Here is an interesting study done by some folks at the University of Mainz in Germany.
The article is titled:
“Effects of caffeine intake on the pharmacokinetics of melatonin, a probe drug for CYP1A2 activity”
and can be found at:
Among other things, it states that, “caffeine was found to increase the oral bioavailability of melatonin”.
That makes sense I suppose. As far as I know, caffeine works by inhibiting adenosine, which is itself a type of “inhibitor”. So maybe adenosine or something
like it is also inhibiting melatonin? Hmmm…
That being said, the focus of this study was on the “oral bioavailability” of melatonin. Which, I assume, is talking about melatonin supplements. However, maybe caffeine has some effect on endogenous melatonin as well? I’m speculating here, and I’m way out of my field of knowledge, (liberal arts degree be damned) but hey why not?
At any rate, if indeed caffeine has an effect on increasing endogenous melatonin, (my probably, easy- to-prove-against-speculation) this would be quite the news. It would certainly give credence to all those miraculous individuals who are able to have a cup of coffee and then promptly fall asleep. It would also seem, that the key to utilizing caffeine for wakefulness is to use it with light!
On the other hand…if one is a regular coffee/caffeine user,
and would consequently have higher levels of adenosine,
then perhaps the higher adenosine levels would suppress melatonin and give the user a difficult time while trying to fall asleep. This might especially be the case if one only had caffeine early in the day.
For example, lets say coffee is gulped down in the morning, thereby suppressing adenosine levels. With its natural penchant for homeostasis, the body would respond by creating higher levels of adenosine. Over the course of the day, the caffeine will fade away and the adenosine will slowly creep back into place. Only by now, it is at much higher levels. By the time night comes, the higher levels of adenosine will be suppressing everything from adrenaline to melatonin. Thereby making the user both incredibly exhausted, yet somewhat of an insomniac. Which in turn probably leads to terrible sleep, a groggy morning and another cup of coffee.
But! If you had been taking coffee all day and keeping your adenosine levels low, then perhaps your melatonin levels might be at their normal proportions by bedtime. However, I’m not really sure of the speed at which all this is happening. Perhaps adenosine launches back at full strength far faster than I’m accounting for. In addition, if you were drinking caffeine all day you would have to deal with the other effects of adenosine suppression…namely higher levels of adrenaline!
Good grief, to think there is so much going on “under the hood” when you drink coffee and try to go to sleep. ☺