Did you know that caffeine is the most popular drug in the world? About 90% of North American adults consume caffeine daily, and the demand for coffee\u00a0just keeps growing!\u00a0Caffeine is found in over 60 kinds of plants. Tea and coffee are by far the most popular caffeinated beverages, but in Europe and the Americas, coffee reigns supreme.\u00a0 Coffee originates from the Kaffa region of Ethiopia. According to\u00a0legend, a goat shepherd named Kaldi first discovered the positive effects of coffee in the eighth century with the help of his flock. After eating the fruit and leaves of the coffea plant, the goats began to jump around like little kids hopped up on sugar. Kaldi tried one of the fruits for himself and felt energized. As the story goes, Kaldi kickstarted coffee consumption, and more and more people started eating the fruit for a buzz of energy.\u00a0 In the 1400s, coffee roasting techniques were developed, and coffee soared in popularity. Instead of eating the fruits of the coffea plant, we could roast the seeds and turn them into a delicious drink! The first recorded coffee house (Starbucks\u2019 ancient ancestor) opened its doors in Constantinople in 1554, and\u00a0in the early 17th century, coffee consumption spread to Europe.\u00a0 Now, people all over the world consume tea and coffee. But how does it give us energy? And what is all that caffeine doing to our bodies?\u00a0 How does caffeine make us alert? To understand how caffeine works, we first have to understand adenosine and its receptors. Adenosine is a purine nucleotide base\u2014you may be familiar with its role in ATP , the \u201cenergy molecule.\u201d\u00a0 The structure of adenosine. Image via\u00a0Wikipedia Commons.\u00a0 Located throughout the body, adenosine receptors affect the immune, nervous, circulatory, respiratory, and urinary systems. Adenosine contributes to\u00a0many functions, including the modulation of neurotransmitter release, vasoconstriction or vasodilation, and the regulation of T cell proliferation. Notably, adenosine causes sleep-inducing effects in the brain.\u00a0 When caffeine enters the body, it binds to the brain\u2019s adenosine receptors, blocking adenosine from binding to those same receptors. When adenosine is blocked, neurotransmitters like norepinephrine, dopamine, and gamma-aminobutyric acid are also affected. This is the main way caffeine alters our alertness and mood. The structure of caffeine. Image via\u00a0Wikipedia Commons.\u00a0 Have you ever experienced fatigue a couple hours after drinking caffeine? Caffeine crashes are caused when caffeine metabolizes away and all of the adenosine that\u2019s been building up\u00a0floods back into the receptors, triggering feelings of tiredness. Caffeine also affects the movement of calcium between cells. Neurotransmitters rely on the calcium that travels into nerve endings, and low concentrations of caffeine cause the endoplasmic reticulum to increase its uptake and release of calcium, though high levels of caffeine inhibits the endoplasmic reticulum\u2019s calcium uptake.\u00a0 Caffeine can also prevent cyclic adenosine monophosphate (cAMP) from being broken down, and buildup of cAMP causes the release of hormones like dopamine. However, the dose of caffeine required to do this would be toxic to humans.\u00a0 Caffeine\u2019s effects: The good, the bad, and the ugly\u00a0 Let\u2019s take a look at the effects of caffeine on the body, starting with its effects on the brain and ending with caffeine withdrawal symptoms.\u00a0 Caffeine and the brain\u00a0 Research indicates that about two cups of coffee can elevate your mood\u2026 but anyone with a \u201cDon\u2019t talk to me before I\u2019ve had my coffee\u201d mug could tell you that! The positive effects of caffeine on mood can last up to three hours. Heavy use of caffeine, however, can lead to tension, anxiety, and more intense physical symptoms.\u00a0 Because you feel less tired and bored, you\u2019re able to focus and perform better\u00a0after consuming caffeine. Some studies have indicated that caffeine decreases reaction times in auditory and visual choice tasks, while other cognitive skills like basic math seem to be unaffected.