caffeine binds to these [adenosine] receptors, blocking the adenosine from binding and hence reducing the feeling of tiredness
Caffeine, whether it be through an espresso, Diet Coke, matcha or even pills, is probably the most consumed drug by students (well, perhaps with the occasional exception of alcohol…). No matter what you study or where you work, chances are you will be relying on this psychoactive drug to wake you up and improve alertness, throughout at least some parts of your life. And if you don’t, you’re in the minority: the FDA stated that ~80% of adults in the US ingest caffeine daily. The basic effects of increased concentration and faster heartbeat are commonly known – but do you really know what goes on from a biological/chemical viewpoint?
While caffeine provides no nutritional value, it does exert a profound effect on your body. The most desired effects occur as a result of it acting as a stimulant on the central nervous system, thus decreasing fatigue and increasing alertness and good mood, typically for up to 4-5 hours. During a normal day, a chemical called adenosine builds up in your body and activates adenosine receptors, explaining the onset of drowsiness as the day progresses. Caffeine, meanwhile, binds to these receptors, blocking the adenosine from binding and hence reducing the feeling of tiredness. The effects of other natural stimulants, such as dopamine and glutamine, are then felt more, resulting in a mood-boosting effect. The blockage of adenosine receptors also explains the rapid crash caused by caffeine after a few hours; during the time caffeine is bound, adenosine continues building up – you just don’t feel its effects, as it is not bound to the receptors. The dissociation of caffeine from the receptors suddenly frees up a lot of space, and all the accumulated adenosine is able to bind. Therefore, rather than gradual adenosine binding over time, you experience a sudden increase when the caffeine wears off.
One study even found that caffeine was linked to a 45% lower suicide rate!
Apart from cognitive improvements, caffeine can also improve athletic performance, by increasing heartbeat and delaying the onset of muscle fatigue. On a cellular level, this is achieved by caffeine’s blocking of phosphodiesterase (PDE). PDE is an enzyme which usually breaks down cAMP, a chemical messenger affecting various reactions, and thus inhibiting PDE prolongs and intensifies the effects of cAMP. In the heart, this promotes norepinephrine and epinephrine (adrenaline) release, increasing heart rate, force, and blood pressure, and delivering more oxygen to the muscles.
There are also other, less-known long-term benefits: studies show that drinking coffee regularly may result in lower risks of developing Alzheimer’s disease, Parkinson’s disease, oral cancer, or even suicides (one study found that caffeine was linked to a 45% lower suicide rate!).
However, due to an increase in adrenaline and inhibition of artery-diluting chemicals, caffeine also increases blood pressure in the short-term. Moreover, due to its acidic nature, caffeine increases the production of stomach acid and may cause heartburn or acid reflux. Since it doesn’t get absorbed by the body, it is excreted through urine (explaining why you are prone to urination shortly after consumption). And the effects are not only physical: ever felt that drinking coffee can make you more stressed, rather than energised? This is also scientifically backed - if you are prone to anxiety or sleep issues, or even just experiencing short-term stress, caffeine may exacerbate the effects of them through increased adrenaline production.
Excessive consumption may lead to female fertility issues, or foetal developmental issues in women who are already pregnant. Furthermore, caffeine prevents calcium absorption in the bones, increasing the risk of osteoporosis with age. In extreme cases, a caffeine overdose can result in convulsions and death, most commonly through overconsumption of energy drinks or pills (in which you are typically not as aware of the amount of caffeine present, as you would likely be with coffee or tea). But don’t worry - staying below the recommended limit of 400mg/day, or around 4 cups of brewed coffee or 10 cans of coke is totally fine, and the amount needed to result in the gravest effects is over 1g.
Over time, just like with any other drug, ingesting too much caffeine can increase your tolerance to its effects, for example by creation of new adenosine receptors (and so you need more caffeine molecules to block them). Subsequent reduction of intake can cause withdrawal symptoms - in particular headaches, fatigue, irritability and even tremors. Therefore, if you’re trying to decrease your intake, make sure to do so slowly, or perhaps by switching to alternatives with a slower caffeine release mechanism, such as matcha instead of coffee. The extent to which caffeine affects you, however, is not only based on tolerance, but also genetics, age, body mass and other factors, so it is important to observe the effects it has on your body and not compare your reaction to that of others.
Overall, while caffeine may have some unpleasant effects, especially if you’re prone to indigestion, anxiety or heart conditions, it is generally considered as a non-harmful, and even health-boosting stimulant, so go order that Nespresso machine you’ve been eyeing (or, for a more budget-friendly alternative, get yourself a free Pret subscription) – it’s worth it.