Photo by Jacob Spetzler
Why is sleep so good for your brain, how much should you get and should you start panicking if you don’t get enough? We met Prof. Dr. Heidi Danker-Hopfe, one of Germany’s leading sleep experts, for a sobering chat about the science and secrets of sleep.
Truthiness, alternative facts, scare politics… When it comes to sleep, the media is filled with them. It is as if the late recognition of sleep as that precious part of our biological life had to come with scaremongering scenarios by self-appointed experts: sleep under seven hours a night and you’re predicted to get cancer, Alzheimer’s or a heart condition, unless it’s already made you obese and you are sure to die of diabetes anyway!
Meanwhile, the field of sleep medicine has been steadily growing, reflected by the number of accredited sleep labs (see right page). Patients get apnea masks and researchers win Nobel prizes for their work on sleep (last year, the award was handed out for deciphering the genes responsible for regulating our circadian rhythms). Add to that a thriving industry, from pharma pills to insomnia apps and even ‘weighted’ blankets that supposedly foster slumber… As that much-desired, brain-cleansing time in which our organism regenerates, sleep has become a must-have; can’t aff ord it, and it’s a disaster. As experts demand sleep be prescribed, should insomniacs lose more sleep in panic? Is sleep deprivation the silent killer? We asked Prof. Dr. Heidi Danker-Hopfe, leader of the sleep lab on Charité’s Benjamin Franklin campus in Steglitz/ Lichterfelde, to shed some light on the new, fascinating science that remains, in many ways, as great a mystery as the brain itself.
There are so many alarmist reports on how we don’t sleep enough. Do we really need to sleep eight full hours a night to be healthy?
The correct answer here is that you should sleep as much as you need in order to feel restored when you wake up. It really depends on the individual and varies with age. For the average adult, one person may need six hours to feel restored while another might need nine. Three years ago, American researchers reviewed an enormous bulk of literature on sleep duration and health impairment. They found that the optimal sleep duration is seven hours, but it remains a statistic.
An Observer article on recent findings in neuroscience reports that “adults sleeping only 6.75 hours a night would be predicted to live only to their early sixties”! Is there also an upper limit?
I don’t think the state of research in sleep medicine can prove that. The recommendation is no less than seven, but again it depends on individuals. Some might need less, whereas others need eight and a half and that’s also fine. When it goes up to nine hours, you have to check individually if there might be an underlying health problem.
According to a recent study by the TK health insurance company, 24 percent of Germans sleep less than six hours…
Yes, correct, but you have to take into consideration that they mostly surveyed a working population, and it’s a modern reality: people who have a regular day job tend to, on average, sleep six hours or less. Imagine, you have 24 hours in a day: you have full-time employment, so you spend about eight and a half hours at work including your break; add to that commuting time, which in Berlin can be up to two hours, so over 10 hours is spent on work. Then, you need to do the washing, you need to play with your children or with the dog. On top of that you want to have time to socialise and some time alone. And what comes at the very end? Sleep!
So what you’re saying is that our modern lifestyle is not sustainable. There are not enough hours in a day to achieve what we set out to do. But was it ever better?
Did people sleep longer 100 years ago, as some studies suggest? Well, when you don’t have enough light at night, and it’s dark after 6pm, what do you do? You go to sleep. So, one argument is that, due to the invention of electricity, we stay up later. But then, if you look at the scientific literature, there are also publications that suggest that sleep duration hasn’t really changed that much within a given culture. In the old days, people would go to bed earlier, correct, but then they would also wake up with the sunrise, so very early. Overall, I’d say that differences in sleep patterns are strongly cultural, they vary across the world: for example in Asia, they sleep less at night than Europeans do.
So are these recommended seven to eight hours of uninterrupted sleep a cultural notion?
