Is your sleep account overdrawn?

05 February 2016

Interview with 

Dr John O’Neill, MRC Laboratory for Molecular Biology


Drinking moderate amounts of caffeine could be good for you but what about sleepingwhen you drink it? If you drink it late at night, how does this affect our sleep and could it have detrimental long term effects? Dr John O'Neill from MRC Laboratory for Molecular Biology spoke to Chris Smith about the possible affects...

John - Whether or not we sleep is dependent upon two separate, though related, biological processes.  One of them is your homeostatic sleep drive and that is something that simply accumulates the longer that you have been awake.  And that's very much dependent on adenosine and adenosine receptors that have already been mentioned and, in that context, the longer you have been awake the more adenosine you have in the brain and, in that context, adenosine acts like a sedative...

Chris - So it's trying to make you go to sleep?

John - Exactly, and so...

Chris - That's why the longer you have been awake, the more sleep you get because it's just building up?

John - That's exactly right. But then there is another equally important process - your circadian rhythm and that's the internal, biological clock that regulates so many different aspects of our physiology; such as, when we feel hungry but also when we fall asleep and when we wake up in the morning.

Chris - There is literally a neurological clock ticking away in the brain that's keeping time and it gets us up in a morning and send us to bed at night?

John - It's even more interesting than that.  Not only is it in the brain but it's in every single cell in the body.  So I could take a scraping of your skin cells, grow them in a petri dish and they would still have an approximately 24 hour rhythm and when various clock genes are turned on and off.

Chris - So my body knows what time of day it is and metabolically it's gearing up for when I'm going to get up in a morning, it's winding me down at night.  You've answered the question - what does caffeine do to the buildup of adenosine in the brain that's trying to inextricably build up and send me to sleep anyway, but what about the circadian clock?  What does caffeine do to that then?

John - That's a question that had not actually been answered until recently.  So, in collaboration with a colleague in the States, Ken Wright at the University of Colorado; in the first experiment we took five humans and persuaded them to spend 49 days in constant dim lights basically - not a huge amount of fun.  But, under those very well controlled experimental conditions, we could monitor their biological clock by looking at the timing of the release of the sleep hormone melatonin.  And so then what we do is give them, three hours before their normal bedtime, either a placebo pill or a caffeine pill.  And the caffeine pill is about 200 mgs - about the same you'd get in a double espresso...

Chris - Nice strong coffee...

John - Exactly.  And what we observed was that the melatonin increase was delayed by nearly an hour.  Okay, so what you're basically doing is the equivalent of jetlagging yourself.

Chris - In other words, taking that dose of coffee at whatever time of day, is going to push back the natural time when you say -  when your brain is normally going to tell you go to sleep and so you're going to start to wind down an hour later than you otherwise would, or so?

John - We actually can't say that yet.  All that we can say confidently at the moment is that taken in the evening it will delay your biological clock, and then, the fascinating thing is that we can see exactly the same thing at the cellular level.  So in human cells, treating them with caffeine has the same effect - it delays the biological clock.  So the thing that's important in terms of your health - taking a step back -  is that we know that circadian disruption as occurs during shift work, for example, is really bad for you in the long term.  So there's a very strong association with chronic diseases such as diabetes, neurodegenerative disorders...

Chris - Breast cancer...

John - Exactly, yes.  A load of different cancers.

Chris - So, don't tell me that by taking coffee into the evening, I might be pushing myself into almost the same regime and increasing my disease risk?

John - It's unlikely that it's going to be of the same magnitude of the risk associated with shift work but it's certainly likely to be pushing you in that direction.

Chris - Am I robbing myself of sleep though, John, in the sense that if I do this and I enable myself to stay active for longer into the evening but then I still set my alarm clock for 7oclock the next morning, am I effectively building up a sleep debt this way?

John - Yes.  You are building up a sleep debt and, not only that, going back to the homeostatic sleep drive, if you put one of these electroencephalograms on an individual during sleep...

Chris - Measures brain waves?

John -   Exactly right - measures brain waves.  You see that the delta power, these slow waves that are very characteristic hallmarks of deep sleep, are much more disrupted in individuals that have had caffeine.  So, not only are you going to increase your sleep debt by drinking coffee late at night, or any form of caffeine late at night, but also the quality of the sleep is going to be less.

Chris - Because the normal pattern of sleep that evolves over a night is not going to be fulfilled in your average night.  So would your advice then, on the basis of what you're finding, that perhaps people shouldn't push their coffee drinking into the late night?

John - Clearly it is going to vary between individuals, as Thomas said.  So some people just do not notice a coffee in the evening and that's got to be due to genetic variation...

Chris - And I'm one of them.  I will drink coffee until the cows come home and it doesn't seem to affect my sleep.

John - So that's got to be due to genetic variation within the population...

Chris - Or just saturation?

John - No, no, no!  It can't be due to saturation because this aspect, you don't seem to be able to tolerate to  its effects upon sleep and the circadian rhythms.  So what I would probably advise, based on what we know at the moment, that in caffeine sensitive individuals, they really should try not to drink caffeine at night.


Add a comment