Caffeine is America's most popular drug -- more than half of Americans over age 18 report drinking coffee daily, according to Harvard School of Public Health. Caffeine is naturally calorie-free and provides an energy boost because of its stimulant effect on brain physiology. Its effect on the brain can be advantageous under some circumstances, but it can also cause some side effects.
Caffeine: Adenosine's Fraternal Twin
Caffeine has the ability to affect the brain because it has a chemical structure similar to adenosine, a natural brain chemical. Normally, the body produces adenosine to help you unwind -- the adenosine binds to cells in your brain and you start to feel drowsy. Because caffeine has a similar molecular structure, it can bind to the same brain cells and prevents adenosine from doing its job, blocking the brain's natural "drowsy" signals. As a result, you feel more alert for a few hours after consuming caffeine, until adenosine starts working again.
Effect on Brain Function
Without fatigue-inducing signals from adenosine, the brain becomes more active. Consuming caffeine helps your brain temporarily work more efficiently, which improves cognitive function. One study, published in the June 2014 issue of the "Journal of Nutrition," found that people who consume caffeine do better on tests for memory, cognition and attention than those who don't. Caffeine's effect on the brain also helps you during workouts by increasing the amount of dopamine in your brain. This helps improve endurance during exercise, according to a study published in "Pharmacology, Biochemistry and Behavior" in July 2014.
While there are times when you need a brain boost, caffeine's stimulant effects are not always welcome. If you have caffeine late in the day, it can interfere with your brain's natural sleep signals and disrupt your sleeping cycle. Caffeine's stimulant effects on your brain also have other effects, including anxiety or a rapid heart rate. If you already have an underlying issue that affects your mental or cardiovascular health, check with your doctor before consuming caffeine.
Safe Caffeine Consumption
Most people can safely consume between 200 and 300 milligrams of caffeine per day, notes the University of Maryland Medical Center. That's about the equivalent of 3 cups of coffee. However, people who have chronic headaches, or who have panic attacks or anxiety disorders should avoid caffeine, because it can make them worse. Caffeine has no taste, so you can easily switch from caffeine-containing foods, like coffee and tea, to decaf versions without any difference in flavor.