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Obviously caffeine is a stimulant, and wakes us up.

Is there any research into how it affects fatigue: e.g. how different it is to rest (i.e. I'm not asking about the pathways by which caffeine achieves this).

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closed as unclear what you're asking by AliceD, Robin Kramer, honi, huh, Seanny123 Jun 27 '16 at 22:21

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ What exactly are you asking? $\endgroup$ – TheEnvironmentalist Jun 13 '16 at 18:10
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    $\begingroup$ I think maybe the OP is looking for research that compares the effect of say, an hour of sleep to a cup of coffee on fatigue (eg, ratings, or cognitive performance) to see if they are equivalent (ie, is it safe to sleep less and drink coffee instead). $\endgroup$ – Arnon Weinberg Jun 13 '16 at 21:35
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    $\begingroup$ @ArnonWeinberg - makes sense, but having to guess the question's scope warrants closure imo. $\endgroup$ – AliceD Jun 13 '16 at 22:31
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    $\begingroup$ i'm honestly baffled why this seems to have confused so many of you. i'm not looking for quantitative measures of coffee and sleep, but the differences in how each changes cognition $\endgroup$ – user3293056 Jun 14 '16 at 4:53
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    $\begingroup$ Notice how in answering your question, I rephrased it as my interpretation, Can caffeine replace sleep, and then added in some background and miscellaneous information as needed to form a complete answer. I basically took a shot in the dark as for what I was answering. If you put your question in the form of a simple, concrete sentence with a question mark at the end, it would be far easier to answer, and you would probably have a few more answers. $\endgroup$ – TheEnvironmentalist Jun 16 '16 at 15:29
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Can caffeine replace sleep? The simple answer here is no. The easiest way to explain why is to dip our toes into the mechanism by which caffeine works.

In a nutshell, a large part of what you perceive as drowsiness is caused by adenosine building up in adenosine receptors. The longer you stay awake (and the more active you are to a degree), the more adenosine builds up, the more drowsy you get, until finally you sleep and the adenosine is flushed out. Caffeine is a competitive antagonist of adenosine receptors, meaning that it fights adenosine for spots in the receptors and blocks adenosine from activating the receptor, without the caffeine itself activating them. The longer you stay awake on caffeine, the more adenosine fights caffeine for spots in the receptors, and the more other signs of sleep deprivation that aren't affected by caffeine accumulate. This is why you might sometimes experience that odd "worn out but not exactly tired" feeling late into an all-nighter. Caffeine doesn't actually provide rest or any equivalent, it basically creates the illusion of being well-rested, even as you continue to build sleep debt.

Caffeine doesn't seem to be able to replace sleep, simply delay it, and you can easily test this yourself. Also, as your body breaks down caffeine over a number of hours, and the impact of sleep deprivation increases the longer you force yourself to stay awake, you will need to continue to consume more and more caffeine to maintain the effect.


Sources:

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