\u00a0 A study concluded that caffeine was connected to greater memory retention\u2014but not memory acquisition\u2014in rats, though\u00a0other studies\u00a0say that, broadly speaking, caffeine does not affect learning and memory tasks in humans. A lot of\u00a0research says that\u00a0caffeine improves physical reaction time and can improve coordination, speed, and agility. Caffeine leads to\u00a0an increase in adrenaline, the \u201cfight or flight\u201d hormone that prepares the body to act fast in the event of a threat. Caffeine and the heart Caffeine is a vasoconstrictor: it decreases the size of blood vessels. This triggers a temporary increase in blood pressure and heart rate. Blood pressure can stay elevated for up to three hours after consumption! Notably, these temporary effects are less likely to happen the more caffeine you drink habitually. The body can build up a tolerance to caffeine that can stave off its effects. If you have high blood pressure and you\u2019re concerned about caffeine, don\u2019t worry\u2014caffeine is\u00a0unlikely\u00a0to have long term, serious effects on your blood pressure. Caffeine increases heart rate and\u00a0can cause the ventricles to skip heartbeats, but\u00a0researchers are split\u00a0on whether or not caffeine leads to heart disease.\u00a0Some studies\u00a0indicate that caffeine consumption can decrease the risk of heart failure, while other scientists say that more research is necessary before we can come to any conclusions. Doctors emphasize that a moderate amount of caffeine (4-5 cups of coffee or tea a day) is likely safe.\u00a0 Sleep People love caffeine\u2019s effects on alertness and energy, but that energy boost\u00a0can come at a cost. People who habitually consume caffeine can suffer from altered circadian sleep schedules and overall sleep insufficiency.\u00a0 Researchers have pointed out\u00a0that in some cases, rather than increasing performance, caffeine might just restore performance lost by sleepiness. Why is sleep so important anyway? Poor sleep has been connected to\u00a0disorders like\u00a0depression, high blood pressure and heart disease, and diabetes. Sleep has been found to\u00a0play a role\u00a0in:\u00a0 Memory and learningImmune functionMetabolismMood Caffeine isn\u2019t a perfect solution for sleep deprivation.\u00a0A 2021 study\u00a0asked participants to complete a simple task and a more complicated task that required steps completed in a certain order. Sleep deprivation plus caffeine resulted in success with the easier task, but the caffeine could not help participants complete the more difficult task. The researcher emphasized that caffeine is not a replacement for sleep.\u00a0 Caffeine withdrawal\u00a0 Doctors have been writing about caffeine withdrawal for over two hundred years, but it wasn\u2019t listed in the\u00a0Diagnostic and Statistical Manual of Mental Disorders\u00a0(DSM)\u00a0until 2004. Symptoms of caffeine withdrawal include:\u00a0 HeadacheFatigueDepressed mood or irritability\u00a0Difficulty concentratingMuscle pain or stiffnessIrregular heartbeatIncreased respiratory rateDecreased or increased blood pressure Symptoms tend to start 12 to 24 hours after you stop drinking caffeine, and they can last up to nine days. Headaches occur in about half of caffeine withdrawal cases, and \u201cclinically significant distress or functional impairment\u201d occurs in about 13% of cases. You don\u2019t have to be a hardcore coffee drinker to get caffeine withdrawal: one study showed that withdrawal symptoms can occur after three days of caffeine consumption! Quitting cold turkey is sure to lead to headaches and grouchiness, but the good news is that caffeine withdrawal symptoms can be mitigated by gradually decreasing caffeine consumption.\u00a0 Conclusion Caffeine is popular worldwide for its effects on energy levels and alertness. In fact, this very blog post was written under the effects of a Dunkin\u2019 iced coffee! It binds to adenosine receptors, preventing adenosine from triggering sleepiness. Caffeine makes people more alert, more awake, and can improve reaction time. It can increase heart rate and blood pressure, but more importantly, it can interfere with sleep. Habitual caffeine consumers can experience withdrawal symptoms that make quitting caffeine difficult, but gradually decreasing consumption can be effective.\u00a0 Next time you have a cup of coffee or tea, eat a piece of chocolate, or drink a cola, think about how caffeine affects your body and your alertness!