Caffeine is a bitter, white crystalline xanthine alkaloid and a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants.
It is most commonly consumed by humans in infusions extracted from the seed of the coffee plant and the leaves of the tea bush, as well as from various foods and drinks containing products derived from the kola nut. Other sources include yerba maté, guarana berries, guayusa, and the yaupon holly.In humans, caffeine acts as a central nervous system stimulant, temporarily warding off drowsiness and restoring alertness.
Caffeine is classified by the Food and Drug Administration as GRAS (generally recognized as safe). Ordinary consumption can have low health risks, even when carried on for years – there may be a modest protective effect against some diseases, including Parkinson's disease, and certain types of cancer.
Some people experience sleep disruption if they consume caffeine, especially during the evening hours, but others show little disturbance and the effect of caffeine on sleep is highly variable.
Evidence of a risk to pregnancy is equivocal, but some authorities have concluded that prudent advice is for pregnant women to limit consumption to the equivalent of two cups of coffee per day or less. The American Congress of Obstetricians and Gynecologists (ACOG) concluded in 2010 that caffeine consumption is safe up to 200 mg per day in pregnant women.
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Common sources of caffeine are coffee, tea, soft drinks and energy drinks, caffeine supplements, and (to a lesser extent) chocolate derived from cocoa beans. Less commonly used sources of caffeine include the yerba maté, guarana and ilex guayusa plants, which are sometimes used in the preparation of teas and energy drinks. Two of caffeine's alternative names, mateine and guaranine, are derived from the names of these plants.
Tea contains more caffeine than coffee by dry weight. A typical serving, however, contains much less, since tea is normally brewed much weaker. Also contributing to caffeine content are growing conditions, processing techniques, and other variables. Thus, certain types of tea may contain somewhat more caffeine than other teas.
Caffeine is also a common ingredient of soft drinks, such as cola, originally prepared from kola nuts. Soft drinks typically contain about 10 to 50 milligrams of caffeine per serving. By contrast, energy drinks, such as Red Bull, can start at 80 milligrams of caffeine per serving. The caffeine in these drinks either originates from the ingredients used or is an additive derived from the product of decaffeination or from chemical synthesis. Guarana, a prime ingredient of energy drinks, contains large amounts of caffeine with small amounts of theobromine and theophylline in a naturally occurring slow-release excipient.
Chocolate derived from cocoa beans contains a small amount of caffeine. The weak stimulant effect of chocolate may be due to a combination of theobromine and theophylline, as well as caffeine. A typical 28-gram serving of a milk chocolate bar has about as much caffeine as a cup of decaffeinated coffee, although dark chocolate has about the same caffeine as coffee by weight. Some dark chocolate currently in production contains as much as 160 mg per 100 g – which is double the caffeine content of the highest caffeinated drip coffee by weight.
Various manufacturers market caffeine tablets, claiming that using caffeine of pharmaceutical quality improves mental alertness. These effects have been borne out by research that shows caffeine use (whether in tablet form or not) results in decreased fatigue and increased attentiveness.[13]These tablets are commonly used by students studying for their exams and by people who work or drive for long hours.
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