How does caffeine keep us awake?




Over 100,000 metric tons of caffeine are consumed around the world every year. That’s equivalent to the weight of 14 Eiffel Towers! Caffeine helps us feel alert, focused, and energetic, even if we haven’t had enough sleep — but it can also raise our blood pressure and make us feel anxious. So how does it keep us awake? Hanan Qasim shares the science behind the world’s most widely used drug.







Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is the world's most widely consumed psychoactive drug. Unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world. 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 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). It is found in the seeds, nuts, or leaves of a number of plants native to South America and East Asia and helps to protect them against predator insects and to prevent germination of nearby seeds. The most well known source of caffeine is the coffee bean, a misnomer for the seed of Coffea plants. Beverages containing caffeine are ingested to relieve or prevent drowsiness and to improve performance. To make these drinks, caffeine is extracted by steeping the plant product in water, a process called infusion. Caffeine-containing drinks, such as coffee, tea, and cola, are very popular; as of 2014, 85% of American adults consumed some form of caffeine daily, consuming 164mg on average.




Caffeine can have both positive and negative health effects. It can treat and prevent the premature infant breathing disorders bronchopulmonary dysplasia of prematurity and apnea of prematurityCaffeine citrate is on the WHO Model List of Essential Medicines. It may confer a modest protective effect against some diseases, including Parkinson's disease. Some people experience insomnia or sleep disruption if they consume caffeine, especially during the evening hours, but others show little disturbance. Evidence of a risk during pregnancy is equivocal; some authorities recommend that pregnant women limit consumption to the equivalent of two cups of coffee per day or less. Caffeine can produce a mild form of drug dependence – associated with withdrawal symptoms such as sleepiness, headache, and irritability – when an individual stops using caffeine after repeated daily intake. Tolerance to the autonomic effects of increased blood pressure and heart rate, and increased urine output, develops with chronic use (i.e., these symptoms become less pronounced or do not occur following consistent use).

Caffeine is classified by the US Food and Drug Administration as "generally recognized as safe" (GRAS). Toxic doses, over 10 grams per day for an adult, are much higher than typical doses of under 500 milligrams per day. A cup of coffee contains 80–175 mg of caffeine, depending on what "bean" (seed) is used and how it is prepared (e.g. drippercolation, or espresso). Thus it requires roughly 50–100 ordinary cups of coffee to reach a lethal dose. However pure powdered caffeine, which is available as a dietary supplement, can be lethal in tablespoon-sized amounts.




Side effects

Physical

Caffeine can increase blood pressure and cause vasoconstriction. Long-term consumption at sufficiently high doses has been associated with chronic arterial stiffness. Coffee and caffeine can affect gastrointestinal motility and gastric acid secretion. Caffeine in low doses may cause weak bronchodilation for up to four hours in asthmatics. Caffeine increases basal metabolic rate in adults. In postmenopausal women, high caffeine consumption can accelerate bone loss.

Doses of caffeine equivalent to the amount normally found in standard servings of tea, coffee and carbonated soft drinks appear to have no diuretic action. However, acute ingestion of caffeine in large doses (at least 250–300 mg, equivalent to the amount found in 2–3 cups of coffee or 5–8 cups of tea) results in a short-term stimulation of urine output in individuals who have been deprived of caffeine for a period of days or weeks. This increase is due to both a diuresis (increase in water excretion) and a natriuresis (increase in saline excretion); it is mediated via proximal tubular adenosine receptor blockade. The acute increase in urinary output may increase the risk of dehydration. However, chronic users of caffeine develop a tolerance to this effect, and experience no increase in urinary output. 




Psychological


Minor undesired symptoms from caffeine ingestion not sufficiently severe to warrant a psychiatric diagnosis are common and include mild anxiety, jitteriness, insomnia, increased sleep latency, and reduced coordination. Caffeine can have negative effects on anxiety disorders. According to a 2011 literature review, caffeine use is positively associated with anxiety and panic disorders. At high doses, typically greater than 300 mg, caffeine can both cause and worsen anxiety. For some people, discontinuing caffeine use can significantly reduce anxiety.

In moderate doses, caffeine may reduce symptoms of depression and lower suicide risk.
Some textbooks state that caffeine is a mild euphoriant, others state that it is not a euphoriant, and one states that it is and is not a euphoriant.

Thanks to Wikipedia: Caffeine

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