How coffee can wreck your sleep

Coffee lovers beware: drinking it at night disrupts your body clock by almost an hour, leading to less sleep...
21 September 2015

Interview with 

Dr John O’Neill, MRC Laboratory for Molecular Biology


A lovely cup of coffee


Coffee lovers take note! Researchers have discovered how much of a boost Coffeecaffeine gives us, and drinking it at night may affect you more than you might think. As little as a double espresso three hours before bed can delay your internal body clock by forty minutes, but we could use this to fight jet lag. Graihagh Jackson went for a cuppa with study author John O'Neill...

John - Sleep is regulated by two processes. One of them is a homeostatic drive. The longer you've been without sleep, the more you need to sleep. But the other part of when we sleep is the circadian rhythm and the circadian rhythm controls when we're most likely to go to sleep. And so, the first aspects of how caffeine works has been studied quite intensively over the last few decades. But no one had really addressed the extent to which the body clock is affected by caffeine. And so, that's what we looked at.

Graihagh - And how did you go about looking at that?

John - Over in the states, at the University of Colorado in Boulder, my colleague, Ken Wright took several individuals and placed them in constant conditions for 49 days. What he did was give them either a placebo pill or caffeine and then look at how the melatonin rhythm was affected by caffeine. Now, just to tell you about melatonin, it's the main hormone of night. It makes you feel sleepy. What Ken observed was that in response to a caffeine pill equivalent to a double espresso at 3 hours before their normal bedtime, that surge in melatonin is delayed by nearly an hour.

Graihagh - What's the effect of that then? Do you just go to sleep an hour later?

John - Effectively yes and the consequence of that is that left to your own devices, you would sleep an hour later. But of course, most people would have to get up for work and so, the real consequence is that you just simply get less sleep.

Graihagh - So, this is in the group studies in people but you in your lab, you've looked at this at the cellular level.

John - That's absolutely right. So, the really fascinating thing for me is that this biological rhythm in humans is something that's present in every single cell of the body. And so, I could take a scraping of your skin cells and grow them in a petri dish and they would continue to have this 24-hour rhythm. And so, that really gave us a handle to get at the mechanism of what's going on in a person when they take caffeine or when they drink a coffee. Because of course, all of these same target proteins that are bound by caffeine, things like adenosine receptors and phosphodiesterases, all of those are present in pretty much every human cell type. It allows us to really pharmacologically dissect the mode of action of caffeine upon the cellular circadian rhythm.

Graihagh - And this mechanism that you're talking about, the proteins binding with the caffeine, that wasn't known before?

John - So, in the context of sleep and arousal, it's been accepted in the sleep field for quite a long time. But the thing that had not been considered previously really was that caffeine affects the circadian clock in cells, again, through adenosine receptors. So, we could rule out all of the other suggested targets of caffeine.

Graihagh - As a frequent coffee drinker myself, what sort of message should I be taking away from this, that I shouldn't be drinking coffee after 3 pm?

John - I think it depends on your natural - what we call, chronotype. So, your chronotype is your innate tendency to get up at a particular time. And so, there's some wonderful research done by (Tole Rhomberg and Russell Foster) showing that as we age, going from toddlers, through to our late teens and early 20s, we naturally get later and later, and later but then after that, we get earlier and earlier, and earlier again so that a toddler and someone in their 70s is naturally waking up very, very early.

Graihagh - So, you should have kids when your 70. Does that work?

John - Or you should have grandparents, yeah. But within that, there is obviously an enormous variation. And so, something that is potentially useful is that if you know you're a lark and yet, you have to do a job that involves you behaving more like an owl, it might be useful to you to take caffeine at an intelligent time to actually delay your circadian clock by just enough that you can get up a little bit later and stay up that bit later. To do so, so as to avoid the loss of sleep because of course we know that not getting enough sleep associates very strongly with obesity, some metabolic disorders, cardiovascular disease. And so, that's something that you really want to watch out for. But certainly, if you're naturally a lark and you want to stay up later then the intelligent use of caffeine might be able to help with that.


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