TL;DR: Caffeine is a powerful, yet quite safe, stimulant drug that functions by blocking adenosine, an inhibitory neurotransmitter, leading to feelings of wakefulness and alertness.
Let us just start by saying that, we are not doctors. This article is not medical advice, nor should it be treated as such. This article is purely for educational purposes. Finally, we do not condone the use of any illegal substances nor the use of any prescription drug without a say-so from your physician.
Intro
There’s no better way to start your day than with a nice hot cup of coffee. One sip of that bitter, black liquid and it’s off to the races. From construction sites to poorly lit office buildings, caffeine is the 21st century workers drug of choice. But what is it about this strange little chemical, found in beans and leaves, that helps the world keep turning?
This article will provide an overview of caffeine, including what it is, how it works, its effects when consumed, as well as a few health concerns to be aware of. So pour yourself a big, steaming cup of coffee and join us as we delve into the stimulating world of caffeine.
What is Caffeine?
Caffeine is a popular stimulant drug (read more about drug classifications in our intro to drugs here) regularly consumed by many across the world. In fact, caffeine is the most widely used psychoactive drug in the world, with over 10 million tonnes of coffee beans being consumed globally in 2020 [1].
Caffeine is a naturally occurring substance that is found in the fruits, nuts and seeds of many equatorial plants. Caffeine is used by plants to both defend against herbivores eating them, as well as preventing the seeds of other plants from germinating, thus reducing competition.
The most common source of caffeine is from coffee, however it is also abundantly found in many other drinks such as tea, pop and energy drinks. Caffeine can also be found in higher doses in supplements, which usually come in pill or powder form.
Consuming caffeine leads to increased feelings of wakefulness, alertness and focus. As such, many people consume caffeine in the morning to shake off any sleepiness left over from the previous night and jump start their day. Some find it hard to even start their day before they’ve had their cup (or three) of coffee.
How Does Caffeine Work?
When you are awake, the firing of neurons in your brain produces a by-product known as adenosine. Adenosine is a useful chemical to have, as it helps to move energy throughout our cells by forming molecules like adenosine triphosphate (ATP) and adenosine diphosphate (ADP) [2]. Adenosine widens blood vessels and helps to regulate heart rhythm. It has also been found to be an effective natural painkiller.
Adenosine is classified as an inhibitory neurotransmitter. This means that when adenosine binds to adenosine receptors it depresses our central nervous system, slowing down many processes involved in wakefulness. As such, the higher levels of adenosine, the more tired you will feel.
The only way for our bodies to get rid of adenosine is to sleep. As our neurons fire throughout the day, more and more adenosine builds up, making us feel more and more tired. This build up, and subsequent need to clear it with sleep, has been proposed as one of the theories as to why we sleep. The chart below shows the amount of adenosine in various parts of a sleep deprived person’s brain. You can see the adenosine levels rising as the person becomes more and more sleep deprived, only being reduced when they are finally allowed to sleep (i.e. recover).
So, we’ve established that the amount of adenosine in someone’s body is correlated with feelings of tiredness. From this, it would stand to reason that reducing or preventing the production or uptake of adenosine would help to reduce feelings of tiredness. This is where caffeine comes in.
Caffeine and adenosine have very similar chemical structures. You can see a side by side comparison of each molecule below. Note how the components highlighted in green are almost identical.
This similarity allows caffeine to bind to the adenosine receptors in your brain. Now when adenosine is produced from brain activity, it has no receptors to bind to, as they are all clogged up with caffeine. This prevents your brain from “seeing” that there is adenosine present, so instead of slowing down, neural activity actually begins to speed up.
This increase in neural activity makes your brain think that something is up, and that there may be some sort of emergency going on, so it releases hormones that signal your adrenal glands to start producing adrenaline (epinephrine). This release of adrenaline makes you feel much more alert and energized, as well as having the following effects on the body [3].
- Your pupils dilate.
- The airway opens up (this is why people suffering from severe asthma attacks are sometimes injected with epinephrine).
- Your heart beats faster.
- Blood vessels on the surface constrict to slow blood flow from cuts and increase blood flow to muscles.
- Blood pressure rises.
- Blood flow to the stomach slows.
- The liver releases sugar into the bloodstream for extra energy.
- Muscles tighten up, ready for action.
In summary, caffeine functions by essentially tricking your body into thinking it is less tired than it is through the blocking of adenosine receptors. This in turn makes your body think there is some sort of emergency, prompting it to release adrenaline, making you feel alert and energized.
