BOB DOUGHTY: This is SCIENCE IN THE NEWS in VOA Special English. I'm Bob Doughty.

FAITH LAPIDUS: And I'm Faith Lapidus. This week, we will tell the story of aspirin.

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BOB DOUGHTY: People have known since ancient times that aspirin lessens pain and lowers high body temperature. But that is not all the drug can do. It has gained important new uses in recent years. Small amounts may help prevent a stroke or heart attack. Some researchers say aspirin may help patients with colon cancer live longer, or may even prevent some cancers.

But doctors also warn that the acid in aspirin can cause problems like bleeding in the stomach and intestines.

FAITH LAPIDUS: So, how did aspirin become so important? The story begins with a willow tree. 2,000 years ago, the Greek doctor Hippocrates advised his patients to chew on the bark and leaves of the willow.

The tree contains a chemical called salicin. In the 1800s, researchers discovered how to make salicylic acid from the chemical. In 1897, a chemist named Felix Hoffmann at Friedrich Bayer and Company in Germany created acetyl salicylic acid.

Later, it became the active substance in a medicine that Bayer called aspirin. The "a" came from acetyl. The "spir" came from the spirea plant, which also produces salicin. And the "in"? That is a common way to end medicine names.

BOB DOUGHTY: In 1982, a British scientist shared the Nobel Prize in Medicine in part for discovering how aspirin works. Sir John Vane found that aspirin blocks the body from making natural substances called prostaglandins.

Prostaglandins have several effects on the body. Some cause pain and the expansion, or swelling, of damaged tissue. Others protect the lining of the stomach and small intestine.

Prostaglandins also make the heart, kidneys and blood vessels work well. But there is a problem. Aspirin works against all prostaglandins, good and bad.

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FAITH LAPIDUS: Scientists have also learned how aspirin interferes with an enzyme. One form of this enzyme makes the prostaglandin that causes pain and swelling. Another form of the enzyme creates a protective effect. So aspirin can reduce pain and swelling in damaged tissues. But it can also harm the inside of the stomach and small intestine. And sometimes it can cause bleeding.

But a British study released in 2009 suggests that taking another drug with a small amount of aspirin may help reduce the risk of bleeding. If that proves true, it would help thousands of people who are seeking to prevent life-threatening conditions.

BOB DOUGHTY: Many people take aspirin to reduce the risk of a heart attack or stroke from blood clots. Clots can block the flow of blood to the heart or brain and cause a heart attack or stroke. Scientists say aspirin prevents blood cells called platelets from sticking together to form clots.

A California doctor named Lawrence Craven first noted this effect 60 years ago. He observed unusual bleeding in children who chewed on an aspirin product to ease the pain after a common operation.

Doctor Craven believed that the bleeding took place because aspirin prevented blood from thickening. He thought this effect might help prevent heart attacks caused by blood clots.

He examined the medical records of 8,000 aspirin users and found no heart attacks in this group. He invited other scientists to test his ideas. But it was years before large studies took place.

FAITH LAPIDUS: Charles Hennekens of Harvard Medical School led one of the studies. In 1983, he began to study more than 22,000 healthy male doctors over 40 years of age. Half took an aspirin every other day. The others took what they thought was aspirin. But it was only a placebo, a harmless substance.

Five years later, Doctor Hennekens reported that people who took aspirin reduced their risk of a heart attack. But they had a higher risk of bleeding in the brain than the other doctors.

BOB DOUGHTY: Last year, a group of experts examined studies of aspirin at the request of federal health officials in the United States. The experts said people with an increased risk of a heart attack should take a low-strength aspirin every day.

Aspirin may help someone who is having a heart attack caused by a blockage in a blood vessel. Aspirin thins the blood, so it may be able to flow past the blockage. But heart experts say people should seek emergency help immediately. And they say an aspirin is no substitute treatment, only for temporary help.

FAITH LAPIDUS: But what about reducing pain? Aspirin competes with many other medicines for reducing pain and high body temperature. The competition includes acetaminophen, the active substance in products like Tylenol. Like the medicine ibuprofen, aspirin is an NSAID -- a non-steroidal anti-inflammatory drug.

