Your Brain On Caffeine
Our Western age places a great deal of stress on its work ethic. Growing tired is becoming increasingly unforgivable. This attitude, in part, has led to caffeine consumption skyrocketing over recent years. In the US alone last year, 26.7 million 60 kg bags of coffee were brewed and poured down the throats of the Motivated. If you add to this the energy drinks, pre-workout powders, and other sources of the stimulant that are now widely consumed, the picture you have is of the most extensively used psychoactive drug in the world.
If you've ever felt the sense of mental clarity and the intense high the right dose of caffeine can give you, this is hardly surprising. But have you ever wondered what systems inside of your body the caffeine molecule invades, or what it does inside them? This article is a short primer addressing these questions.
Dissolved inside of your drink, caffeine first enters your intestines. Depending on a host of factors - like your genetics, feelings, and diet - it will take 30-60 minutes for the concentration of the drug to peak in your bloodstream. Once all the caffeine is inside of you, your liver will eliminate half of the dose between 3 and 6 hours. If you smoke, this caffeine "half-life" is reduced, because of some compounds in cigarettes which make the liver work faster. It’s generally accepted that it takes 5 or so "half-life’s" for drugs to be removed from your body - which means that at best you’ll be completely clean of caffeine about 15 hours after ingesting your drink.
Because of its chemical structure, caffeine is a very versatile molecule. It can jump across every natural defense your body has, including the jealously protective barrier that lies between your blood vessels and brain. This property accounts for the speed with which you feel its stimulating mental effect. A little counterintuitive, perhaps, is the fact that this effect comes about by caffeine blocking, rather than stimulating, a normal brain function.
To better understand caffeine's activity, we'll have to talk a bit about energy. As you strain yourself mentally throughout the day, energy-dense chemical compounds scavenged by your body from the food you've eaten rush to active areas of the brain. Once there, the chemical structures of these compounds are altered, which releases the energy brain cells need. As this occurs, different chemical byproducts are released into the plasma that all brain cells bathe in. One of these byproducts, called adenosine, happens to be shaped very much like caffeine.
Almost every chemical that can influence the activity of your brain works by attaching itself to some ‘receptor’ protein that finds the shape of that chemical tolerably familiar. The brain is a vast nest peppered with myriads of different receptors, each of which has evolved to couple with a unique chemical. Once such a receptor-molecule union is attained, a small electrical response is generated. The interplay of such tiny electrical signals is the computational toolkit evolution has gifted the brain.
Due to their similar shapes, adenosine and caffeine can slide into the same receptor - known as the adenosine receptor (AR). In fact, there are a few AR receptor ‘sub-types’, all of which are subtly different but can nonetheless recognize the shape of both adenosine and caffeine. Each AR subtype is present in a different part of the body, and each can contribute to a different bodily function. This wide reach of the adenosine molecule explains the mild side-effects of caffeine consumption, like the fact that it makes a person produce more urine or feel less pain.
The chief AR sub-type which caffeine preys on is called the A1R. Hosts of it dot an area deep inside of the brain called the basal forebrain. Part of this area is formed by a neural circuit which stimulates wakefulness. This circuit crackles away all day, keeping you awake. Because you’re awake, however, adenosine concentration inside your brain rises. When an adenosine molecule happens to connect to an A1R of the basal forebrain, a key excitatory component of the wakefulness circuit receives a tiny shock of electrical inhibition. The circuit is gradually silenced by an onslaught of tiny shocks, and the brain drifts off to sleep.
If present inside your brain, caffeine impedes this natural process. It sneaks inside the A1R and blocks the region of the receptor which is sensitive to adenosine. This allows your wakefulness circuit to keep plugging away undisturbed despite the many adenosine molecules floating around it. This process underlies the energy ‘boost’ caffeinated drinks provide.
Though it works well for a while, caffeine is ultimately removed – the body perceives it as a toxin, after all – and the large levels of adenosine that have built up take over. If you allow this to happen chronically, by drinking a cup or two of coffee every day, several things happen. Firstly, more A1R receptors are created and inserted inside of your basal forebrain. Secondly, these receptors develop a resistance to caffeine, latching onto it less easily and producing weaker electrical signals when they do. Put together, you develop a ‘tolerance’ and must ingest larger quantities of caffeine to experience the same subjective feelings.
Although this process effectively describes an intervention into the natural sleep cycle, and that might sound rather glum, it’s been conclusively shown that having caffeine in your brain constantly is neuroprotective. This means a person is less likely to develop some of the terrible cognitive diseases associated with age, like Alzheimer’s disease. It doesn’t mean that caffeine is always a good idea, however. Keeping in mind the mechanism by which it functions may help you better manage your use and get more out of an immensely popular substance.
References
Porkka-Heiskanen, T. & Kalinchuk, A. V. Adenosine, energy metabolism and sleep homeostasis. Sleep Medicine Reviews 15, 123–135 (2011).
Nehlig, A., Daval, J.-L. & Debry, G. Caffeine and the central nervous system: Mechanisms of action, biochemical, metabolic and psychostimulant effects. Brain Research Reviews 17, 139–170 (1992).
Fiani, B. et al. The neurophysiology of caffeine as a central nervous system stimulant and the resultant effects on cognitive function. Cureus (2021). doi:10.7759/cureus.15032