Millions of people wake up every morning and get their daily kick-start through a cup of coffee. What is in this miracle drink that has it termed "America's most popular stimulant"? The answer is caffeine - which, though widely acknowledged as a quick pick-me-up, has many adverse long term effects on the body. Physical addiction is one of these, along with the increased tolerance that results from frequent usage. Caffeine manifests itself in a variety of ways when ingested, and these can best be understood by first explaining how caffeine works on a molecular level.

Caffeine begins with a basic molecule called xanthine. This molecule is normally found in plants, because caffeine-producing plants lack the enzymes that are present in animals which convert excess xanthine into other substances (urine in humans). These plants have an enzymatic assembly line where methyl groups are attatched to the xanthine. Depending on whether one, two or three methyl groups are attatched, the resulting molecule is either a methylxanthine, dimethylxanthine or trimethylxanthine. Caffeine is a specific type of trimethylxanthine. Two other types of dimethylxanthines are theophylline and theobromine, which differ only in the placement of the methyl groups. These are important because of the way that the liver disposes of caffeine, which it considers a poison, - it undoes the steps the molecules underwent while forming in the plant. The caffeine molecule becomes either theophylline, theobromine or paraxanthine, depending on which of the methyl groups is removed. Thus, even after the first step of metabolization, the molecule continues to act on the body. In the following steps, methyl groups continue to be removed until the basic xanthine is left, which is then excreted in urine. This is one reason it takes so long for caffeine to wear off - the body has to get rid of each component instead of the entire caffeine molecule. The breaking down of the molecules is also what allows them to be excreted through urine - without this process, caffeine's ready ability to pass through membranes would prevent its elimination by the kidneys, and caffeine would stay in the body for days.

When caffeine is ingested, it travels down the gastrointestinal tract to the stomach, where it is absorbed through the blood vessels embedded in the stomach wall. It then passes through the bloodstream to the liver, where it goes to the heart and is distributed throughout the entire body. Most importantly, it travels to the brain and muscles where it inhibits the function of a chemical called adenosine. Produced in the brain continuously during the day, adenosine binds to adenosine receptors on the surfaces of cells. The activity inside the cell slows and the movement of neurotransmitters in the brain is delayed, resulting in drowsiness. Adenosine receptors have a very specific shape, which caffeine mirrors. Caffeine does not join perfectly with the adenosine receptors - if it did, then it would be an identical depressant. Since caffeine differs slightly in shape from adenosine, it is instead a powerful stimulant. Caffeine binds itself to the adenosine receptors and occupies those spaces. Without the adenosine attatched to the receptor, the cell activity doesn't decrease. In the brain, neurotransmitters are fired at increased speeds, and nerve cell activity is heightened - this causes the mind and body to be alert and invigorated.

Caffeine causes escalated brain activity which triggers a chain reaction. The body thinks that there is an emergency and produces adrenalin, which manifests itself with dialated pupils, easier breathing, faster heartbeat, tensed muscles and excitement (which is a result of sugar being released into the bloodstream by the liver). Other physical effects include muscles twitching, such as compulsive hand tremors, headaches and the need to urinate, which is explained by the way in which caffeine is broken down.

In addition to physical influences, caffeine affects the brain. Dopamine, the "pleasure" neurotransmitter, is produced at an increased rate when caffeine is present, thus making the consumer feel good. In relation to intellectual tasks, caffeine increases the speed at which simple tasks are performed, yet anything involving short term memory and personality-based tasks become more difficult. Sleep is another brain function that is affected - while sleep is possible, REM sleep does not last as long when caffeine is present. This lack of deep sleep builds up, and with each successive day it is necessary to consume more caffeine in order to function normally.

Dependency occurs in many people who habitually ingest caffeine. When an "addict" tries to stop consuming caffeine they are assaulted with severe headaches as the blood vessels in the brain dialate. Other withdrawal symptoms are depression, an erratic heartbeat and exhaustion, which sets in as the adrenalin is reabsorbed. Being "on alert" for extended periods of time is very unhealthy - the human "fight or flight" survival mechanism was designed to be a temporary condition. In addition to acute dependency, caffeine consumers have to deal with increased tolerance. Specifically, when the body realizes that it's adenosine receptors are blocked, it creates more - thus, more caffeine needs to be consumed to take care of the extra receptors. Tolerance in humans, to a specific amount of caffeine, can develop anywhere from 7-12 days. Once accustomed to taking in that specific amount, any person who suddenly stops consuming caffeine will begin to show signs of withdrawal.

The general feelings of heightened awareness and pleasure that are results of habitual caffeine consumption are what hook the multitudes. Many don't think of the repercussions of their actions - as their tolerance increases, so does their intake. They do not realize that caffeine is addictive, and that once they stop getting their "fixes" they will experience severe withdrawal symptoms. No one had ever died of an overdose, but nonetheless, people should be made aware that caffeine is an addictive drug that has many negative long term effects on the human mind and body.

Bibliography

Braun, Stephan, Buzz, the Science and Lore of Alcohol and Caffeine, Oxford University Press, 1996

Snyder, Solomon H., The Encyclopedia of Psychoactive Drugs – Caffeine, Chealsea House Publishers, 1986

http://www.howstuffworks.com/caffeine.htm