Assessments for the second year of my PhD are coming to a close and, although I don’t drink coffee, caffeine would be very much appreciated right now. As the most popular drink in the world, why not find out how it keeps us awake, and why it’s so addictive!
It is thought that ~400 billion cups of coffee are consumed around the world each year, with 450 million in the US every day! On average, each coffee drinker in the US is consuming 3 and a half cups a day. Scandinavia has the highest per-capita coffee consumption, with the average drinker consuming more than 4 cups a day. Coffee has been brewed since the 9th century, albeit in a much cruder manor then. Coffee beans are grown in over 50 countries across both South and Central America, Asia, Africa and the Caribbean, and more than 25 million farmers rely on coffee crops. Coffee is well known for containing caffeine, the most popular psychoactive drug in the world, found not only in coffee but also tea, energy drinks and much more.
Why does caffeine keep you awake? Caffeine changes our brain chemistry by blocking the natural production of a chemical which is associated with sleep: adenosine. Adenosine causes drowsiness as it slows nerve cell activity and makes blood vessels dilate, to allow more oxygen in whilst we sleep. Caffeine looks very similar to adenosine, and results in the inhibition (i.e. blocking) of nerve cell receptors. Adenosine would usually cause these cells to slow down but, when nerve cells are blocked, they speed up. This leads to increased neuron firing in the brain, causing the pituitary gland to think it is an emergency and, in-turn, produce hormones like adrenaline, giving you a “buzz”. A drug which increases neural activity is a stimulant. Examples of other stimulants include cocaine, nicotine, ecstasy and amphetamines. Caffeine also causes blood vessels to constrict, which is useful in some headache tablets (which sometimes contain caffeine) because constricting blood vessels can relieve the pain.
Caffeine is a drug, but why is it addictive? In 1994, it was established that caffeine is chemically addictive. Soon after you have ingested caffeine, it is absorbed through your small intestine and dissolved into your bloodstream, finally entering the brain. As already stated, this aids the stimulation of adrenaline, and the effects can last for 4-6 hours. People who regularly have caffeine will actually change their brain chemistry and some physical characteristics. Overtime, the brain will try to produce more adenosine receptors in an attempt to maintain equilibration to combat the caffeine. Therefore, coffee drinkers build up a tolerance and require more caffeine for the same buzz. If you quit a drug, be it cocaine, nicotine or caffeine, you will have withdrawal. First symptoms of caffeine withdrawal will include fatigue, both muscular and mentally, irritability and a lack of alertness. Over time, these effects can change to throbbing headaches, nausea and flu-like symptoms. These effects are relatively short-lived compared to other drug addictions, lasting only 7-12 days whilst the brain resets its number of adenosine receptors.
As caffeine is an addictive drug, what are safe consumption levels? Research has found that up to 400 mg a day (~4 cups of coffee or 10 coca colas) is safe for most healthy adults. Adolescents, children and pregnant/breastfeeding women should avoid caffeine and not mix it with alcohol. A few caffeine side-effects include a faster heartbeat, stomach upsets and tremors, and some people will be more sensitive to caffeine than others depending on weight, age, genetics, mental conditions etc. It is advised not to have caffeine late in the day as it can mask sleep deprivation, and interfere with your normal sleep cycle.
What about the perfect cup? How do barista’s make the same coffee beans you have at home, taste so much better? Science helps us to brew the best. Both chemistry and physics are involved. For those of you that like an espresso, the standard coffee constituents make up 8-10% of the drink which is perfectly executed by an espresso machine. There are very few technologies that can replicate this. However, those who prefer a weaker cup, are looking more at 1.2-1.5% coffee mass, easily reproduced by French or Turkish presses for example. How about taste? Temperature, grain size, water chemistry, brew time, and water-coffee ratio are all factors which contribute to taste. To find out more about coffee taste and perfect brewing, check out this article from Smithsonian: https://www.smithsonianmag.com/science-nature/science-behind-brewing-great-cup-coffee-180965049/
With so much coffee consumed daily, it is no wonder there are seemingly endless coffee shops and chains popping up everywhere. Consider your consumption of this drug: Just because it is legal does not mean it cannot be damaging if abused. Although, it would be good to know how to make those creamy coffees at home too.