Book 1 Reading and Speaking (Л.Н. Шевырдяева - Naturally Speaking & Listening), страница 11

Higher doses induce jitteriness and anxiety. The fatal dose is about 10 grams.How does caffeine work? Caffeine blocks receptors for the neurotransmitter adenosine, which is generallyinhibitory and associated with the onset of sleep. Also raises dopamine levels, and stimulates the release of thefight-or-flight hormone adrenalin (From Newscientist.com).What is coffee? Raw coffee beans are the seeds of plants belonging to the Rubiaceae family, whichcomprises at least 66 species of the genus Coffea.

The two species that are commercially exploited are Coffeaarabica, which accounts for two thirds of world production, and C. canephora, often called robusta coffee, with onethird of global output. Robusta coffee plants and all wild coffee species have 22 chromosomes, whereas arabicahas 44.

Therefore, arabica and other coffee species cannot be crossed to produce a hybrid plant.Robusta is a high-yielding and disease-resistant tree standing up to 12 meters tall that grows best in warm,humid climates. It produces a cup featuring substantial body, a relatively harsh, earthy aroma, and an elevatedcaffeine content that ranges from 2.4 to 2.8 percent by weight. Although robusta is sold by many purveyors, it doesnot give rise to the highest-quality coffee.Arabica, which originated in the Ethiopian highlands, is a medium- to low-yielding, rather delicate tree fromfive to six meters tall that requires a temperate climate and considerable growing care.

Commercially grown coffeebushes are pruned to a height of 1.5 to 2.0 meters. Coffee made from Arabica beans has an intense, intricatearoma that can be reminiscent of flowers, fruit, honey, chocolate, caramel or toasted bread. Its caffeine contentnever exceeds 1.5 percent by weight. Because of its superior quality and taste, arabica sells for a higher price thanits hardy, rougher cousin.A good rainfall induces coffee plants to blossom, and some 210 days afterward red or yellow fruit calledcherries appear.

Each cherry contains two oblong seeds—the coffee beans. The ultimate quality of the resultingcoffee beans depends on the genetics of the plant, the soil in which it grows and the microclimate, whichencompasses factors such as altitude, the amount of rainfall and sunlight, and daily temperature fluctuations. Alongwith the roasting processes that are applied, these agricultural and geographical considerations are responsible forthe taste differences among the many varieties of coffee beans that suppliers combine to produce the variousdistinctive blends one can purchase (From Scientific American, June 2002).Exercise 3. Now read detailed explanation of the effects of caffeine provided by biologist Neal J.

Smatresk,Dean of the College of Science at the University of Texas at Arlington, and find answers to thesequestions:1. What is a neurotransmitter? What is a second messenger?2. How does caffeine affect heart?3. Does caffeine affect all animals?28How does caffeine affect the body?Caffeine--the drug that gives coffee and cola its kick--has a number of physiological effects. At the cellularlevel, caffeine blocks the action of a chemical called phosphodiesterase (PDE).

Inside cells, PDE normally breaksdown the second chemical messenger cyclic adenosine monophosphate (cAMP). Many hormones andneurotransmitters cannot cross the cell membrane, and so they exert their actions indirectly via such secondmessengers; when they bind to a receptor on the surface of a cell, it initiates a chemical chain reaction called anenzyme cascade that results in the formation of second messenger chemicals.Historically, cAMP was the first second messenger ever described. Now, however, scientists have identifiedseveral major classes of second messengers, which are generally formed in similar ways through a set ofmolecules called G proteins.

The advantage of such a complex system is that an extracellular signal can be greatlyamplified in the process, and so have a massive intracellular effect.Thus, when caffeine stops the breakdown of cAMP, its effects are prolonged, and the response throughoutthe body is effectively amplified. In the heart, this response prompts norepinephrine--also called noradrenalin--anda related neurotransmitter, epinephrine, to increase the rate and force of the muscle's contractions. Although thetwo act in concert, norepinephrine is released by sympathetic nerves near the pacemaker tissue of the heart,whereas epinephrine is released primarily by the adrenal glands.