The Korean and Japanese are known to be the shortest sleepers in the world… How do they do it? They need to work more, so they sleep less. But they also have different sleeping habits. Sleeping during the day, for example at work or on the train, is socially accepted. I have colleagues from Vietnam and they say that when at work, you can always put your head on your desk and take a nap. And if you collect enough naps over 24 hours you reach more or less the same amount as a full night. Same goes with sleep among the elderly. Many sleep less at night, but nap during the day, and if you add it up, it’s not that much less. Sleep duration varies with age, right? Recent studies show that teenagers tend to go to bed later and sleep longer, leading scientists to recommend a later start of the school day as a way to bolster performance in exams. What do you think? Again, I think we have to distinguish between biology and lifestyle. Teenagers go to bed late, so they have trouble getting up early, and they don’t perform as well in the morning. This has been confirmed by most studies. It is where the discussion to start school later comes from. What’s interesting is the reason why they go to bed late. Is there a biological reason for it, or do they simply not want to? And why is that? What can you do to adjust bedtime for better performance at school? And don’t forget the teachers – they might perform best at 8am!
How do you know that?!
It’s a small provocation (laughs). But as you grow older, you tend to go from an evening biological chronotype to a morning type. What I mean to say is that there will always be those who want to start later and the others who will not perform so well past noon, because they’re early risers and they get tired in the early afternoon.
By referring to ‘chronotypes’, are you confirming that biological clocks vary from one individual to another? That “night owls” and “early birds”, late sleepers and Frühaufsteher are not an urban myth?
Yes, some people are extreme morning types. They wake up at six, sing in the shower, and perform best early in the day. And then we see people who complain that they cannot wake up on time, and never manage to fall asleep before 2am. When they come to us, we first need to assess if it’s a lifestyle problem, an issue of time management, or whether it really is biological, namely a different circadian rhythm, that’s mostly genetic. Fortunately, we can measure this in the laboratory, thanks to one marker: our body temperature. The body temperature has a curve that varies +/- one degree along the 24-hour circadian cycle. And in late-sleeper chronotypes we can observe that the decrease in body temperature (which precedes sleep) takes place much later, which explains their problems falling asleep. Conversely, the body temperature of morning types starts decreasing pretty early on in the evening.
Morning types are better adjusted to the requirements of professional and social life. What can you do for the late chronotypes, the later risers? Can you help them change?
It’s difficult. We usually recommend that they adopt a fixed time to get up and to go to bed during the week. Light can help: use bright lighting in the morning to improve your wakefulness, and dimmed lighting in the evening, to trigger sleep by increasing melatonin (a substance that regulates sleep and wakefulness). But the easiest way is what one of our patients chose. She ended up dropping her 9am job for one more suitable to her sleep patterns: now she works evening shifts in a theatre, and no longer has a sleep problem!
Does this mean that some people might be more suited for night shifts than others?
Yes, there are some people who tolerate night shifts really well, and they correspond mostly to late types. Then some 17 percent of the population suffer when they work at night, what we call ‘night-shift syndrome’, which can entail digestive problems, and many other symptoms like headaches.
Is night work sustainable at all?
There are recommendations that nightshifts shouldn’t last more than 2-3 days, and that people should transition gradually from late shifts to night shifts. This is also a question of age. It gets more difficult as you grow older.
In the past, sleep wasn’t really taken seriously, right? As Shakespeare would have it, “there’s plenty of time to sleep in the grave”. Can you explain why we sleep and what we do while we sleep?
There’s a good quote by American psychiatrist Allan Hobson: “Sleep is from the brain, by the brain and for the brain.” So the brain is the most important organ for sleep but there are of course other physiological changes going on, such as a decrease in heart rate, a decrease in breathing frequency and so on. Meanwhile the brain gets involved at a very synchronized level, as expressed in brain waves which are of high amplitude and low frequency, meaning that neurons are acting in synchrony. When you are in this stage of deep sleep, that’s when the brain relaxes. And then there are always phases where the brain gets activated again. This is the REM (Rapid Eye Movement) stage sleep, the state in which you usually dream. There are other brain states associated with sleep stages, like very light sleep, which is similar to being awake and then there is stage two, when eye movement stops and brain waves become slower with only occasional bursts of oscillatory brain activity.
