Coffee and tea. Those are beverages that many Americans (and people elsewhere in the world) seemingly cannot live without. On an average day, over half of all Americans will drink at least one cup of tea. The numbers are similar for daily coffee-drinkers and certainly there must be some people that drink both in one day (myself included).

While the act of drinking a warm beverage itself can be soothing, many coffee and tea drinkers are after something a little more direct: Caffeine.

What Caffeine Does

Caffeine might seem to be simply boosting your energy and waking you up in the morning, but it actually has a wide range of effects on the human body. When someone sleepy drinks caffeine, they get an increase in both their thinking ability and their memory. Their physical abilities are also improved. Stamina, endurance, and even sprint speed are mildly increased with caffeine use.

Caffeine comes with a variety of less useful side effects too. Even at moderate doses, caffeine can cause insomnia, anxiety, increased heart rate, and general feelings of jitteriness. Caffeine also causes more stomach acid to be produced, which can cause stomach upset in some people. Unsurprisingly, these side effects increase with higher doses.

How Caffeine Does It

The place where caffeine has most effect is the brain. The brain is full of various neurotransmitters, hormones, and signalers. Adenosine is one of these molecules floating about in your gray matter. Adenosine is created in the brain and there are specialized neuron receptors that match to it. When adenosine binds to these receptors it causes a feeling of drowsiness. The more adenosine that binds, the more sleepy a person will feel. Nerve cell activity slows and blood vessels in the brain dilate, letting oxygen flood the brain in preparation for sleep.

Due to the shape of its molecule, caffeine can also bind to adenosine receptors. When caffeine binds, the receptors don’t signal for sleep. It is similar enough to adenosine to take its place on receptors, but not similar enough to carry out the same function. With caffeine molecules taking up space on the receptors, adenosine is unable to bind. The brain becomes no longer able to signal for sleepiness once enough caffeine gets in its system.

Caffeine really stirs up the brain, making neurons more active. The pituitary gland misinterprets this activity as a sign of emergency and releases adrenaline into the bloodstream. Adrenaline is the “fight or flight” hormone, and it causes the heart to beat faster, pupils to dilate, airways to open, and liver to unlock extra sugar in case of sudden action.

Dopamine is another molecule that gets caught up in the caffeine cascade. Dopamine is associated with reward and is released when the body experiences something pleasurable, such as good food, sex, or favorite hobbies. Caffeine activates higher levels of dopamine production which results in a feeling of wellbeing after drinking a cup of a favorite caffeinated beverage. Of course, caffeine using dopamine to make us feel good is exactly why it can be a hard habit to kick.

If you have a hard time waking up in the morning without a cup of coffee, your body may have become reliant on caffeine and slowed production of its natural wakefulness hormones.

Caffeine Dependence

Caffeine addiction (pathological and compulsive use) has not been shown to occur in humans, but dependence has. People that consume at least 100 mg of caffeine per day (only one cup of coffee) are at risk of becoming dependent on caffeine. Those who are dependent on caffeine will experience some combination of lethargy, headaches, irritability, and nausea after 12-24 hours without it. This is called withdrawal, and some neurologists think it should be treated as a psychological disorder. Caffeine withdrawal can last for as many as nine days, making it a painful process to go through for those trying to cut back on a coffee habit.

Caffeine Health Benefits

When consumed over the course of years, caffeine can have significant health benefits. Drinking only two cups per day can improve long term memory. Three cups can reduce rates of liver cancer by 50%. If you drink four cups a day, your risk of developing mouth and throat cancer is halved! Additionally, Harvard researchers have found evidence that 2 – 4 cups of coffee per day can decrease suicide risk. A variety of other experiments have shown that regular caffeine consumption could also help prevent Parkinson’s disease, strokes, heart disease, and type 2 diabetes.

In the short term, caffeine can help lessen the blow of migraines and cluster headaches by tightening the blood vessels of the brain and reducing inflammation. Since caffeine opens up airways of the lungs, it also is a boon to asthmatics. Everybody responds a little differently to caffeine, so while one person may benefit from 2 cups of coffee a day, another might be driven to insomnia and anxiety. Still, caffeine can give a boost to daily functioning and lifetime health under the right conditions.

- Kate Dzikiewicz, Paul Griswold Howes Fellow