VOA慢速英语20061212b

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This is SCIENCE IN THE NEWS, in VOA Special English. I'm Steve Ember.

VOICE TWO:

And I'm Barbara Klein. This week -- the story of aspirin 1.

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Our story begins with the willow 2 tree. Since ancient times, people have known about its ability to reduce pain and high body temperature. More than two thousand 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. From salicin, researchers in the eighteen hundreds discovered how to make salicylic acid. And in eighteen ninety-seven, a chemist named Felix Hoffmann at Friedrich Bayer and Company in Germany created acetyl salicylic acid.

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


Aspirin

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In nineteen eighty-two, 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 4, of damaged tissue. Others protect the lining 5 of the stomach and small intestine 6.

Prostaglandins also make the heart, kidneys and blood vessels 7 work well. But there is a problem. Aspirin works against all prostaglandins, good and bad.

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Scientists learned how aspirin interferes 9 with an enzyme 10. 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.

Today, aspirin competes with a lot of other medicines for headaches, muscle pain and fever. These include acetaminophen, the active substance in products like Tylenol.

But many people take aspirin to reduce the risk of a heart attack or stroke from blood clots 11. 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 12 this effect more than fifty years ago. He observed unusual bleeding in children who chewed on an aspirin product to ease the pain after a common throat operation.

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

He examined the medical records of eight thousand 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.

Charles Hennekens of Harvard Medical School led one of the studies. In nineteen eighty-three, he began to study more than twenty-two thousand healthy male doctors over forty years of age. Half took an aspirin every other day. The others took what they thought was aspirin. It was only a placebo 13, an inactive substance.

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

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More recently, 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.

People who are most likely to suffer a heart attack include men over forty and women over fifty. People who are overweight or smoke are also at greater risk. So are people with heart disease, diabetes 14, high blood pressure or high cholesterol 15.

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In two thousand five, scientists reported the results of a major study that confirmed that aspirin also helps women. But the results were surprising. The study found that aspirin did not reduce the risk of a first heart attack in women.

But women who took aspirin were seventeen percent less likely to have a stroke than women who took a placebo. And they were twenty-four percent less likely to have the most common form of stroke. The effects were greatest in women sixty-five years of age and older.

The results were the opposite of what doctors see in men.

The study lasted ten years. It involved forty thousand women age forty-five to eighty. The women who took aspirin were given one hundred milligrams every other day.

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Aspirin may help someone who is having a heart attack caused by a blockage 16 in an artery 17. Aspirin thins the blood, so it may be able to flow past the blockage. But heart experts say people should seek emergency help immediately. They say an aspirin is no substitute for treatment.

And some people should not take aspirin. These include people who take other blood thinners or have bleeding disorders 18. Pregnant women are usually told to avoid aspirin. And children who take aspirin can suffer a disease called Reye's syndrome 19.

Aspirin can also interfere 8 with other medicines, although this is true of many drugs.

A well-known risk of aspirin is stomach bleeding. Acid in the drug can damage the tissue of the stomach or intestines 20. Yet some studies have found that aspirin may help prevent cancers of the stomach, intestines and colon 21.

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A recent study found that aspirin blocks the formation of blood vessels that feed the growth of cancer. Researchers at Newcastle University in England explored a biological process that makes blood vessels grow. The researchers studied how aspirin affects the cells found on the inner surface of blood vessels. They found that a small amount of aspirin suppressed the way the cells form tubes.

But lead researcher Helen Arthur says people with cancer should not take aspirin unless they are advised to do so by a doctor. She warns that large amounts of aspirin over a long period can cause severe stomach bleeding and death.

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Aspirin is one of a group of medicines known as NSAIDs [EN-sayds] -- non-steroidal anti-inflammatory drugs. Another example is ibuprofen.

Several studies have found that men who take NSAIDS have a decreased risk of prostate cancer. 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 two thousand five hundred men for twelve years. One-third were taking NSAIDs daily when they entered the study.

The scientists recently announced that these drugs may delay or prevent the development of an enlarged prostate. They said the risk of an enlarged prostate was fifty percent lower in the NSAID users than the other men. And the risk of bladder problems was thirty-five percent lower.

The prostate gland 3 is part of the male reproductive system and is just below the bladder. Growth of the prostate is common as men get older. It can mean repeated visits to the bathroom and other effects on a man's quality of life.

But the scientists say that because of risks like stomach bleeding, they are not advising all men to take aspirin. If men are taking it already, they say, then the findings suggest another way it might help. The reasons are not clear, though, and the findings must be reproduced by other studies

Most of the men were taking aspirin. But the study found that other kinds of NSAIDs appeared to have the same effect. And the amount taken did not seem to make much difference either.

In any case, medical experts say people should not take aspirin for disease prevention without first talking to a doctor. There are risks, and researchers have reported that some people get little or no protection from aspirin. But medical research continues to give new life to one of the oldest and most widely used drugs in the world.

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SCIENCE IN THE NEWS was written by George Grow and produced by Brianna Blake. For more science news, and MP3 files and transcripts 22 of our programs, go to www.unsv.com. I'm Barbara Klein.

VOICE ONE:

And I'm Steve Ember. We hope you can join us again next week for more news about science in Special English on the Voice of America.