These chemical messages lead to "fight or flight"behavior. During stressful or emergency conditions, they raise the rate and force of the heart, thereby increasingthe blood pressure and delivering more oxygen to the brain and other tissues.Caffeine would be expected to have this effect on any animals that used these neurotransmitters to regulatetheir heartbeat.

Generally speaking, the effects of caffeine are most pronounced in birds and mammals. Reptileshave some response, and lower vertebrates and invertebrates have rather small or no responses. From anevolutionary perspective, fish and amphibians don't show as strong a response to epinephrine and norepinephrineas the higher vertebrates, and they lack a well-developed sympathetic (that is, stimulatory) enervation to heart.Exercise 4.

What positive and negative effects produced by coffee do you know? Choose from the listbelow:a. Coffee boosts attention, concentration and alertness.b. Coffee improves mental performance.c. Coffee increases life expectancy.d. Coffee helps to fight infections.e. Coffee prevents aging.f. Coffee increases the risk of cardiovascular diseases.g. Coffee can lead to a stroke.h.

Coffee protects against cancer.Exercise 5. Read the article about health effects of coffee to check your answers in Exercise 4.Coffee as a Health Drink? Studies Find Some BenefitsBy Nickolas BakalarCoffee is not usually thought of as health food, but a number of recent studies suggest that it can be a highlybeneficial drink. Researchers have found strong evidence that coffee reduces the risk of several serious ailments,including diabetes, heart disease and cirrhosis of the liver.

Among them is a systematic review of studies publishedlast year in The Journal of the American Medical Association, which concluded that habitual coffee consumptionwas consistently associated with a lower risk of Type 2 diabetes. Exactly why is not known, but the authors offeredseveral explanations.Coffee contains antioxidants that help control the cell damage that can contribute to the development of thedisease. It is also a source of chlorogenic acid, which has been shown in animal experiments to reduce glucoseconcentrations. Caffeine, perhaps coffee’s most famous component, seems to have little to do with it; studies thatlooked at decaffeinated coffee alone found the same degree of risk reduction.Larger quantities of coffee seem to be especially helpful in diabetes prevention. In a report that combinedstatistical data from many studies, researchers found that people who drank four to six cups of coffee a day had a28 percent reduced risk compared with people who drank two or fewer.

Those who drank more than six had a 35percent risk reduction.Some studies show that cardiovascular risk also decreases with coffee consumption. Using data on morethan 27,000 women ages 55 to 69 in the Iowa Women’s Health Study who were followed for 15 years, Norwegianresearchers found that women who drank one to three cups a day reduced their risk of cardiovascular disease by24 percent compared with those drinking no coffee at all.

But as the quantity increased, the benefit decreased. Atmore than six cups a day, the risk was not significantly reduced. Still, after controlling for age, smoking and alcoholconsumption, women who drank one to five cups a day — caffeinated or decaffeinated — reduced their risk ofdeath from all causes during the study by 15 to 19 percent compared with those who drank none.29The findings, which appeared in May in The American Journal of Clinical Nutrition, suggest that antioxidantsin coffee may dampen inflammation, reducing the risk of disorders related to it, like cardiovascular disease. Severalcompounds in coffee may contribute to its antioxidant capacity, including phenols, volatile aroma compounds andoxazoles that are efficiently absorbed.

In another analysis, published in July in the same journal, researchers foundthat a typical serving of coffee contains more antioxidants than typical servings of grape juice, blueberries,raspberries and oranges. “We were surprised to learn that coffee quantitatively is the major contributor ofantioxidants in the diet both in Norway and in the U.S.A.,” said Rune Blomhoff, the senior author of both studiesand a professor of nutrition at the University of Oslo.The same anti-inflammatory properties may explain why coffee appears to decrease the risk of alcoholrelated cirrhosis and liver cancer.