How Caffeine Works

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Issue 17, Volume 110

By Angel Liu 

Coffee, energy drinks, and certain types of tea are a few of life’s natural energy potions. They’ve proven themselves to be loyal companions through late-night homework sprees, witching hour test crammings, and early morning classes, giving a burst of wakefulness when your eyes feel bleary and your head like lead. But through what mechanisms do their powers manifest? A shared ingredient amongst them all, caffeine, holds the answer.

In order to discover how lethargy is fought off, we must first understand how and why we get tired in the first place. The brain uses energy to sustain its functions and the base unit of energy in your body is adenosine triphosphate (ATP). ATP releases energy when it is broken down, leaving behind molecules of adenosine. The longer one is conscious, the higher their adenosine levels will be. Adenosine is able to bind with adenosine receptors in the brain, of which there are two major types: A1 and A2A. A1 receptors are found on neurons that compel the brain to stay awake, which adenosine slows down, and A2A receptors are found on neurons that compel the brain to rest, which adenosine speeds up. The combined force of the two types of receptors causes sleepiness.

Caffeine (C8H10N4O2) is a drug of the methylxanthine family that stimulates the central nervous system. Due to its similar chemical structure to adenosine (C10H13N5O4), caffeine is able to bind with adenosine receptors, effectively stealing adenosine’s spot. Unlike adenosine, however, caffeine does not chemically react with adenosine receptors, resulting in increased neural activity. This causes the pituitary glands to secrete hormones that activate the adrenal glands, which produce adrenaline, a hormone that causes the “fight or flight” response. Adrenaline causes elevated heart rates, blood pressure, blood flow to muscles, and sugar production rates in the liver and expands airways. Moreover, caffeine increases dopamine levels by slowing down dopamine reabsorption.

With great power comes great responsibility; thus, there are several drawbacks to consuming caffeine. When the body registers that caffeine is blocking its usual adenosine receptors and that it’s not feeling sleepy when it’s supposed to, it increases its number of adenosine receptors. One would need to consume even more caffeine to maintain the same level of alertness. This is called tolerance and as usage continues, it turns into dependence.

If you decided to stop consuming caffeine at some point, all of the artificially high numbers of adenosine receptors would bind with working adenosine, causing withdrawal symptoms such as headaches, fatigue, anxiety, irritability, a depressed mood, and an inability to concentrate. Thankfully, this is not a serious problem, as the number of adenosine receptors would return to normal as you continue to abstain from caffeine. It would be incorrect to say that caffeine could cause an addiction, as the dopamine surge it produces is not high enough to lead to the self-destructive drug chasing that characterizes addiction.

The effect of caffeine is not limited to the brain. Other organs, such as the heart and kidneys, also have A1 and A2A adenosine receptors. In these organs, adenosine continues to perform its job of slowing down activity, telling the heart to beat slower and the kidneys to produce less urine. This is why caffeine consumption causes increased heart rate and urine production. Other side effects include heartburn, upset stomachs, osteoporosis, and increased risk for miscarriage.

Caffeine is an integral part of many societies—from the tea houses of ancient China to the coffee stores that litter the streets of New York City. As students go to school and businesspeople to their offices, many of them hold a trusty cup of coffee in their hands. Look around a Stuyvesant classroom, and you’ll see the telltale signs of a plastic cup or paper bag, brown like the liquid they contain. There are entire plantations in the poorer parts of the world dedicated to farming tea or coffee. Caffeine is not just a trend—or even a phenomenon. It’s a culture.