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This is SCIENCE IN THE NEWS, in VOA Special English. I'm Barbara Klein.

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And I'm Bob Doughty. On our program today, we tell about aspirin. It is one of the most widely used medicines in the world. We also tell about some recent studies involving aspirin.

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More than two thousand years ago, the Greek doctor Hippocrates advised his patients about a way to ease pain. He told them to bite, or chew, on the bark of the willow tree. The outer covering of the tree contains a chemical called salicylic acid.

By the seventeen hundreds, people used willow bark to reduce high body temperatures. In eighteen ninety-seven, a research scientist at the Bayer Company in Germany created acetyl salicylic acid. The company called the product aspirin, from the spirea plant, which also contains the chemical.

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Aspirin has been sold for more than a century as a treatment for high body temperatures, headaches and muscle pain. 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, 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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Scientists 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 the 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 pain medicines. Many people like to take acetaminophen instead. This is the active substance in products like Tylenol. Still, experts say aspirin does some things that the others cannot.

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

The use of aspirin to reduce the risk of heart disease has grown in recent years. One doctor first noted this effect in the nineteen-fifties.

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The doctor was Lawrence Craven. He observed unusual bleeding among children who chewed on aspirin gum to ease pain after a throat operation. Doctor Craven believed they were bleeding because aspirin prevented the blood from thickening. He decided that aspirin might help prevent heart attacks caused by blood clots.

So Doctor Craven examined medical records of about eight thousand people. He found no heart attacks or strokes among those who often used aspirin. Doctor Craven invited other scientists to test his ideas. But it was many years before large studies took place.

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Charles Hennekens of the 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 the doctors in the study took an aspirin every other day. The other half took what they thought was aspirin, but was just a harmless substance, or placebo.

Five years later, Doctor Hennekens reported that the men who took aspirin reduced their chances of a heart attack. However, the men who took aspirin also had a higher risk of bleeding in the brain.

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In recent years, a group of American medical experts examined studies on aspirin for the Department of Health and Human Services. The experts said people who have an increased risk of a heart attack should take a small amount of aspirin every day.

People who are most likely to suffer a heart attack include men over the age of forty and women over the age of fifty. People who weigh too much or smoke cigarettes also are at greater risk. So are people with diabetes, heart disease, high blood pressure or high levels of cholesterol in the blood.

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A major study in two thousand five confirmed that aspirin can also help women. Julie Buring of Brigham and Women's Hospital in Boston, Massachusetts, led the study. She said that among apparently health people, aspirin reduces the risk of heart attack in men. But for women it appears to reduce the risk of stroke.

The New England Journal of Medicine reported the findings. The study lasted ten years. It involved forty thousand women age forty-five and older. Those who received aspirin took one hundred milligrams every other day. The others took a placebo.

The study found that the women who took aspirin were seventeen percent less likely to have a stroke than the other women. The aspirin group also had a twenty-four percent lower risk for the most common form of stroke. This is caused by a clot in a blood vessel that carries blood to the brain.

The study found that aspirin had an even greater effect in women sixty-five years of age and older. Those who took aspirin were thirty percent less likely to have a stroke caused by a blood clot. They were also less likely to suffer a heart attack than those given a placebo.

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Aspirin may help someone who is having a heart attack caused by a blockage in the flow of blood to the heart. Aspirin thins the blood. This can permit blood to flow past the blockage in the artery.

But heart experts say people should seek emergency help immediately. They say an aspirin is no substitute for treatment. Some people should not take aspirin. These include people who take other blood thinners or have bleeding disorders.

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Like other medicines, aspirin can cause problems, especially if taken in large amounts. Acid in the drug may damage the tissue of the stomach or intestines. Aspirin can also interfere with the healing of cells. Some people develop severe bleeding.

Yet other studies have found that aspirin may help prevent cancers of the stomach, intestines and colon. Studies in the past twenty years showed that people who take aspirin have unusually low rates of such cancers. For example, a study published in two thousand five showed that long-term use of aspirin helps reduce the risk of colon cancer. However, the amount of aspirin required for this protective effect also could cause serious bleeding in the stomach or intestines.

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Another recent report about aspirin involves the most common form of breast cancer. In two thousand four, researchers announced findings from a study of almost three thousand women in New York City. The Journal of the American Medical Association published the findings.

The study compared women who took aspirin several times a week to women who did not. Scientists from Columbia University said the aspirin users had a twenty-five percent lower rate of breast cancer.

One doctor involved in the study said aspirin appeared to reduce the production of the female hormone estrogen. Estrogen is linked to up to seventy percent of all cases of breast cancer. But the scientists said they were not ready to advise women to take aspirin in hopes of protection against breast cancer.

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Doctors often do advise aspirin for patients at risk of diseases that result from blood clots, such as a heart attack. However, in two thousand four, a Harvard Medical School publication said that some people get little or no protection from aspirin.

In any case, medical experts say no one should take aspirin for disease prevention without first asking a doctor. Aspirin is sold in different strengths. It can interfere with other drugs. It also is not safe for everyone. Most pregnant women are told to avoid aspirin. Children who take aspirin can suffer from a disease called Reye's syndrome. Yet even with its problems, aspirin, remains one of the oldest, least costly and most widely used drugs in the world.

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VOICE ONE:

This SCIENCE IN THE NEWS program was written by George Grow and produced by Cynthia Kirk. I'm Barbara Klein.

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And I'm Bob Doughty. Join us again next week for more news about science in VOA Special English.