VOA慢速英语-SCIENCE IN THE NEWS - Ten Percent of Healthy People（在线收听）

VOICE ONE:

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

VOICE TWO:

And I'm Faith Lapidus. This week, we will tell about a brain injury known as silent stroke. We will also tell about melanoma -- the most deadly form of skin cancer. And, we will tell you about the healthful effects of vitamin D.

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Magnetic resonance imaging tests are used to inspect for damaged brain tissue and signs of stroke

Stroke is a serious problem that can lead to death. Usually the warning signs appear suddenly. But a recent study found that seemingly healthy middle-aged people could suffer a stroke without immediately knowing it. The finding was reported in "Stroke: Journal of the American Heart Association."

The study involved about two thousand people. They were the children of men and women who took part in the Framingham Heart Study. The Framingham Heart Study began sixty years ago in Framingham, a town in the American state of Massachusetts. Much of what doctors know about heart disease has resulted from this research project.

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The average age of men and women in the new study was sixty-two years. The group's members received medical examinations every four to eight years. They were given magnetic resonance imaging tests to inspect for damaged brain tissue and signs of stroke.

The imaging tests showed that nearly eleven percent of those with no sign of stroke had suffered a silent cerebral infarction, or silent stroke. Silent strokes are brain injuries likely caused by a blockage that limits blood to the brain.

Eighty-four percent of those who suffered silent strokes had a single wound, or lesion, in the brain. This kind of damage can lead to increased risk of future strokes and long-term memory loss.

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For the first time, the researchers found a link between silent stroke and the condition atrial fibrillation. Atrial fibrillation is the most common cause of unusual heartbeat in older adults.

Sudha Seshadri works at the Boston University School of Medicine. She says atrial fibrillation increased the risk of suffering a stroke more than two times. High blood pressure and systolic blood pressure were also linked to an increased risk of silent stroke. Blood pressure readings are usually given in two numbers. The upper number is systolic blood pressure.

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Doctor Seshadri says the findings show the need for early testing and treatment of conditions that could lead to heart disease in middle-aged people. Experts say nothing special needs to be done to reduce the risk of silent stroke. But they are urging people to watch for risk factors. They include atrial fibrilation, high blood pressure, heart disease, diabetes and cigarette smoking.

The American Stroke Association says people who think they are having a stroke should seek emergency medical help. The warning signs include sudden weakness, especially on one side of the body, and difficulty speaking or understanding. Other warning signs are trouble seeing in one or both eyes, trouble walking, loss of balance and severe head pain.

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An American study shows that increasing numbers of young women are developing melanoma, the most deadly form of skin cancer. The study did not identify causes of the increase. However, the lead researcher says it could be the result of young women seeking to make their skin darker.

The American Cancer Society says about sixty-two thousand cases of melanoma are found each year in the United States. The disease will kill more than eight thousand four hundred Americans this year.

The biggest risk for developing melanoma is ultraviolet radiation. However, genetics could also be important. People with light or fair skin are most at risk. Yet melanoma affects people of all races and skin colors.

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Results of the new study were reported last month in the Journal of Investigative Dermatology. The increase in melanoma cases is nothing new. Other studies have shown the rate of new cases increasing in the general population. But federal researchers did not know about the sharp increase among young women.

Mark Purdue of the National Cancer Institute led the study. His team examined rates of melanoma for a thirty-year period -- from nineteen seventy-three to two thousand four. They found more than twenty thousand melanoma cases in Americans between the ages of fifteen and thirty-nine years.

The researchers say they found that the rate among young women rose fifty percent since nineteen eighty. For men of the same age, however, the rate stayed the same.

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One reason for the rise in cases could be an increase in early discovery of the disease. But the researchers believe that is not the only reason because more serious forms of the cancer are being found.

Some experts say the study's results could be a sign of an even greater problem in the future. This is because melanoma can develop over years and become deadly later in life. The number of older adults with the disease has been increasing for many years.

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Mark Purdue says the findings suggest that public education campaigns about the dangers of skin cancer do not seem to be helping. He believes the increase may be connected to women spending more time under the sun and in tanning salon beds. Tanning beds produce ultraviolet radiation that can damage the skin.

The tanning salon industry disputes the idea that its treatments are to blame for the rising melanoma rates.

People can reduce their risk of developing the disease by avoiding the sun when it is strongest. Wearing protective clothing and sunblock products can also reduce the risk.

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Vitamin D helps bones and muscles grow strong and healthy. Low levels of vitamin D can lead to problems such as rickets, a disorder mainly found in children. Osteoporosis, the thinning of bone, is a common problem as people, especially women, get older. But more and more research is suggesting that vitamin D might also help prevent many diseases.

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The easiest way to get vitamin D is from sunlight. The sun's ultraviolet radiation reacts with skin cells to produce vitamin D. But many people worry about getting skin cancer and skin damage from the sun. As a result, they cover their skin, wear sunblock products or stay out of the sun.

Also, darker skinned people produce less vitamin D than lighter skinned people. Production also decreases in older people and those living in northern areas that get less sunlight.

Not many foods naturally contain vitamin D. Foods high in this vitamin include fish liver oils and oily fish such as salmon, tuna and mackerel.

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Boston University researchers reported last year that farmed salmon had only about one-fourth as much vitamin D as wild salmon.

Small amounts of the vitamin are found in beef liver, cheese and egg yolks. And some people take dietary supplements containing it. But most of the vitamin D in the American diet comes from foods with D added, like milk.

In nineteen ninety-seven, the United States Institute of Medicine established levels for how much vitamin D healthy people need. It set the daily amount at two hundred international units from birth through age fifty. It set the level at four hundred I.U.s through age seventy, and six hundred for age seventy-one and over.

But some groups say these amounts are not high enough. They are hoping that the new study findings will lead to new suggestions.

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Research in the past several years has shown that low levels of vitamin D may increase the risk of heart attacks in men and deaths from some cancers. Other studies have shown that people with rheumatic diseases often have low levels of vitamin D.

More doctors are now having their patients tested for their vitamin D levels. But as research continues, some experts worry that if people take too much vitamin D, it might act as a poison. Also, skin doctors warn people to be careful with sun exposure because of the risk of skin cancer.

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VOICE ONE:

This SCIENCE IN THE NEWS program was written by Lawan Davis, Caty Weaver and Brianna Blake, who also was our producer. I'm Bob Doughty.

VOICE TWO:

And I'm Faith Lapidus. Read and listen to our programs at voaspecialenglish.com. Join us at this time next week for more news about science on the Voice of America.