Several studies have found that men who take aspirin and other NSAIDS have a decreased risk of prostate cancer. The prostate is part of the male reproductive system.

BOB DOUGHTY: Researchers at the Mayo Clinic in Minnesota wanted to see how NSAIDs might affect prostates that are enlarged but not cancerous. They followed the health of 2,500 men for 12 years.

The researchers said these drugs may delay or stop development of an enlarged prostate. They said the risk of an enlarged prostate was 50 percent lower in the NSAID users than the other men. The risk of bladder problems was 35 percent lower.

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FAITH LAPIDUS: Other studies have suggested that aspirin can help with cancer prevention and survival. They showed that aspirin may help prevent cancers of the stomach, intestines and colon.

Researchers reported in 2009 about people who had colorectal cancer. They found that aspirin users had an almost 30 percent lower risk of dying from their cancer. That was during an average of 11 years after the cancer was discovered.

BOB DOUGHTY: Two years ago, European researchers reported that aspirin may have what they called a "long-term protective effect against colorectal cancer." Peter Rothwell of the University of Oxford led the researchers. They examined 20 years of results from four large studies.

The studies involved 14,000 people. Some of them took a 75 milligram baby aspirin once a day. Others took a 300 milligram, adult-sized aspirin.

The researchers found that people who took one aspirin a day for about six years reduced their risk of colon cancer by 24 percent. And deaths from the disease dropped by 35 percent. That was in comparison to those who took a harmless substance or nothing at all.

FAITH LAPIDUS: Last week, the Lancet published the combined results of a larger observational study, also led by Professor Rothwell. This time, he and researchers examined eight studies that involved more than 25,000 individuals.

They found that taking a small aspirin once a day reduced death rates from a number of common cancers. Taking 75 milligrams of aspirin daily for five years reduced the risk of bowel cancer by one-fourth. Deaths from the disease fell by one-third.

BOB DOUGHTY: Aspirin does not help everything, however. It can cause problems. For example, it can interfere with other medicines, although this is true of many drugs. Also, some people should not take aspirin. People who take other blood thinners or have bleeding disorders are among this group. Pregnant women are usually told to avoid aspirin.

And research has shown a link between aspirin use and the disease Reye's syndrome. Children's doctors say patients up to age 19 should not take anything containing salicylatic products when sick with high temperatures.

FAITH LAPIDUS: Experts say most people should not take aspirin for disease prevention without first talking to a doctor because there are risks to taking aspirin. Some researchers have even said that some people get little or no protection from aspirin. So research continues on one of the oldest and most widely used drugs in the world.

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BOB DOUGHTY: This SCIENCE IN THE NEWS was written by Jerilyn Watson and Christopher Cruise. Our producer was June Simms. I'm Bob Doughty.

FAITH LAPIDUS: And I'm Faith Lapidus. Join us again next week for more news about science in Special English on the Voice of America.

intestine: the whole alimentary canal from the mouth downward 肠

salicin: a bitter compound present in willow bark. It is a glucoside related to aspirin, and accounts for the ancient use of willow bark as a pain-relieving drug. 水杨苷

acetyl salicylic acid: 乙酰水杨酸

spirea: a shrub of the rose family, with clusters of small white or pink flowers 绣线菊

prostaglandin: 前列腺素

platelet: a very small blood cell, shaped like a disc. Platelets help to clot the blood when a person bleeds. 血小板

placebo: a substance that has no physical effects, given to patients who do not need medicine but think that they do, or used when testing new drugs （给无实际治疗需要者的）安慰剂；（试验药物用的）无效对照剂

acetaminophen: 对乙酰氨基酚

ibuprofen: a drug used to reduce pain and inflammation 布洛芬，异丁苯丙酸（镇痛消炎药）

Reye's syndrome: a life-threatening metabolic disorder in young children, of uncertain cause but sometimes precipitated by aspirin and involving encephalitis and liver failure 雷氏症候群

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（来源：VOA 编辑：崔旭燕）