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There are several known mechanisms of action to explain the effects of caffeine.
The most prominent is that it reversibly blocks the action of adenosine on its receptor and consequently prevents the onset of drowsiness induced by adenosine.
Caffeine-containing drinks, such as coffee, tea, and cola, are very popular; in 2005, 90% of North American adults consumed caffeine daily.
Caffeine can have both positive and negative health effects.
It is the world's most widely consumed psychoactive drug.
Caffeine citrate is on the WHO Model List of Essential Medicines. One meta-analysis concluded that cardiovascular disease such as coronary artery disease and stroke is less likely with 3–5 cups of non-decaffeinated coffee per day but more likely with over 5 cups per day.It is found in the seeds, nuts, or leaves of a number of plants native to South America and East Asia and confers on them several survival and reproductive benefits.The most well known source of caffeine is the coffee bean, a misnomer for the seed of Coffea plants.Caffeine also stimulates certain portions of the autonomic nervous system.
Caffeine is a bitter, white crystalline purine, a methylxanthine alkaloid, and is chemically related to the adenine and guanine bases of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).Some people experience insomnia or sleep disruption if they consume caffeine, especially during the evening hours, but others show little disturbance.