Caffeine

From Wikipedia, the free encyclopedia.

Caffeine is an alkaloid found naturally in such foods as coffee beans, tea, kola nuts, Yerba maté, guarana, and (in small amounts) cacao beans. It is added to some soft drinks such as colas, Irn-Bru and Mountain Dew.

Caffeine has a characteristic intensely bitter taste. Its main pharmacological properties are: a stimulant action on the central nervous system with psychotropic effects and stimulation of respiration, a stimulation of the heart rate, and a diuretic effect. Caffeine consumption leads to pharmacologic tolerance with defined withdrawal symptoms.

Sources

One common source of caffeine is the coffee plant, the beans from which are used to produce coffee.

One dose of caffeine is generally considered to be 100 mg. In theory, a single serving (5 fl oz / 150 ml) of drip coffee or one-half caffeine tablet would deliver this dose. In the real world, coffee varies considerably in caffeine content per serving, ranging from about 75 mg to 250 mg.

Tea is another common source of caffeine in many cultures. Black tea contains somewhat less caffeine per serving than coffee, (usually about half as much, depending on the strength of the brew), and green tea contains significantly less (usually about 10% as much, or 10mg / serving).

Soft Drinks such as Cola are also common. Such drinks typically contain about 25 mg to 50 mg of caffeine per serving. Some "Energy Drinks" such as Red Bull contain considerably more caffeine per serving, ranging from 100 to 400 mg.

Metabolism and toxicology

Caffeine is thought to act on the brain by blocking adenosine receptors. Adenosine, when bound to receptors of nerve cells, slows down nerve cell activity; this happens, among other times, during sleep. The caffeine molecule, being similar to adenosine, binds to the same receptors but doesn't cause the cells to slow down; instead, the caffeine blocks the receptors and thereby the adenosine action. The resulting increased nerve activity causes the release of the hormone epinephrine (adrenaline), which in turn leads to several effects such as higher heart rate, increased blood pressure, increased blood flow to muscles, decreased blood flow to the skin and inner organs, and release of glucose by the liver. In addition, caffeine, similar to amphetamines, increases the levels of the neurotransmitter dopamine in the brain.

Caffeine is quickly and completely removed from the brain and, unlike other CNS stimulants or alcohol, its effects are short lived. In many people, caffeine does not negatively affect concentration or higher mental functions, and hence caffeinated drinks are often consumed in the course of work.

Continued consumption of caffeine can lead to tolerance. Upon withdrawal, the body becomes oversensitive to adenosine, causing the blood pressure to drop dramatically, leading to headache and other symptoms. Recent studies suggest that caffeine intake (in coffee) may decrease the risk of developing Parkinson's disease, but additional study is needed.

Too much caffeine can lead to caffeine intoxication. The symptoms of this disorder are restlessness, nervousness, excitement, insomnia, flushed face, diuresis, gastrointestinal complaints, even hallucinations. They can occur in some people after as little as 250 mg per day. More than 1 g per day may result in muscle twitching, rambling flow of thought and speech, cardiac arrhythmia or tachycardia, and psychomotor agitation. Caffeine intoxication can lead to symptoms similar to panic disorder and generalized anxiety disorder.

The minimum lethal dose ever reported was 3.2 g, intravenously. The LD50 of caffeine (that is the lethal dosage reported to kill 50% of the population) is estimated between 13-19 grams for oral administration for a average adult. The LD50 of caffeine is dependent on weight and estimated to be about 150-200 mg per kg of body mass, roughly 140-180 cups of coffee for an average adult taken within a limited timeframe that is dependent on half life. The half-life or time it takes to metabolize 50% of the caffeine, ranges from 3.5 to 100 hours. In adults the half-life is generally around 5 hours. However contraceptive pills increase this to around 12 hours and for women over 3 months pregnant it varies from 10 to 18 hours. In infants and young child the half-life may be longer than adults. With common coffee and a very rare half-life of 100 hours it would require 3 cups of coffee every hour for 100 hour just to reach LD50. Though achieving lethal dose with coffee would be exceptionally difficult, there have been many reported deaths from intentional overdosing on caffeine pills.

While safe for humans, caffeine and its related compounds theobromine and theophylline are considerably more toxic to some other animals such as dogs, horses and parrots due to a much poorer ability to metabolize these compounds.

A fascinating recent finding is that intake of caffeine can up to halve a patient's risk of diabetes mellitus type 2. While this was originally noticed in patients who consumed high amounts (7 cups a day), the relationship has now been shown to be linear (Salazar-Martinez 2004).

Intravenous caffeine is often used medically to treat post-lumbar puncture ("spinal tap") headache.

Abuse and addiction

Caffeine, in its many forms, has been used for its stimulating effects. In modern times, though, the substance can be produced in much higher quantities, and has found its way into many products. Purer forms, such as those in caffeine pills, are available easily. These pills are sometimes used by college students and graveyard shift workers to last an entire night with no sleep.

Caffeine pills have been under media fire for recent and past deaths of students, usually take on the form of a caffeine overdose. One such example of this was the death of North Carolina student, Jason Allen. He swallowed most of a bottle of 90 such pills, which is the equivalent of 250 cups of coffee (or, alternatively, a gallon and a half (5 liters) of espresso, or 22 gallons (~150 liters) of Mountain Dew, which is not caffeinated in Canada for legal reasons). This was probably 18 grams of caffeine, since caffeine pills are restricted to 200 milligrams or less in the U.S., and most pep pill manufacturers make them in that size. A few other deaths by caffeine overdose have been known, almost always in the case of massive pill consumption on dares.

One dangerous form of caffeine use is to stay alert when one is under the influence of alcohol or in severe sleep debt. This tricks users into thinking they are more alert than they really are. Taking part in certain activities, such as driving, may be dangerous in such cases.