Our Friend Caffeine


Welcome, new student, to Southampton.

Whilst at university you are sure to make many friends and acquaintances, some who will last  forever, others who you may only know briefly. But one friend that will see many of you through your whole time here: all the ups and downs, the highs and lows; is caffeine. This drug, unique in its ubiquitousness throughout culture, has been consumed by humans, it is estimated, for roughly 10,000 years, in one form or another. But is it really friend or foe?

In its pure form, 1,3,7-trimethylxanthine is a bitter white powder. Naturally, it is found in plants such as the cocoa, coffee, kola, guarana (you’ll often see this listed as an ingredient in energy drinks) and tea plants. You might wonder what use a plant might have for evolving an ability to make caffeine, a complex molecule which would require no insignificant amount of energy for the plant to produce. Until recently, this baffled scientists as well.

For one thing, methylxanthines are used as pesticides by humans and plants alike, to paralyze and kill off insects that would eat the leaves. However, some plants, including coffee and certain members of the citrus family, contain caffeine in their nectar as well as their leaves, and it turns out that bees, unlike other insects, are not so susceptible to this poison. In fact, the caffeine dose can actually increase the bee’s memory of a particular plant.

Caffeine in nectar can improve a bee’s memory of a flower

But now to address our own relationship with this drug, which is indeed a rather peculiar one. For instance, many of you will pay 2 to 3 times as much for 12oz of the stuff as you will for an entire litre of petrol or diesel, which does  seem ridiculous, but it isn’t without its uses. Increased alertness; task switching (also known as multi-tasking – your brain is not actually able to focus on two tasks at once, it just gets better or worse at switching quickly between them); and the ability to pay attention to meaningful sources while ignoring irrelevant ones (known as selective attention), are among brain processes shown to benefit from moderate doses of caffeine. Very useful to the student trying to cram revision for exams, then.

So how does it work? There is a chemical naturally in your brain called adenosine which bonds to certain receptors, calming nerve cells and inducing sleepiness. Caffeine, being structurally similar to adenosine, can bind to these receptors, blocking them off from adenosine, but does not induce the same sleep-ready state, and allows stimulants in your brain, such as dopamine and glutamate to excite neurons as they would naturally do. This is what creates the buzz you feel when you drink your double shot cappuccino or can of energy drink. The caffeine concentration in your blood peaks anywhere between 45 minutes and 2 hours after intake, with a half-life of around 5 hours, meaning that after 5 hours, the concentration is halved.

As well as this, the increased neuron firing induced by the effect of caffeine is picked up on by the pituitary gland, which releases hormones telling the adrenal gland to in turn release adrenaline – your body reacts as if in a fight or flight situation. The consequence of this is that your pupils dilate; the superficial blood vessels (the ones near to the surface) constrict to prevent bleeding excessively from wounds, and increase blood flow to muscles and vital organs; your heart rate and blood pressure rise; and the liver releases sugar into the bloodstream for extra energy.

The extra energy is beneficial in the short term, and caffeine has been shown to increase the effectiveness of aspirin in treating migraines, which could be to do with the blood vessels constricting. However, although these short term benefits exist, prolonging the body’s acute stress responses can lead to chronic stress, long term high blood pressure, and heart problems.

The drawbacks of caffeine consumption are more likely to occur in those with a twenty-cup-a-day habit, so to speak. Our bodies can become used to consuming caffeine, building up a tolerance, and requiring you to take in more caffeine in order to stimulate the brain and fight fatigue. Withdrawal symptoms include anything from a mild headache to migraines and tremors, but far from the severe withdrawal of other drugs, you’ll be fine in a day or two.

Jordan Stewart Science Enviroment 1
Too much caffeine can cause irratability, anxiety and insomnia. Image by Jordan Stewart.

Still, with the above health benefits and risks considered, doctors recommend no more than 300mg of caffeine consumption a day, because whilst between 200-300mg can elevate mood, more than 400-500mg can cause irritability, anxiety, insomnia, and more severe health risks. With 150mg in an average cup of coffee, and 80mg in a cup of tea, this means limiting yourself to 2-3 cups a day, which may come as a surprise to more than a few PhD students who have been wondering where they can get their caffeine intravenously.

So, though caffeine may seem to be our friend most of the time, we may want to limit the time and money we spend on it to keep ourselves fit for other social engagements.



Physics student and regular freelance science communicator, shooting for the stars. I'm your Science Editor and with the help of a team of talented writers, strive to bring you the most interesting and relevant science stories.

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