What’s the connection between sleep and memory? According to popular wisdom “learn your lesson just before sleeping and you’ll remember it!” Is it validated by science?
Yes, they say: “Put a book under your pillow and the next morning you’ll have it memorised!” And it’s true, and well documented, provided you’ve actually looked at your book before you went to sleep (laughs). It works wonders for young people, but not as well for the elderly. But then maybe sleep prevents them from forgetting even more.
Sleep also helps forgetting things, right?
Some people call sleeping ‘brain cleansing’. Yes, you filter out what’s unimportant. Memory traces during sleep are reactivated from deeper brain structures to the cortex and back, and that leads to memory consolidation. So stuff you haven’t practised or don’t think of as very important, gets forgotten overnight. Otherwise the storage in your brain would get oversaturated.
Here you treat patients with sleep disorders – I heard that with the advancement of sleep medicine you’re discovering new sleep pathologies every year!
When a patient shows up at our department, they either complain that the quality of their sleep is bad, or that they can’t sleep enough. We also have a group of patients who sleep the whole night and still feel very tired. Our role is to find out if the problem is the symptom of another disease or a disease in itself. For example, a couple of weeks ago, a young man called because he had “a sleep problem”. When we asked him to describe it, he said he needed up to 15 minutes to fall asleep, and then if he woke up during the night, it would take him five minutes to sleep again. So, in his own experience, he had a sleep problem. But for us, he’s a very good sleeper.
So sleep quality might just be a matter of self-assessment?
Partly, yes. We also had a 70-year-old complaining that he wakes up in the night several times and has trouble going back to sleep. We also have to be aware that sleep changes physiologically with age and is not the same at 70, as it used to be at 30. But then it can be a symptom of something else. We know that many diseases – cancer, neurological disorders, psychiatric diseases or any condition associated with physical pain, go along with sleep disturbances. If you treat the disease, the sleep problem will go away. Sleep problems may also occur while taking certain medicines. Take a look at the Beipackzettel of most drugs: how many list sleep disturbances among side-effects? If that’s the case, you might just need to try another drug.
Is insomnia an actual disease? Can you observe it through neuroimaging?
Insomnia is a class of diseases, numbering 60 that are divided into six different types. Insomnia in the narrower sense is also complex and there are many types: from not being able to fall asleep, to wakefulness at night, and so on. You can visualise insomnia in people’s brains: the arousal system is activated when it shouldn’t be. It might be related to stress, but it might also be genetic. Then some people lose sleep in situations where everyone would, like when you lose your job or a family member. So you need to understand what’s going on – is it a sleep disorder or something else? A good example here are people who have Night Eating Syndrome (NES). If you’re aware of your nightly snacking, you have an eating disorder. But if you eat at night and you’re not conscious of it because you’re asleep, then it’s a sleep disorder.
Is that somnambulism? When people sleep-walk to their fridge and start sleep-eating stuff?
Yes, and it becomes a problem when they start eating things which are not edible… Fortunately, these diseases are rare. So every time you get a patient here you first assess if it’s a sleep-specific problem, a symptom of another condition, or just a byproduct of lifestyle choices? Yes. Once, many years ago, we had a patient here and we found out that every night around 11pm he drank a big mug of coffee. We said please try to avoid it, and he was happy.
Is coffee that bad for your sleep?
It depends on individuals. Some people can drink coffee until late in the evening, and they sleep very well. Others need to stop in the early afternoon otherwise they won’t sleep. But then in nursing homes, they give a cup of coffee in the evening to residents who have problems falling asleep. The coffee remedies poor blood circulation in the brain, which stops them from sleeping in the first place.
What about alcohol?
Some people use it as self-medication when they have sleep problems. They’re like: ah, I’ll drink a beer or a wine, and I’ll sleep earlier. But the problem is that the quality of their sleep is not the same. And with time, to get the same effect, you need to increase your intake, so it becomes two, three beers…
You were just saying that punctual insomnia might be normal, which is nice to hear, because when you can’t sleep, you know you’ll be tired, and then not perform as well, and it just gets worse.
