Caffeine - Physical Effects Of Caffeine

Caffeine is classified as a stimulant because it increases the activity of the cardiovascular system, digestive system, and sympathetic nervous system (that which generally mobilizes the body for greater activity), and produces a sense of alertness in the brain. It also has a mild diuretic effect, eliminating water from the body by increasing urination. In moderate amounts, it can increase the ability to work longer and concentrate better. Too much caffeine, however, can produce nervousness, anxiety, irritability, and sleeplessness.

Because it gives athletes quicker reaction and longer endurance times, caffeine is a drug for which Olympic competitors are tested. If more than a small to moderate amount of caffeine (the amount in a few cups of coffee) is found in the blood, an athlete can be disqualified from the Olympic Games and other international competitions.

Many caffeine-producing plants also contain related stimulants known as methylxanthines, two of which are theophylline and theobromine. Theophylline is used in prescription drugs to treat chronic lung diseases such as asthma and emphysema. Theobromine is a weaker stimulant than caffeine, but it is more abundant in cocoa beans than is caffeine. Part of the stimulating effect of chocolate and cocoa is probably due to theobromine.

The fact that caffeine increases alertness has led to the myth that a strong cup of coffee will help to sober up someone who is drunk, but caffeine does not counteract the effects of alcohol.

How Caffeine Is Metabolized

In its pure state, caffeine is a bitter white powder that looks something like cornstarch. It is a member of the purine family of compounds. When purines are broken down in the body, they form a chemical called xanthine. The liver converts xanthine to uric acid, a metabolic waste product.

Caffeine dissolves in water, and it is rapidly and completely absorbed into the blood after ingestion. It takes from four to twelve hours to be eliminated completely from the body. Therefore, drinking coffee, tea, or caffeine-containing soft drinks several times a day can result in a large amount of caffeine in the body.

Two other purines, adenine and guanine, play a major role in human genetics and cell function. One of their by-products, adenosine, participates in the supply of energy to cells and helps regulate body processes such as the transmission of signals by nerves. In addition, adenosine can

• Promote sleepiness.
• Dilate blood vessels.
• Reduce the contractions of the stomach and intestines.
• Prevent seizures.
• Slow the reaction to stress.
• Lower the heart rate, blood pressure, and body temperature.

To perform these functions, adenosine inhibits the release of neurotransmitters (chemicals that carry messages from one nerve cell to another) by binding to specific receptors on a cell's surface. The structure of caffeine and its by-products is chemically similar to that of adenosine, which allows caffeine to bind to the same receptor sites, blocking adenosine and preventing it from taking effect. The effects of caffeine are the result of this blocking of the "slowing" effects of adenosine and explain why ingesting large amounts of caffeine may result in the "caffeine jitters."