Tick tock body clock
What exactly is a body clock? And why do these clocks differ between people? Malcolm von Schantz is a body clock expert from the University of Surrey, and he spoke to Katie Haylor...
Malcolm - I think we need a cultural change in that we need to recognise sleep as time well spent. One interesting example of that is going from the American East Coast to Europe and you have a choice between taking a day flight and a night flight. Ninety percent of people will take the night flight because oh, that will save myself a day, but actually the night spent in your own bed at the end of that day is worth a lot. So, I think we need to schedule sleep and plan for sleep just like we plan for waking activities.
Katie - A very rough guide is you need to get about eight hours of sleep a night. But that's a big oversimplification and it varies between individuals, so why does it vary?
Malcolm - Well it varies as almost any biological factor varies like our height, for example. So, there will be a certain component which is genetic, and a certain component which is environmental. We use the term heritability to describe the part of the natural variance which is created by genetic variability so that could vary from zero percent to a hundred percent. Now if we look at some key factors relating to sleep, we can actually analyse this heritability by either comparing twins, identical and non-identical twins, or by looking at extended families. For example, sleep apnoea has about 25 percent heritability; insomnia has about 20 percent heritability; preferred bedtime and rise time it’s about 40 percent heritable; how much sleep we think we need has a heritability of about 30 percent.
But what is really stunning is what we call the sleep architecture, so that is the pattern of brain waves that your brain produces during sleep, that creates a very very specific fingerprint. Brainwaves, or what we would call an electroencephalogram, so this is something that you can study by putting electrodes on the scalp of the person, measuring the patterns of electrical activity during the brain which we can do in different stages. And in sleep, the pattern of neuronal activity changes very very specifically and very dramatically, and what is really striking is that exactly the pattern of these brainwaves, if you will, is very very specific to the individual. 96 percent of the sleep architecture, as we call it, of an individual is determined by genes and is actually your individual inherited pattern. And it's almost like a real fingerprint in that it can actually, with very high confidence, then be attributed back to the same individual again. So, we all sleep in our own individual, and in subtle ways, unique way.
Katie - Where does this concept of the body clock come in then?
Malcolm - So the body clock is a clock which ticks away inside our bodies and inside our cells and keep internal time, in principle independent of the 24-hour day and the change between day and night around us, that actually helps our body to anticipate the changes which occur across 24 hours of a day and the night, rather than reacting to them. So for example, our body clock makes us prepare for waking up even before we wake up, so it raises our body temperature, it brings up our blood pressure, it brings up levels of certain hormones so that even before we actually physically wake up our body has already started preparing for wakefulness. And a similar thing happens in the evening that the body clock starts essentially preparing you for the night. And this body clock essentially interacts with what we call this sleep homeostat, which is the body's way of counting your sleep need. So as we wake up in the morning and obviously we hopefully will have had a good restful night's sleep and then over the day we will accumulate what we call sleep pressure that will be maximal in the evening and that will make us sleepy, and then as we sleep this sleep pressure dissipates and goes down again to a level which means that your sleep homeostat is satisfied, you're ready to wake up again. It's a way of describing a biological need which in many ways is similar to hunger and thirst, for example.
Katie - Why might my biological clock be different to my partner's then?
Malcolm - Again, this is due to this biological variation that we have, to a significant part due to genetic differences. To put it simply, we have body clocks which tick a little bit faster or a little bit slower than other people's and, of course, then there's many of us who are somewhere in between. So, a fast body clock would make us what we call a morning type, or a lark, who naturally wakes up early and prefers to go to bed fairly early as well. And the opposite of that will then be somebody who has a slower body clock who is what we call a night owl, so this would be an individual who has a natural propensity to stay awake longer and to sleep in longer in the morning.
Katie - We've known about these body clocks and the differences for a while now, so what new research is coming out about the health consequences of not necessarily paying attention to those body clocks, because in modern life it can be actually quite difficult to find time to switch off or switch on, as it were, at the appropriate time of day?
Malcolm - Indeed. We know from a number of studies that sleep deprivation is not good for your physiology. Sleeping out of synchrony with your body clock is also not good for you, such as in jetlag or in shift work. But there's also a growing body of evidence that people who are night owls naturally have a bit of a raw deal in terms of health outcomes. So, there is a number of reports showing that, on average, night owls have a higher risk of having poorer mental health and poorer cardiovascular health, and also a higher risk of diabetes.
In a report that we published last year we used data from the UK biobank where middle-aged people when they signed up for this study, they answered a question about are you a morning type or an evening type on a scale with five steps. And what we found is that people who describe themselves as definite evening types, during these seven years they had a 10 percent higher risk of dying than the definite morning types. And it's really important to note that we have no reason to assume that there is something intrinsically unhealthy of being an evening type. What we think is happening is that evening types who are essentially forced to live in a world which is designed around the preferences of morning types, they have a difficult time because if you find it hard to fall asleep until quite late, but you still have to get up as early as everybody else, then you will start accumulating a sleep deprivation which, in the longer term, is detrimental to your health. And equally you can end up with something called social jetlag, which we often see in an evening type, and that means that in the weekend they essentially try to make up for having to sort of live against their natural inclination by almost sort of travelling to a different time zone by moving their activity patterns over the weekend and then back again on Monday, and that also is not good for the health.
Katie - How can we better accommodate these sleep differences then?
Malcolm - It is really important that we have an open dialogue about this in society and that we recognise that this natural biological variation is nothing to do with whether you are industrious or lazy or anything like that, it is just our biological background. Now there are, of course, some professions where there is no flexibility but in many professions it is possible to have flexible working hours, and fortunately people are now openly discussing flexible working hours for reasons such as care responsibilities. It should absolutely be an acceptable reason to ask for flexible working hours, if it is not detrimental to your availability for meetings etc., why would your employer not what you working during the eight hours when you are at your peak?
Katie - Now, napping is something we tend to associate with kids or babies. Is there any evidence to suggest the benefit of an adult nap, if your body clock doesn't necessarily complement the standard 9-to-5?
Malcolm - Well, if you need a nap then get it. It's not as good necessarily as getting the sleep at the appropriate time, but there's lots of evidence showing that even a short power nap actually can help us function better for the hours subsequent to that.