Caffeine Caffeine is probably the mostwidely used drug in the world. Humans have been cons

Caffeine

Caffeine is probably the mostwidely used drug in the world. Humans have been consuming caffe-ine forhundreds of years. primarily in the form. of coffee, tea, and cocoa. Habitualcoffee and tea drinkers had long been observed to have a lower incidence ofnon-melanoma素瘤) skin cancers,although no one knew why. A recent study found thatcaffeine affects skin cells damaged by ultraviolet radiation, a main cause ofskin cancer. Caffeine interferes with a protein that cancerous cells need tosurvive, leaving the damaged cells to die before they become cancerous. Drinkingcaffeinated coffee has also beenassociated with a decreased incidence of endometrial(子宫内膜的) cancer-that is, cancer of the cells liningthe uterus-the strongest effect appears to be in overweight women, who are atgrea-test risk for the disease. Researchers believe blood sugar, fat cells, andestrogen (雌性激素) may play a role. Although the mechanism remains unknown, people whodrink more than two cups of coffee or tea a day reportedly have about half therisk of developing chronic liver disease as those who drink less than one cupof coffee daily; caffeinated coffee has also been associated with lowered riskof cirrhosis(肝硬化) and liver cancer.

While many of caffeine'sundesirable effects', such as elevated heart rate and blood pressure, arebrief, some short-term benefits, including pain relief, increased alertness,and increased physical en-durance, have also been attributed to caffeine. As acomponent of numerous over-the-counter diet pills and pain relievers, caffeineincreases their effectiveness and helps the body absorb them more quickly.Byconstricting (收缩) blood vessels in thebrain, it can alleviate headaches-evenmigraines (偏头痛)-and can helpcounter the drowsiness (眩晕) caused by antihistamines c抗组胺药).

Caffeine does not alter theneed for sleep, but it does offer a temporary solution to fatigue for peo-plewho need to stay alert. Research has shown that sleep-deprived individuals whoconsumed caffeine had improved memory and reasoning abilities, at least in theshort term. Studies of runners and cyclists have shown that caffeine canimprove their stamina-hence its addition to energy-boosting sports drinks.

People who consume a lot ofcaffeine regularly may develop temporary withdrawal symptoms,headache being themost common, if they quit or cut back on it abruptly. Fortunately, thesesymptoms last only a day or two in most cases. Individuals who are moresensitive to the stimulatory side effects of caffeine may want to avoid it, butmost doctors agree 'that the equivalent of three cups of coffee a day does notharm healthy people. There is no medical basis to give up daily caffeine andmany reasons to include a moderate amount in one's diet.

Drinking coffee or tea may help

A.lower the incidence of being overweight

B.lower the incidence of non-melanoma skin cance

C.increase the incidence of endometrial cancer

D.increase the incidence of liver cance