Be it an emotional support latte, a calming brew, an emergency Red Bull, or exam-season ProPlus (you freaks), most of us have dabbled in caffeine use at one time or another. Whatever your poison, you’d probably be hard-pressed to find a Cambridge student who isn’t partial to (or, more likely, dependent upon) a regular dose of caffeine. Yet, we sip our cold brew without understanding what this powerful drug is actually doing to our bodies. Caffeine wakes us up, but it also affects our heart, physical performance, mood and sleep. It’s shaped culture, started wars and revolutions, and fuelled some of the greatest thinkers of history. So, how does caffeine work? Could it be dangerous, or is that flat white actually improving your grades?

Caffeine, or to use its systematic name, 1,3,7-trimethylxanthine, is produced by more than 60 plant species, from coffee and tea to some species of citrus and holly. This probably evolved as a defence mechanism against herbivory, as its bitter taste discourages insects from eating these plants. This strategy doesn’t seem to have worked on humans, though - it’s estimated that 85-90% of people in Europe and North America consume at least one caffeinated beverage per day, making it the most widely used psychoactive drug on the planet.

“it’s estimated that 85-90% of people in Europe and North America consume at least one caffeinated beverage per day, making it the most widely used psychoactive drug on the planet”

Understanding how caffeine works requires some background on how our cells use energy. Adenosine triphosphate, or ATP, is a molecule produced by mitochondria (yes, the powerhouse of the cell), and is used as a kind of energy currency. As ATP is ‘spent’ in powering chemical reactions, it is broken down, producing a smaller molecule called adenosine. The build-up of adenosine that occurs as our cells use ATP throughout the day is detected by adenosine receptors in the brain, making us feel tired. Caffeine has a similar structure to adenosine, and so can bind to and block these receptors, preventing them from sensing this increase in adenosine and making us feel more alert.

The effects of caffeine on cognition (it’s been shown to improve attention, reaction time and working memory) have been recognised by great thinkers for centuries. Voltaire is rumoured to have drunk upwards of 40 cups of coffee per day (although it’s likely this was weaker than what’s on offer in Pret today), with Isaac Newton and Kant also having been fans. In true absurdist fashion, Kierkegaard is reported to have filled his cup to the brim with sugar, which he then dissolved with strong black coffee to fuel his work late into the night.

“Voltaire is rumoured to have drunk upwards of 40 cups of coffee per day (although it’s likely this was weaker than what’s on offer in Pret today)”

The brain-boosting effects of caffeine may have shaped history. Although the popular notion that everyone in the Middle Ages exclusively drank beer instead of water is probably a myth, ales were certainly the most popular alternative beverage for most of Europe. Farm workers took ‘beer breaks’, ‘ship’s beer’ was taken instead of water on long voyages, and alcoholic drinks were drunk from breakfast onwards, including by children. So, it’s probably not a stretch to say that, until the mid-16th century, a large part of society was probably at least tipsy for most of the day.

The switch from drinking alcoholic drinks to drinking coffee and tea that began to occur as these products were introduced to Western societies is theorised to be at least partly responsible for the explosion of innovation that occurred over the following centuries (think the Scientific and Industrial Revolutions, and the Enlightenment). Coffeehouses, nicknamed ‘penny universities’, became cultural fora, where people would gather to discuss philosophy or politics, or listen to music or poetry. In London, a coffeehouse dedicated to selling stock eventually became the London Stock Exchange; in the US, the Boston Tea Party was planned at a coffeehouse called the Green Dragon. As well as just facilitating congregation, it’s very likely that the collective cognitive boost offered by the presence of caffeine played a role - it’s a different sort of conversation you have over a latte than over a pint. In fact, Europe came late to the (tea) party: the widespread use of caffeine has been credited with a similar role in kickstarting the Chinese and Islamic golden ages.

“the widespread use of caffeine has been credited with kickstarting the Chinese and Islamic golden ages”

As well as increasing alertness, caffeine has other cognitive effects. Adenosine regulates the release of many neurotransmitters in the brain, including serotonin and dopamine, meaning caffeine can block this action to alter your mood. Together with the increase in heart rate caused by blocking adenosine receptors in the heart, this means caffeine, especially at high doses, can increase anxiety. Just like alcohol, caffeine is absorbed more quickly on an empty stomach, which is why you might get more jittery from a cup of coffee before breakfast.

The build-up of adenosine that occurs throughout the day is also referred to as sleep pressure, as it increases the activity of sleep-promoting regions of the brain. Blocking this effect means caffeine increases your sleep latency (the time it takes to fall asleep), as well as decreasing the quality of your sleep. It could be having an effect for longer than you think, as well. The half-life of caffeine in most people is around 5-7 hours, meaning if you drink a coffee at 5pm, half that caffeine could still be in your system when you’re trying to fall asleep at 11. There is a lot of variation in caffeine metabolism between individuals, though - I know I’m very sensitive to the effects of caffeine, and feel like a grandma with my 2pm cut-off, deeply envious of friends who can drink a coffee after dinner and fall asleep straight afterwards.

“caffeine increases your sleep latency (the time it takes to fall asleep), as well as decreasing the quality of your sleep”

Regular caffeine intake stimulates your body to increase the number of adenosine receptors in your brain, meaning you need to consume more and more caffeine to get the same effect. When you don’t get your regular fix, these adenosine receptors can cause blood vessels in the brain to dilate, causing a headache. Caffeine can block this dilation to relieve the headache, which is also why it’s found in many headache medications.

Studies about the effects of caffeine on long-term health have had mixed results, and are made more complicated by confounding factors. It’s likely that the negative health associations found in many early studies were actually down to the association between smoking and coffee drinking. More recent studies suggest that coffee and tea consumption could be linked to a lower risk of cardiovascular disease, type 2 diabetes and dementia. If nothing else, you could always make the argument that their cognitive benefits mean the Pret addiction is actually helping your degree…

Anyway, it was good enough for Isaac Newton, right?