities in order to get these extra hours. Many studies that claim we need more sleep have used leading questions such as asking participants if they would like more sleep, and of course this is likely to receive a positive response.
How have attitudes in society changed towards insomnia? Is it now more socially acceptable to talk about being sleepy?
Yes, I think so. Even in recent generations, our parents and grandparents, health problems, including sleep, were kept a private matter. But today we are a more open society and prepared to tell people about our aches and pains, and problems sleeping.
However, although we are hearing more about those who suffer from insomnia, it is not necessarily a problem that is getting worse.
There is also a lot more variety and choice for self-medications readily available in high-street drug stores and chemists which people did not have before, 20 years ago. But simply because there is a high rate of sales of these medications, does not mean it’s getting worse, people used to resort to alcohol before such treatments were made available.
At a recent meeting at the Royal Society of Medicine you said that you don’t like the term ‘sleep debt’, please can you explain why?
The term ‘sleep-debt’ suggests that you have to repay all of the sleep that you’ve lost. But there’s no evidence that this is true and that if you go without sleep, you have to make it up hour per hour, minute per minute.
There’s a law of diminishing returns, we know that when you go without sleep it’s the quality of that recovery sleep that is important and not the hours you have. So for example, if you do without sleep for one evening and based on the argument that you should have 7 hours sleep a night, how many hours should you make up to recover? Is it 14 hours of extra sleep tomorrow night or over the next few days?
No, there is evidence that states, generally, only about one third of sleep lost is made up, so in this case 10 hours of sleep would be sufficient to make up for the sleep lost.
But it is also important to take into account the quality of sleep. The essential deep sleep occurs in the first few hours of the night and is largely for brain recovery. The two thirds of the sleep which you forgo is a lighter form of sleep and is dreaming sleep largely.
That’s why I think ‘sleep loss’ is a better term.
What’s the difference between ‘tiredness’ and ‘sleepiness’?
A good example is that many with insomnia are tired in the daytime but they are not sleepy. If you have lack of sleep, you normally suffer more from daytime sleepiness, as you might expect.
However, many people with insomnia do not experience this sleepiness, but instead they are tired in the sense that they are disengaged and have a loss of interest in things, feeling down and miserable. But not necessarily sleepy. It’s therefore important to differentiate the terms tired from sleepy, especially in sleep research.
The word tired is also associated with many other meanings, for example the paintwork looks tired etc. You cannot substitute sleepy in this context.
Those who suffer from this sleep problem are not necessarily falling asleep in the day to an excessive degree but are feeling tired, rather miserable and down. Those who suffer from insomnia experience a high degree of hyperactivity in the daytime, and can’t relax leading them to become extremely unhappy.
It is therefore important in the treatment for those patients not to concentrate on the use of sleeping tablets to knock them out and give them more sleep, but to try and deal with their waking issues that are affecting their waking life, in order to help them go to bed with a more relaxed state of mind and sleep better, for example cognitive behavioral therapy (CBT).
Those who describe their lives as tired and not sleepy, generally do not see much improvement from using sleeping tablets, because that’s only looking at part of the problem. Sleeping tablets are still very useful for a short term crutch, as many types of prescribed sleeping tablets can help patients relax at night time.
Do we only sleep when we need it, or can we sleep for pleasure too?
Of course we sleep for pleasure, just like we eat and we drink for pleasure, sleeping is the same. After a working week, people often sleep in at the weekend. This may of course be also making up for someone who has suffered from sleep loss during the week, but the idea that the only reason we ever lay in at the weekends and sleep for longer is simply to make up for sleep loss is unlikely.
If you have nothing to do all day and you are lying in bed, you will sleep much more than you would normally, that person is most probably not simply making up sleep loss.
There is a lot of evidence showing that animals, for example in zoos, which have restrictions to their normal waking activities in the wild, sleep for far longer. Even farm animals in barns in winter sleep much longer than they do in summer.
A study in Germany found that three toed sloths that sleep 12 hours a day in the zoo, slept only 8 hours a day when in the wild. This suggests that these animals are bored in the zoo, whereas for many animals in the wild, their day is spent looking for food.
How important is sleep quality?
I think that sleep quality is just as important as sleep duration. If I use the analogy of food to explain my reasoning, the weight of the amount of food consumed alone does not equate to the measure of the nutrition a person receives, and it is important to look at the nutritional value of the individual foods a person is consuming.
In the same way, our sleep will vary over the course of the night, whether it be the quality, or the type (deep or light for example) of sleep we are getting as well as sleep disturbances that may occur. These things are equally important as duration of the sleep itself and so again I think when we try to calculate an ideal amount of sleep a person should have, it is a too simplistic guideline.
Are daytime naps worthwhile? Can they be dangerous?
Daytime naps can be worthwhile and no they are not dangerous. At the Royal Society of Medicine meeting, it was mentioned that sleeping once per day continuously at night, like we do now, is a very unusual thing in our evolution and it has only become typical in the last 100 years since the industrial age.
Previously, people would have a first sleep and a second sleep, they would sleep for two or three hours in the night then wake up, say prayers, socialize and check the safety of their house etc. then go to bed for another half hour. This was much more typical.
In other parts of the world today, in hot climates, people quite often split their sleep, not quite in the same way but they have a sleep in the middle of the day or early afternoon because of the heat. This then means they can stay up later at night and enjoy the cool air for example. Their body clocks are adjusted to that so they will have a one-hour nap or siesta in the afternoon and consequently they sleep much less at night.
