How Does Caffeine Affect Brain Physiology?

Caffeine gives you that immediate boost to take on the day. But that added zip comes with complex, yet temporary, changes to your brain, the vital control system of your entire body. Your brain includes three main sections that break down into a multitude of structures, including the right and left hemispheres, the lobes within these hemispheres and the deep structures within each lobe. Caffeine can speed up how these complex systems work together to increase your energy for exercise or provoke clarity of thought, but it can also cause you to feel lethargic and irritable if you overdo it.

About Caffeine

Caffeine is one of the most widely used legal psychoactive stimulants in the United States, and it is found in more than 60 types of plants, notes the FDA. You likely consume it from synthetic sources added to foods, beverages and even medicine. When you consume any form of caffeine, it changes how the chemicals in your brain communicate to the rest of your body, and this is called a physiological effect. After you drink a few cups of coffee or eat a cocoa-rich chocolate bar, the caffeine is absorbed by your stomach and small intestine. Your liver metabolizes the molecules in caffeine, and it breaks down into the metabolites paraxanthine, theobromine and theophylline. These metabolites spark the chemical changes in your brain and stimulate your nervous system. Not everyone responds to caffeine the same, and it probably won't hurt you. But most people should limit their caffeine to 300 mg per day, notes MayoClinic.com. That's about the equivalent of a couple cups of coffee, or several cups of tea or sodas.

Blocks Adenosine

Adenosine, a naturally occurring chemical in your body, restricts the release of brain chemicals like dopamine so you can fall asleep and are not overstimulated with adrenaline from stress or anxiety. According to the 2002 study in the "American Journal of Physiology," caffeine's stimulating effect blocks adenosine. This result has the benefit of preventing fatigue so you are alert in the daytime after caffeine consumption, but also has a downside because caffeine can prevent you from sleeping restfully at night. Caffeine's effect on adenosine further alters the way it is released in your brain, because it normally increases when you are awake and wanes during sleep. This physiological change can ultimately affect other chemical systems that use adenosine, such as your blood vessels and muscles.

Alters Mood

You may notice a boost in your mood after your morning coffee, but when you use caffeine in larger doses it can induce acute anxiety and irritability. According to "Pharmacological Reviews," caffeine may have this mood-altering effect because it affects GABA receptors indirectly. Gamma-aminobutyric acid, or GABA, is a chemical receptor in your brain that binds with other neurotransmitters linked to your emotions and thoughts. Caffeine blocking your adenosine receptors causes another domino effect of preventing GABA from signaling your brain to have a steady emotion, resulting in mood fluctuations. As caffeine makes its rounds in your brain, it further stifles your pituitary gland from secreting hormones that regulate your energy level and motivation. Although you get that immediate burst of energy, your body grows weary over time without more caffeine, or your body is unable to keep up with the changes of excessive caffeine all at once.

Additional Physiological Changes

As a stimulant that affects your brain chemistry, caffeine also increases your blood pressure temporarily and causes rapid heartbeat. These are generally minor affects if you do not consume large quantities of caffeine. However, consult your physician regarding safe use of caffeine to prevent serious complications related to your cardiovascular health. You can become dependent upon or addicted to caffeine because it acts as a drug in your body, but this is preventable with moderation. As with any addictive substance, caffeine addiction can lead to tolerance, which means you eventually use more to achieve the same stimulating effects. Taking in 500 mg or more of caffeine a day is not safe, and can cause digestive upset, panic, heart palpitations and tremors.