Van Geijlswijk makes the important point that if you take 0.3 mg seven hours before bedtime, none of it is going to be remaining in your system at bedtime, so it’s unclear how this even works. But – well, it is pretty unclear how this works. In particular, I don’t think there’s a great well-understood physiological explanation for how taking melatonin early in the day shifts your circadian rhythm seven hours later.
It seems to me there’s a very obvious model for this: the body clock is a chemical clock whose current state is stored in the concentration/configuration of various chemicals in various places. The clock, like all physical systems, is temporally local. There seems to be evidence that it keeps time even in the complete absence of external cues, so most of the “what time is it” state must be encoded in the body (rather than, e.g., using the intensity of sunlight as the primary signal to set the current time). Taking melatonin seems like it’s futzing directly with the state of the body clock. If high melatonin encodes the state “middle of the night”, then whenever you take it should effectively set your clock to “it’s now the middle of the night”. I think this is why it makes it possible to fall asleep. I think that it’s then the effects of sunlight and actually sleeping and waking up that drag your body clock later again (I also have the effect that at anything over 0.1mg or so, I’ll wake up 5h45m later, and if my dose is much more than 0.3mg, I won’t be able to fall back asleep).
I’m pretty confused what taking it 9h after waking does in this model, though; 5--6 hours later, when the “most awake” time happens in this model, is just about an hour before you want to go to bed. One plausible explanation here is that this is somehow tied to the “reset” effect you mentioned from staying up for more than 24 hours; if what really matters here is that you were awake for the entirety of your normal sleep time (or something like that), then this would predict that having melatonin any time between when you woke up and 7 hours before when you went to sleep would have the “reset” effect. An alternative (or additional) plausible explanation is that this is tied to “oversleeping” (which in this model would be about confusing your body clock enough that it thinks you’re supposed to keep sleeping past when you eventually wake up). If the body clock is sensitive to going back to sleep shortly after waking up (and my experience says this is the case, though I’m not sure what exactly the window is), then taking melatonin 5--6 hours before bed should induce something akin to the “oversleeping” effect (where you wake up, are fine, go back to sleep, sleep much more than 8 hours total, and then feel groggy when you eventually get up).
The normal tendency to wake up feeling refreshed and alert gets exaggerated into a sudden irresistable jolt of awakeness.
I’m pretty sure this is wrong. I’ll wake up feeling unable to go back to sleep, but not feeling well-rested and refreshed. I imagine it’s closer to a caffeine headache? (I feel tired and headachy but not groggy.) So, at least for me, this is a body clock thing, and not a transient effect.
It seems to me there’s a very obvious model for this: the body clock is a chemical clock whose current state is stored in the concentration/configuration of various chemicals in various places. The clock, like all physical systems, is temporally local. There seems to be evidence that it keeps time even in the complete absence of external cues, so most of the “what time is it” state must be encoded in the body (rather than, e.g., using the intensity of sunlight as the primary signal to set the current time). Taking melatonin seems like it’s futzing directly with the state of the body clock. If high melatonin encodes the state “middle of the night”, then whenever you take it should effectively set your clock to “it’s now the middle of the night”. I think this is why it makes it possible to fall asleep. I think that it’s then the effects of sunlight and actually sleeping and waking up that drag your body clock later again (I also have the effect that at anything over 0.1mg or so, I’ll wake up 5h45m later, and if my dose is much more than 0.3mg, I won’t be able to fall back asleep).
I’m pretty confused what taking it 9h after waking does in this model, though; 5--6 hours later, when the “most awake” time happens in this model, is just about an hour before you want to go to bed. One plausible explanation here is that this is somehow tied to the “reset” effect you mentioned from staying up for more than 24 hours; if what really matters here is that you were awake for the entirety of your normal sleep time (or something like that), then this would predict that having melatonin any time between when you woke up and 7 hours before when you went to sleep would have the “reset” effect. An alternative (or additional) plausible explanation is that this is tied to “oversleeping” (which in this model would be about confusing your body clock enough that it thinks you’re supposed to keep sleeping past when you eventually wake up). If the body clock is sensitive to going back to sleep shortly after waking up (and my experience says this is the case, though I’m not sure what exactly the window is), then taking melatonin 5--6 hours before bed should induce something akin to the “oversleeping” effect (where you wake up, are fine, go back to sleep, sleep much more than 8 hours total, and then feel groggy when you eventually get up).
By the way,
I’m pretty sure this is wrong. I’ll wake up feeling unable to go back to sleep, but not feeling well-rested and refreshed. I imagine it’s closer to a caffeine headache? (I feel tired and headachy but not groggy.) So, at least for me, this is a body clock thing, and not a transient effect.