Yes, this phenomenon is called ‘Teufelskreisinsomnie’ – it’s a vicious cycle: you start thinking and it gets worse and worse. But part of the treatment is to make people aware that everyone sleeps badly once in a while, and that’s okay.
But what happens if you don’t sleep for days? Do we have a biological restorative mechanism or a catching-up system? In short: can your ‘sleep debt’ be repaid?
You can and will catch up. We can also measure how it works. For example, if you have one sleepless night, the physiological pattern of your next night’s sleep will be different: you tend to have more deep sleep than usual. So the recovery system works. It usually takes a couple of days though, depending on how sleep deprived you were. But it doesn’t work the other way around, to think ‘I’ll sleep more now, because I won’t be able to sleep much tomorrow.’ There’s no such thing as ‘credit in the bank’!
Can you train your sleep?
Yes, to some extent. Medical doctors train themselves to get some sleep in short intervals whenever they are able to. And, for example, I started training myself in power napping, as I drive long distances. When I’m driving and I feel I’m getting sleepy, I can go to a parking lot, sleep for 10 minutes and then I am completely awake again. I couldn’t do that 20 years ago, but now I can.
What do you think about the fast and efficient solution of swallowing a sleeping pill to combat insomnia?
According to German and European Guidelines, the first line of treatment against insomnia is cognitive behavioral therapy, not sleeping pills. The problem with sleeping pills is not only that you may develop a dependency. But also they induce a different sleep structure. With benzodiazepines, the most popularly prescribed sleep aids these days, we’ve observed that you don’t get much deep sleep; it mostly induces medium stage sleep through the night. So you sleep, but in a different physiological way.
What about melatonin? It’s sold over the counter in many countries and is very popular, as it has no obvious side effects. But does it work, or is it a case of the good old placebo effect?
The European Guideline does not recommend melatonin in the treatment of insomnia. Melatonin is a substance produced in the body in the evening when the light goes down. Hence the idea that taking it may help people sleep. The problem is that other physiological effects of the substance remain unknown and there are no convincing studies that show it really helps. So, maybe it’s more of a placebo effect.
Placebo works well, right?
Yes! Very well. It’s the same with phytopharmaceuticals, or plant-based medication. There are no studies that indicate they are better than a placebo, but they help. The placebo effect is really an interesting phenomenon, and we should use it.
So what about those alarmist claims that a lack of sleep is killing us? I mostly sleep six hours a night, like one quarter of German people. Am I condemned to Alzheimer’s, cancer or a heart attack by age 50?!
Interesting question! Sleep is related to Alzheimer’s but possibly more as a consequence than as a cause. We don’t know for sure. That sleep problems would induce cancer – there is no scientific evidence. As for cardiovascular diseases, I’d say the link might be more related to the stress factor: if you don’t sleep enough and are too stressed about it, then you are at risk. But, if you sleep only six hours a night and feel fine otherwise, there’s no increased risk. There are studies showing exactly this.
But there are hundreds of articles and reports claiming a clear link between cancer and sleep deprivation…
To my knowledge there was no conclusive study that indicated this. But it’s hard, what would be needed is a proper epidemiological study, and we do not even know how long it takes for a specific cancer to develop. And then, what would the ideal time frame to look at sleep be, and how to isolate and control other relevant factors?
More than two decades down the road since you started, what still fascinates you about sleep? It’s so linked to the brain and there’s so much we still don’t know about the brain. There are so many open questions. Why do we really sleep?
The question remains unanswered. For example, how long can a human being stay awake without dying? Some tests were made on animals, but we can’t even tell if it’s the stress of being kept awake or just being awake that prevails. You can’t find out in humans because, for obvious ethical reasons, we cannot conduct those experiments. We know about the restorative functions, but what would really happen to a human brain that doesn’t sleep? It’s not clear.
