Caffeine

Caffeine, also known as trimethylxanthine, coffeine, theine, mateine, guaranine, methyltheobromine and 1,3,7-trimethylxanthine, is a xanthine alkaloid found naturally in such foods as coffee beans, tea, kola nuts, Yerba mate, guarana berries, and (in small amounts) cacao beans. For the plant, caffeine acts as a natural pesticide since it paralyzes and kills some of the insects that attempt to feed on the plant.

Metabolism and toxicology

Caffeine is thought to act on the brain (and in fact, most cells of the body, since all cells have adenosine receptors) by blocking adenosine receptors (thereby blocking a pathway that leads to the breakdown of cyclic adenosine monophosphate, cAMP). 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.

Related Topics:
Brain - Adenosine - Cyclic adenosine monophosphate - Sleep - Hormone - Epinephrine - Blood pressure - Blood - Muscle - Skin - Organ - Glucose - Liver - Amphetamines - Neurotransmitter - Dopamine

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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.

Related Topics:
CNS - Stimulant - Alcohol

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In the liver, the first metabolic products of caffeine are three dimethylxanthines: theophylline (4%), theobromine (12%) and paraxanthine (84%). Theophylline relaxes smooth muscles of the bronchii and has been used as a treatment of asthma. Theobromine, the principal alkaloid in cocoa (chocolate) can increase blood vessel dilation and urine volume. Paraxanthine increases lipolysis, leading to elevated glycerol and free fatty acid in the blood plasma.

Related Topics:
Liver - Metabolic - Dimethylxanthines - Theophylline - Theobromine - Smooth muscle - Bronchii - Asthma - Cocoa - Chocolate - Blood vessel - Urine - Lipolysis - Glycerol - Fatty acid - Blood plasma

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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. Any accumulated sleep debt will be fully felt on withdrawal as well.

Related Topics:
Adenosine - Sleep debt

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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 1,000 mg 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.

Related Topics:
Insomnia - Diuresis - Gastrointestinal - Thought - Speech - Cardiac arrhythmia - Tachycardia - Psychomotor agitation - Panic disorder - Generalized anxiety disorder

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The minimum lethal dose ever reported was 3,200 mg, 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 an 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 10 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 children 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 hours 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.

Related Topics:
LD - Half life - Metabolize

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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).

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Intravenous caffeine (in the form of caffeine benzoate 500 mg over 1 hour) is occasionally used medically to treat post-lumbar puncture ("spinal tap") headachehttp://www.emedicine.com/neuro/topic557.htm.

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Although caffeine solutions are often used as a chemical standard for bitterness, caffeine is added to some soft drinks such as colas, Irn-Bru and Mountain Dew ostensibly for its taste.

Related Topics:
Bitterness - Soft drink - Cola - Irn-Bru - Mountain Dew

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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. Caffeine does more damage to spiders than drugs such as LSD, marijuana, benzedrine and chloral hydrate. {{fn|(1)}}

Related Topics:
Theobromine - Theophylline - Spider - LSD - Marijuana - Benzedrine - Chloral hydrate

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