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 tell about some health problems linked to extreme heat. We also tell about what to do to prevent and treat these problems.

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VOICE ONE:

Extremely hot weather is common in many parts of the world. Although hot weather just makes most people hot, it can cause medical problems -- and death.

Floods, storms and other natural events kill thousands of people every year. And, as expected, we hear much about them in news reports. We generally hear little, however, about what experts say may be nature's deadliest killer -- heat.

Health experts say that between nineteen seventy-nine and nineteen ninety-nine, extremely hot weather killed more than eight thousand people in the United States. In that period, more Americans died from extreme heat than from severe storms, lightning, floods and earthquakes together. And in nineteen ninety-five, more than six hundred people died in a period of extremely hot weather in one city -- Chicago, Illinois.

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To measure extreme heat, weather experts have developed the Mean Heat Index. It measures the average of how it felt all day on an extremely hot day.

Experts say it is the total heat of a hot day or several hot days that can affect health. Several hot days are considered a heat wave. Experts say heat waves often become deadly when the nighttime temperature does not drop much from the highest daytime temperature. This causes intense stress on the human body.

Doctors say people can do many things to protect themselves from the dangers of extreme heat. Stay out of the sun, if possible. Drink lots of cool water. Wear light-colored clothing made of natural materials. Make sure the clothing is loose, permitting freedom of movement. And learn the danger signs of the medical problems that are linked to heat.

VOICE ONE:

The most common medical problem caused by hot weather is heat stress. Usually, it also is the least severe. The causes of heat stress include physical work or exercise, heavy clothes, hot weather or high humidity. Humidity is the amount of water in the air.

Several of these conditions together can raise a person's body temperature above safe limits. The person perspires heavily, losing large amounts of body water and salt.

For most people, the only result of heat stress is muscle pain. The pain is a warning that the body is becoming too hot. Doctors say drinking water will help the pain disappear after the body again has the right amounts of water and salt. For some people, however, the result is more serious. For people who are not in good health, heat can make an existing medical problem worse.

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For example, doctors say some people face a greatly increased danger from heat stress. These people have a weak or damaged heart, high blood pressure, or other problems of the blood system. Severe heat can help cause a heart attack or stroke. Health experts say this is the most common cause of death linked to hot weather.

Doctors also say severe heat increases problems for small children, older people and people suffering from the disease diabetes. It also is bad for people who weigh too much and have too much body fat, and for people who drink alcohol. Hot weather also increases dangers for people who must take medicine for high blood pressure, poor blood flow, nervousness or depression.

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VOICE ONE:

If heat stress is not treated, it can lead to a more serious problem called heat exhaustion. Perspiration is one of the body's defenses against heat. That is how the body releases water to cool the skin. However, a person suffering from heat exhaustion loses too much water through perspiration. The person becomes dehydrated.

Dehydration limits a person's ability to work and think. Experts say a reduction of only four or five percent in body water leads to a drop of twenty to thirty percent in work ability. The loss of salt through perspiration also reduces the amount of work that muscles can do.

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A person suffering from heat exhaustion feels weak and extremely tired. He or she may have trouble walking normally. Heat exhaustion also may produce a general feeling of sickness, a fast heartbeat, breathing problems, and pain in the head, chest or stomach. Doctors say people suffering from these problems should move to a cool place and drink water.

Heat exhaustion can develop quickly. But it also can develop slowly, over several days. Doctors call this disorder dehydration exhaustion. Each day, a person's body loses only a little more water than is taken in. The person may not even know the problem is developing. But if the problem continues for several days, the effects will be the same as the usual kind of heat exhaustion. The treatment for dehydration exhaustion is the same as for heat exhaustion. Drink large amounts of water, and rest in a cool place.

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VOICE ONE:

Heat exhaustion can lead to heat stroke if it is not treated. With heat stroke, the body temperature rises to more than forty degrees Celsius.

The body stops perspiring. And the skin becomes dry and very hot. A person may even become unconscious, not knowing what is happening.

Doctors say the body's tissues and organs begin to cook when body temperature is higher than forty-two degrees Celsius. Permanent brain damage and death may result. Immediate medical help is necessary for someone with heat stroke. Doctors say immediate treatment is necessary or the person could die before help arrives.

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Immediate treatment should begin by moving the victim out of the sun. Raise the person's feet up about thirty centimeters. Then, take off the person's clothing. Put water on the body. And place pieces of ice in areas where blood passageways are close to the skin. These areas include the back of the neck and under the arms. The purpose is to cool the victim as quickly as possible to stop the body's temperature from increasing.

Experts say it is important to know the danger signs of each of the medical disorders linked to hot weather. And they say you should know what to do if the signs appear.

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VOICE ONE:

Experts say water is important for many health reasons. The body itself is mostly water -- more than sixty-five percent water. Water in blood carries hormones and antibodies through the body. Water in urine carries away waste materials. Water is also needed for cooling the body on hot days, and when we are working or exercising. Water carries body heat to the surface of the skin. There, the heat is lost through perspiration.

Health experts say adults should drink about two liters of water each day to replace all the body water lost in liquid wastes and perspiration. They say people should drink more than that in hot weather.

Experts say it is especially important to drink before, during and after exercise. They say we should drink water even before we start to feel like we need something to drink. This is because we sometimes do not feel thirsty until we already have lost a lot of body liquid.

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In hot weather, drinking cold liquids is best. They do more than just replace lost body water. Cold liquids also help cool us faster than warm liquids. This is because they take up more heat inside the body and carry it away faster.

Yet experts say that sweet drinks are not good to drink in hot weather. The sugar slows the liquid from getting into the blood system. Tea and coffee also are not effective. Doctors also warn against alcoholic drinks. Alcohol speeds the loss of body water through liquid wastes.

VOICE ONE:

In addition to drinking cool water, doctors say there are other things that can protect against the health dangers of heat. Stay out of the sun, if possible. Wear loose, lightweight and light-colored clothes. Wear a hat or other head cover while in the sun. Eat fewer hot and heavy foods. If possible, cook foods during cooler times of the day. Also, rest more often. Physical activity produces body heat.

Experts say these simple steps can prevent the dangerous health problems linked to heat. They will prevent sickness, help you feel better and may even save your life.

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VOICE TWO:

This SCIENCE IN THE NEWS program was written by Oliver Chanler and Nancy Steinbach. It was produced by Brianna Blake. I'm Faith Lapidus.

VOICE ONE:

And I'm Bob Doughty. Join us again next week for more news about science, in Special English, on the Voice of America.