Effects of Caffeine
Along with reducing effects of fatigue and drowsiness, caffeine has been shown to increase both mental and physical performance. At normal doses it has been shown to improve reaction time, wakefulness, and motor coordination, while having inconsistent effects on learning and memory. It can delay or prevent sleep, and increases performance while sleep deprived. Tired workers have been found to make less mistakes while using caffeine. [1]
Caffeine also improves athletic performance, both in anaerobic and aerobic scenarios (read more on anaerobic vs aerobic systems here). Moderate doses can improve sprint times, cycling and running times and endurance. It also increases the basal metabolic rate in adults. Caffeine is helpful when lifting weights as well, improving muscular strength and power and reducing perceived exertion. While a reduction in perceived exertion does not directly increase the amount of weight lifted, it has been shown to greatly improve performance during resistance training, except for when exercising to exhaustion. [1]
These effects of caffeine are most prevalent 1 hour after consumption and generally taper off after around 3-4 hours. [1]
Health Concerns of Caffeine
In general, caffeine is considered quite a safe and harmless drug which is in part why it is so popular and widely used. However, at higher doses and with extended use some health complications do become prevalent. Some health concerns involved with caffeine are summarized below.
Negative Psychological Effects
Many users of caffeine experience mild, yet unpleasant symptoms from consuming caffeine, including mild anxiety, jitteriness, insomnia, increased sleep latency, and reduced coordination. People with pre-existing anxiety disorders are especially prone to experiencing anxiety while using caffeine. High caffeine doses over 300mg are positively correlated with inducing and worsening anxiety. [1]
Fortunately, as a tolerance to caffeine begins to form, most of these symptoms seem to disappear, so the negative psychological effects are really only a problem for irregular users. Interestingly, as tolerance increases, sensitization to some of the positive effects of caffeine, such as feelings of alertness and wellbeing, begins to occur. This means that the more someone uses caffeine, the more powerful these positive effects will become [1].
Addiction/Dependence
Essentially every modern business has at least one, the insufferable “Don’t talk to me until I’ve had my coffee” type (I’m looking at you, Barbara). While you may think they’re just being obnoxious, there is some real justification as to why they feel that way.
While the addiction mechanism of caffeine is disputed, as in some cases consuming high amounts of caffeine actually leads to aversion rather than addiction, there has been evidence for clear dependence and withdrawal mechanisms as a result of high caffeine consumption.
Symptoms of caffeine withdrawal begin to appear 24 hours after the reduction of regular caffeine usage. Withdrawal can appear in users who regularly consume at least 100mg of caffeine per day (about 1 – 1.5 cups of coffee), with users who consume more experiencing more intense withdrawal. Symptoms include difficulty concentrating, depressed mood/irritability, flu-like symptoms, headache, and fatigue [1]. For those trying to kick a caffeine habit, it may be worthwhile to slowly reduce your caffeine intake over time, rather than fully stopping all at once, cold-turkey.
Overdose
Overdosing on caffeine is quite difficult and uncommon, as the active dose is much lower than the lethal dose. Caffeine is considered lethal at doses higher than 10g per day, which is quite a lot considering your average cup of coffee has about 80-175mg of caffeine. This means that in order to poison yourself, you’d need to down about 50-100 cups of coffee to do so. However, it is worth noting that with dietary supplements of pure caffeine, a lethal dose can be contained in a tablespoon. [1]
Caffeine overdoses do happen from time to time, but in most cases it is from the intentional overconsumption of medication or supplements. This means that your average coffee/energy drink enjoyer really has not much to worry about, in regards to overdosing.
Children
While research is limited on the effects of caffeine on children, it is generally recommended that children consume little to no caffeine. While doses under 400mg are generally considered harmless for children, doses in excess can cause physiological, psychological and behavioral issues. [1]
A common urban myth is that caffeine stunts growth in children, however there is no scientific evidence to support this.
Children are generally already endless little balls of energy, so there really isn’t much reasoning to give them a drug that makes them even more energetic.
Conclusion
Caffeine is a safe, yet powerful drug. It blocks the receptors of adenosine, an inhibitory neurotransmitter, leading to increased feelings of energy and alertness. Using caffeine has been shown to increase both mental and physical performance. Although some mild negative symptoms may occur when using it, the chance of overdosing from regular usage of caffeine is slim to none, so if you need a little boost go ahead and pour yourself a nice cup of coffee. Just try to not go overboard as some mild, yet uncomfortable, withdrawal symptoms can begin to come through at higher doses.
References:
[1] https://en.wikipedia.org/wiki/Caffeine
[2] https://www.verywellhealth.com/adenosine-and-sleep-3015337
[3] https://science.howstuffworks.com/caffeine4.htm
