When do you feel sleepy

Alice Hello and welcome to 6 Minute English. I'm Alice… Neil And I'm Neil. And I feel terrible! Alice You look terrible, Neil – if you don't mind me saying so! Neil It's because I had to get up really early this morning. Alice Oh dear! What time did you have to get up? Neil Eight o'clock. Alice Oh, Neil! That isn't early! I get up at six every day. It's so peaceful early in the morning. Neil Hmm. Well, some people are morning people and others… aren't! Alice Yes. Well, today we're talking about the biological reason for this – it's all about circadian rhythms. They are produced by a so-called body clock in our brains that regulates our body functions: our body temperature, sleepiness and alertness, hunger, and hormone levels. Plants, animals, and many microbes have circadian rhythms. Neil You know a lot about circadian rhythms. Alice And I'll ask you a question related to them. What does the word 'circadian' mean? Is it… 6 Minute English © British Broadcasting Corporation 2016 bbclearningenglish.com Page 2 of 5 a) around a day? b) every day? or c) twice a day? Neil Hmm. I'm going to say a) around a day. Alice Well, we'll find out whether you got the answer right or not later on in the show. Now let's talk about circadian rhythms and our internal clock. Neil Why do our bodies need an internal clock to tell us where we are in the day? Isn't it obvious? Alice No, it isn't – take jet lag, for example. We rely on the predictable cycle of light or dark in a 24-hour period to synchronise – or adjust – our body clocks to the environment – and if we mess about with the light and dark cycle by flying into a new time zone, it makes us feel really bad! Neil Good point – jet lag is the disruption of our circadian rhythms caused by high-speed travel across different time zones, which can cause tiredness and sleep problems. But Alice, if we rely on day turning to night to adjust our body clocks, what happens to blind people? – Because I assume their body clocks can't do this. Alice Blind people who have some light perception are able to synchronise their circadian rhythms to the light-dark cycle. But those who have no light perception at all… well, let's listen now to Debra Skene, Professor of Neuroendocrinology at the University of Surrey. She can explain what happens. INSERT Debra Skene, Professor of Neuroendocrinology at the University of Surrey Totally blind people – they've lost that connection between the light-dark circle and the clock. So there isn't anything wrong with the clock but the clock ticks and oscillates at its own endogenous period just the same as if I were to put you in a dark cave. Your biological internal clock would oscillate at your endogenous circadian period. Neil So if you're totally blind – or able to see but living in a dark cave – you have a ticking clock but with no connection to the outside world. The clock oscillates at its own endogenous, or internal, period. 6 Minute English © British Broadcasting Corporation 2016 bbclearningenglish.com Page 3 of 5 Alice Oscillate means to move back and forth in a regular rhythm – like the pendulum on a clock. Neil Do you think my endogenous clock ticks faster than yours, Alice? Alice It isn't a competition, Neil. And actually, mine probably ticks faster than yours since I'm a morning person. Anyway, the normal range in humans is between 23.8 to 24.8 hours. And this is also true for totally blind people. Neil But their clocks are free-running – they don't get cues from the outside environment telling them when to wake up, when to eat, when to feel sleepy. So that means they might feel sleepy at the wrong time of day – for example, when they're at work. Or alert in the middle of the night when they should be asleep. Alice It's worth talking about people who do shift work too – which means work that takes place outside the traditional 9 to 5 day. Neil Shift workers may suffer similar problems to blind people because they are trying to sleep against the clock. They might sleep in the day and work at night for example – which goes against the light-dark pattern. Alice There are some long-term health problems associated with shift work – certain cancers, heart disease, and obesity. Neil So what can people do to help adapt their circadian rhythms to a night shift schedule? Alice Well, let's hear what Professor Debra Skene has to say about it. INSERT Debra Skene, Professor of Neuroendocrinology at the University of Surrey We do think that exercise and food, caffeine, may be able to modulate in some way, so has some influence on circadian timing, but not as strongly as the light-dark cycle. Neil 6 Minute English © British Broadcasting Corporation 2016 bbclearningenglish.com Page 4 of 5 So the strongest influence over our circadian rhythm is the light-dark cycle. We can't alter night and day, after all! Alice Debra Skene says that other cues such as food and exercise will modulate – or adjust – the body clock. So eating three well-balanced meals at regular times each day can help your body clock adapt to an unusual schedule. Neil Taking naps – or short sleeps – just before you start a night shift can help you feel more alert. And keeping to the same sleep schedule every day will also help. Alice And don't forget caffeine – my old friend! A cup of coffee works wonders for me in the morning. Now remember I asked: What does 'circadian' mean? Is it… a) around a day, b) every day or c) twice a day? Neil And I said around a day. Alice And you were… right! Well done, Neil. The term 'circadian' comes from the Latin circa, meaning 'around' (or 'approximately'), and diēm, meaning 'day'. Now, let's hear the words we learned today. Neil They are: circadian rhythms synchronise jet lag oscillate endogenous shift work modulate naps Alice That's the end of today's 6 Minute English. Don't forget to join us again soon! Both Bye!