We all know the usual effects of caffeine, to a greater or lesser extent: increased alertness, decreased fatigue, shaky hands, mild anxiety and, of course, an urgent need to go to the toilet. Caffeine withdrawal is characterized by severe headaches, fatigue and difficulty in focusing in the DSM-5 Diagnostic Criteria Reference Manual, the holy book of psychiatry. In fact, caffeine is the most widely used psychoactive drug in the world.
Caffeine tricks and manipulates the adenosine receptors in your brain. You've probably heard that adenosine is one of the four nucleosides that make up your DNA, or the substrate of ATP (adenosine triphosphate), the energy currency of cells. What you may not have heard is that this multi-purpose molecule is also a neurotransmitter and a regulator of vasodilation, the widening of your blood vessels. During the day, adenosine slowly accumulates in postsynaptic areas and activates sleep-promoting receptors. Just like a naughty child putting play dough into a keyhole, caffeine binds to adenosine receptors but does not activate them. This prevents adenosine from promoting sleep. In summary, caffeine is similar enough to adenosine that it binds to the same receptors as it, but is too different to actually activate those receptors. This results in the tremendous alertness and energy that coffee lovers feel.
Who among us hasn't experienced the sweet bliss of a much-needed espresso in the afternoon? But still, if you push your luck too much, you may wake up one morning with a throbbing headache. Since adenosine regulates vasodilation, blocking adenosine receptors will cause blood vessels to narrow. When this effect of caffeine wears off, the rush of blood to the newly expanded veins can sometimes be painful. Moreover, neurons will add new adenosine receptors to synapses to compensate for the caffeine blockade, resulting in daytime sleepiness and increased caffeine needs. Western culture often exalts the view that sleep is laborious at best and lazy at worst. Whether you're a professional achievement hunter or a weekend warrior, If you live by the "I'll sleep when I'm dead" motto, it's easy to get caught in a vicious caffeine cycle where you need more and more to ward off the sleep fairy. So why is the coffee you drink in the afternoon dangerous when you don't sleep hours later? According to some data, 80% of plasma caffeine levels are present in your brain, and the half-life of caffeine is 3-7 hours, meaning your blood caffeine levels only halve every few hours. Considering caffeine's role in staying alert, a morning cup of coffee is extremely tempting. When used in the right amount and at the right time coffee can be a satisfying and productivity-boosting part of your morning routine. Just be careful when tempted for a coffee in the afternoon!