But if you’re not used to sleeping in the afternoon, once the nap gets beyond 15-20 minutes it develops into full blown sleep and the body gets confused because you are sleeping at the wrong time of the day and so you wake up feeling pretty groggy. A long sleep in the afternoon creates a type of jet-lag, sleeping while your body clock is telling you to be awake, similar to jet-lag making you feel thick-headed, groggy and miserable.
It’s therefore important to make sure your naps are less than 20 minutes and this can be quite refreshing, but once you go beyond that amount of time and you’re are not used to it, it’s going to be counterproductive because you will have this jet-lag feeling.
By my original definition we know that people who wake up after a long, occasional and unscheduled afternoon nap will wake up tired but they’re not sleepy and they can’t go back to sleep. They feel this tiredness of feeling a bit down, miserable, etc.
Should we be worried by how much we sleep?
The acid test for insufficient sleep, as I mentioned, is when you are sleepy throughout much of the day, not just simply a dip in the afternoon which many people experience, or sleepy at bedtime. But the acid test is to experience being sleepy throughout most of the day, which is indicative of inadequate sleep.
Nature has given us this mechanism of knowing how much sleep we need by the extent to which you are alert throughout the day, in a similar way we know how much food and drink we need.
These sensations of thirst, hunger and sleepiness are the consequences of not having enough sleep, food, or drink. You don’t need to be told to get more sleep, your body will tell you. Most people know how much sleep they need, rather than how much they would like to have.
A lot of people worry about their sleep and are concerned that they get less than the recommended 8 hours, although they might still get 6 hours of quality sleep. And that if they are not particularly sleepy during the day then they may be experiencing hyper-arousal and suffering from insomnia and that they are at risk of developing associated sleep deprivation disorders such as diabetes, or a kind of asthma disease etc.
However, there is evidence that the link between short sleep and physical disorders are generally only apparent in those people sleeping less than 5 hours a day for a very long period of time.
Despite not getting 8 hours of sleep a night, if you are getting good quality sleep and you do not experience excessive sleepiness during the day (perhaps apart from maybe a small afternoon dip) you are not going become overweight and develop a heart disease because of this sleep loss etc.
But for those that sleep less than 5 hours a day, this is a short amount of sleep, and this indicates that something is not quite right. The solution for short sleepers who are overweight with type II diabetes is not to take sleeping tablets to help them sleep but to talk to a diabetologist, who will suggest getting more exercise and thinking about their diet rather than sleeping for longer.
There is no evidence that people with type II diabetes will improve their condition by getting more sleep. It may help them, but it’s a secondary treatment compared with exercise and better diet for example. It is not as simple as recommending that short sleepers who have a disease should have sleeping tablets to extend their sleep. It might help them but that’s not the first line of treatment.
What evidence is there linking lack of sleep with diseases such as diabetes?
There are only extreme laboratory studies that link short sleep to the onsets of these diseases. If you get young people and restrict their sleep to 4 hours a night for 5 nights for example they do start developing changes in their glucose metabolism indicative of what could lead to eventual diabetes.
But in reality it’s impossible to comfortably reduce peoples sleep to 4 hours a night for 5 nights. They would get very sleepy during the day and become stressed by it, posing the biggest risk of this extreme sleep deprivation falling asleep during the daytime and killing yourself in a car accident, for example.
It is unlikely that if you take normal healthy 7 hour sleepers and restrict their sleep to 4 hours a night that the change in glucose metabolism is solely caused by lack of sleep, it’s more likely due to stress. In these studies, participants were required to lie in bed for the whole time whilst being kept awake, which is an extremely stressful environment. Extreme studies like this are not realistic to everyday life where people may be on 6 hours of sleep a night and they will be okay.
Sleep is something that we all need, which we should ensure that we get adequate sleep. But the biggest dangers of inadequate sleep are from excessive amounts of sleep deprivation and although it can lead to depression from insomnia, for example, it will take many years for this to happen and it is not always the case. There is also no solid evidence that the lack of sleep itself is the cause of the depression.
It is more important to consider the reasons why a person is suffering from insomnia and if it’s linked to stresses from everyday life, then that is where the treatment should be focused. Dealing with these thoughts and problems will give them a more settled state of mind prior to going to sleep.
There is a lot of fear-mongering going on and exaggerations of the consequences of inadequate sleep. But the acid test is whether you are sleepy to an excessive degree during the daytime. And that is nature telling you that you are not getting enough sleep or something is wrong with your sleep. If you may think you are not getting enough sleep, it might be that the sleep you are getting is severely disturbed for example and is of poor quality.
One of the worst causes of disturbed sleep, and is quite common, is impaired breathing throughout much of the night. This is typified by very heavy snoring accompanied by very disrupted sleep , neither of which the snorer is unaware of. But they wake up in the morning feeling very sleepy despite having just slept.
Where can readers find more information?
In my new book Sleeplessness: http://www.palgrave.com/gb/book/9783319305714
About Prof. Jim Horne
Professor Jim Horne has published widely in the scientific and medical literature on many aspects of sleep.
Having run the Loughborough University Sleep Research Centre and been the editor of the ‘Journal of Sleep Research’, his exploration of this intriguing phenomenon remains unabated.