Caffeine may lessen the severity of acute mountain sickness if taken a few hours prior to attaining a high altitude. One study found that decaffeinated coffee contained 10 mg of caffeine per cup, compared to approximately 85 mg of caffeine per cup for regular coffee. , Caffeine can delay or prevent sleep and improves task performance during sleep deprivation. Secondly, around the vascular bundles, where it probably inhibits pathogenic fungi from entering and colonizing the vascular bundles. , The metabolism of caffeine is reduced in pregnancy, especially in the third trimester, and the half life of caffeine during pregnancy can be increased up to 15 hours (as compared to 2.5 to 4.5 hours in non-pregnant adults). , Some analog substances have been created which mimic caffeine's properties with either function or structure or both. Thus, teas contain varying amounts of caffeine.  Peak blood concentration is reached within 1–2 hours. , Caffeine, as do other alkaloids such as cinchonine, quinine or strychnine, precipitates polyphenols and tannins. Renal Physiol.  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).. . In general, one serving of coffee ranges from 80 to 100 milligrams, for a single shot (30 milliliters) of arabica-variety espresso, to approximately 100–125 milligrams for a cup (120 milliliters) of drip coffee. Other sources include the leaves of yaupon holly, South American holly yerba mate, and Amazonian holly guayusa; and seeds from Amazonian maple guarana berries. , Since there is no antidote nor reversal agent for caffeine intoxication, treatment of mild caffeine intoxication is directed toward symptom relief; severe intoxication may require peritoneal dialysis, hemodialysis, or hemofiltration.  Current evidence regarding the effects of caffeine on pregnancy and for breastfeeding are inconclusive. , Death from caffeine ingestion appears to be rare, and most commonly caused by an intentional overdose of medications. a "total synthesis"), and two years later, he also derived the structural formula of the compound. In general, dark-roast coffee has very slightly less caffeine than lighter roasts because the roasting process reduces caffeine content of the bean by a small amount. (NTP, 1992). Thus it requires roughly 50–100 ordinary cups of coffee to reach the toxic dose. , 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. [a] In 1821, caffeine was isolated both by the French chemist Pierre Jean Robiquet and by another pair of French chemists, Pierre-Joseph Pelletier and Joseph Bienaimé Caventou, according to Swedish chemist Jöns Jacob Berzelius in his yearly journal.  The amount of caffeine needed to produce these effects varies from person to person, depending on body size and degree of tolerance. The first two disorders are classified under “Anxiety Disorder” and “Sleep-Wake Disorder” because they share similar characteristics. Plant Polyphenols: Synthesis, Properties, Significance. Bitter taste. However, chronic users of caffeine develop a tolerance to this effect and experience no increase in urinary output. Continued excessive use may lead to digestive disturbances, constipation, palpitations, shortness of breath and depressed mental states.  Common sources are the "beans" (seeds) of the two cultivated coffee plants, Coffea arabica and Coffea canephora (the quantity varies, but 1.3% is a typical value); and of the cocoa plant, Theobroma cacao; the leaves of the tea plant; and kola nuts. , Antagonism of adenosine receptors by caffeine also stimulates the medullary vagal, vasomotor, and respiratory centers, which increases respiratory rate, reduces heart rate, and constricts blood vessels. Nachdem Goethe mir seine größte Zufriedenheit sowol über die Erzählung des durch scheinbaren schwarzen Staar Geretteten, wie auch über das andere ausgesprochen, übergab er mir noch eine Schachtel mit Kaffeebohnen, die ein Grieche ihm als etwas Vorzügliches gesandt. National Oceanic and Atmospheric Administration. Evidence of a risk during pregnancy is equivocal; some authorities recommend that pregnant women limit caffeine to the equivalent of two cups of coffee per day or less.