Caffeine: The Good, the Bad, and the Ugly
Caffeine is consumed in mass quantities throughout the world. It is prized in many cultures for its ability to increase energy levels in the body and to enhance concentration. However, caffeine also has a down side; it can be addictive, cause withdrawal headaches, induce irregular heartbeat, and make sleeping problematic.
Probably the most common sources of caffeine are coffee, tea, and carbonated drinks. Caffeine is also found in chocolate, some nuts, and sometimes medicines. It is a white, crystalline substance, chemically known as trimethylxanthine (C8H10N4O2).
Although people have long known that coffee and tea have an energizing effect (perhaps as long ago as 3000 B.C. in China), they were not aware of caffeine specifically. In 1820 a brilliant German analytical chemist, Friedrich Runge, was asked by his friend, the poet Goethe, to look into coffee and see what it was about it that kept him from being able to sleep at night. Runge found a fine crystalline substance and called it caffeine. It was not until the late 1800s that the actual chemical structure of caffeine was determined by Herrman Fischer (work which helped to bring him the Nobel Prize in 1902).
The highest consumption of caffeine occurs in northern countries with temperate climates such as Sweden, England, the United States and Canada. The annual intake varies but on average the amount is greater than 200 milligrams per day.1 Caffeine absorption into the body from the intestinal tract is highly efficient and has been estimated as high as 99% (within 45 minutes of ingestion).
Caffeine in the Body
Caffeine can pass through all permeable membranes in the body partly because it is hydro-phobic. It hits peak concentration in the bloodstream between 15 minutes and two hours after it is consumed. Since it gets past barriers in the brain it can have a direct effect on the nervous system. It does this by taking the place of adenosine in adenosine receptors. In the brain adenosine is used as an inhibitor. When a person is awake the amount of ADP slowly increases, making a person more tired. In sleep the adenosine decreases, eventually allowing a person to awaken. Caffeine interferes with this process.2 These adenosine inhibitors also help prevent tremors, so the interference of caffeine could also induce or exacerbate tremors.3 (Adenosine is prominent in the ATP-ADP cycle.)
Caffeine has a half life in the body of about 4 and a half hours, which means it eventually runs out of the system, but it does take quite a while for this to happen. The half life is much quicker in smokers and slower in women taking contraceptives. People with liver disease will likely have even more trouble processing the caffeine.
The liver metabolizes the caffeine, changing it into three different substances:
- Paraxanthine (84%) - increases fatty acids and glycerol in blood plasma.
- Theobromine (12%) - increases urine volume and dilates blood vessels.
- Theophylline (4%) - is used to treat asthma because it soothes smooth muscles in the bronchi.
These substances are then in turn metabolized and excreted with urine.
Uses and Benefits of Caffeine
At one time it was thought that caffeine could be effective in diet pills. However, this proved not to be the case and the U.S. government ordered that it no longer be used. It is still often used in combination with aspirin to deal with headaches.4
Caffeine has been shown to be beneficial for many specific and general applications. It has been used in the treatment of ADHD and to relieve headaches after epidural anesthesia. Moderate coffee and tea consumption has been shown to reduce the likelihood of type 2 diabetes. Caffeine may delay the onset of Parkinson's disease and help prevent dizziness in older people. It may also help alleviate breathing problems in infants and mitigate the effects of asthma.5
Because pure caffeine is the byproduct of the process of making decaf coffee and tea, there is generally a lot of inexpensive caffeine available. Caffeine is one of the most studied substances consumed by humans. Even so, all of its effects and uses have not been completely explored. New studies come out constantly and will continue to expand our knowledge of caffeine.
Nutrition and the Food Pyramid
- Biology Online
- Science News
- Nature Medicine: Adenosine is crucial for deep brain stimulation–mediated attenuation of tremor
- WebMD: Uses of Caffeine