"Caffeine interferes with the normal dance of neurotransmitters that control sleep by blocking the receptors for adenosine..." #readingToday
Caffeine interferes with the normal dance of neurotransmitters that control sleep by blocking the receptors for adenosine, a by-product of energy use that accumulates during our daily exertions. Adenosine makes us feel tired, but if the receptors it binds to are clogged up by caffeine, it can't have this effect—which is why you feel so alert after that early morning cappuccino. Of course, you can also become tolerant to caffeine if you consistently have a lot of it, but no matter how tolerant you are, it still stays in your system for up to ten hours and causes your sleep to be significantly lighter. If you think your five daily espressos are having no impact at all, just try going without them for a week. The built-up dependence will probably lead your body to protest with skull-splitting headaches and cravings for coffee. It is probably best to resist these if you really care about your sleep!
(Moon+ Reader Pro v2.3.3, The Secret World of Sleep: The Surprising Science of the Mind at Rest (MacSci))