From VOA Learning English, this is Science in the News.

　　I'm Anna Matteo.

　　And I'm Christopher Cruise.

　　Today on the program, we explore the history of chocolate -- a favorite food for many people. Researchers have known for some time that chocolate is good for the heart. We will report on a study that shows why this is so. We also tell you about the health effects of dark chocolate.

　　The Tasty History of Chocolate

　　The history of chocolate begins with a plant whose scientific name -- Theobroma cacao -- means "food of the gods." For centuries, people have been enjoying the rich flavor of chocolate, a product made from this plant.

　　Historians believe the Mayan people of Central America first learned to farm cacao plants around 2,000 years ago. The Maya took the cacao trees from the rainforests and grew them around their homes. They cooked the cacao seeds, then crushed them into a soft paste. They mixed the paste with water and flavorful spices to make an unsweetened chocolate drink.

　　Cacao and chocolate were an important part of Maya culture. There are often images of cacao plants on Maya buildings and art objects. Ruling families drank chocolate at ceremonies. And, even poorer members of Mayan society could enjoy the drink once in a while. Historians believe that cacao seeds were also used in marriage ceremonies as a sign of the union between a husband and wife.

　　The Aztec culture in current-day Mexico also prized chocolate. But the cacao plant could not grow in the area where the Aztecs lived. So they traded to get cacao. They even used cacao seeds as a form of money to pay taxes or give as offerings to the gods.

　　Only the very wealthy people in Aztec societies could afford to drink chocolate because cacao was so valuable. The Aztec ruler Montezuma was believed to have drunk 50 cups of chocolate every day.

　　Some experts believe the word for chocolate came from the Aztec word "xocolatl," which means "bitter water" in the Nahuatl language. Others believe the word "chocolate" was created by combining Mayan and Nahuatl words.

　　The explorer Christopher Columbus brought cacao seeds to Spain after his trip to Central America in 1502. But it was the Spanish explorer Hernando Cortes who understood that chocolate could be a valuable investment. In 1519, Cortes arrived in Mexico. He believed the chocolate drink would become popular with Spaniards. After the Spanish soldiers defeated the Aztec empire, they were able to seize the supplies of cacao and send them home. Spain later began planting cacao in its colonies in the Americas in order to supply the large demand for chocolate.

　　The wealthy people of Spain first enjoyed a sweetened version of the chocolate drink. Later, the popularity of the drink spread throughout Europe. The English, Dutch and French began to plant cacao trees in their own colonies. Until the 18th century, only wealthy people could afford to drink chocolate. During the period known as the Industrial Revolution, new technologies helped make chocolate less costly to produce.

　　Farmers grow cacao trees in many countries in Africa, Central and South America. The trees grow in the shady areas of rainforests near the Earth's Equator. But these trees can be difficult to grow.

　　They require an exact amount of water, warmth, soil and protection. After about five years, cacao trees start producing large fruits called "pods," which grow near the trunk of the tree. The seeds inside this pod are harvested to make chocolate.

　　Growing cacao is very hard work for farmers. They sell their harvest on a futures market. This means that economic conditions beyond their control can affect the amount of money they will earn.

　　Today, chocolate industry officials, activists, and scientists are working with farmers. They are trying to make sure that cacao can be grown in a way that is fair to the farmers and safe for the environment.

　　To become chocolate, cacao seeds go through a long production process in a factory. Workers must sort, clean and cook the seeds. Then they break off the covering of the seeds so that only the inside fruit -- or nibs -- remain. Workers crush the nibs into a soft substance called chocolate liquor. This gets separated into cacao solids and a fat called cocoa butter.

　　Chocolate makers have their own special recipes in which they combine chocolate liquor with exact amounts of sugar, milk and cocoa fat. They finely crush this "crumb" mixture so it is smooth. The mixture then goes through two more processes before it is shaped into a mold form.

　　Chocolate making is a big business. Each year, the market value of the cacao crop around the world is more than five billion dollars. Chocolate is especially popular in Europe and the United States. Americans eat an average of more than five kilograms of chocolate per person every year. Specialty shops that sell costly chocolates are also very popular. Many offer chocolate lovers the chance to taste chocolates grown in different areas of the world.

　　Dark Chocolate and Heart Health

　　Researchers have known that chocolate -- especially dark chocolate -- is good for the heart. Now, they know why. Besides tasting good, researchers have found that dark chocolate protects against heart disease in two ways: it returns movement to hardening arteries. It also keeps white blood cells from gathering on blood vessel walls. Both of these conditions can lead to plaque formation. Plaque can block the flow of blood, causing heart disease.

　　Researchers from the Netherlands reported the findings. The Dutch researchers studied 44 middle-aged men who were considered overweight. The men ate 70 grams of both dark and milk chocolate every day over two periods of four weeks.

　　The heart-healthy substance in chocolate is an organic substance called flavanol. Flavanols are also found in vegetables, fruits and green tea.

　　Gerald Weissmann is with the FASEB Journal, which published the study findings earlier this year. He says the researchers found that there is something about the flavanols in dark chocolate that makes people like it more than milk chocolate.

　　"In this controlled study -- the first time it's ever been done -- they gave the same amount of flavanol in dark chocolate and regular chocolate. And lo and behold, the men didn't have different amounts of flavanols in the diet. But they ate more of the dark chocolate one because they liked it better."

　　Mr. Weissman says researchers asked the men in the study to talk about the smell and taste of dark chocolate.

　　"So, the taste component or psychological component of dark chocolate improved, number one, the elasticity and response of the arteries to blood flow, number two, the way that neutrophils -- white cells -- stick to the lining of blood vessels and number three, markers of inflammation."

　　And knowing it was good for the heart seemed to make the men feel less guilty about eating it.

　　Researchers may someday develop a treatment that has the same health benefits as dark chocolate. But even if they do, we are sure that eating a piece of dark chocolate will still be more fun.

　　Scientists to Study Health Benefits of Chocolate

　　Dark chocolate has been shown to help prevent heart disease. But eating too much of it may cause people to gain weight. Now, scientists are looking for a way to put dark chocolate's helpful ingredients -- or parts -- into pills. That way, we can get the benefits of dark chocolate, but not the weight gain.

　　Cacao has flavanols that may help reduce the risk of heart attack or stroke. These chemicals may lower blood pressure and cholesterol levels, and improve the body's use of insulin. Insulin helps control the amount of glucose or sugar in the blood.

　　Steve Koumanelis is a chocolatier. He makes and sells chocolate treats in Washington, D.C. He says dark chocolate is an increasingly popular product.

　　"A lot of people are gravitating towards dark chocolate because they just decide they love it, and they also have been reading all about the health benefits of dark chocolate."

　　But those health benefits have yet to be confirmed in studies involving large numbers of people. Also, during the manufacture of chocolate, many flavanoids are destroyed, while sugar and fats are added to make the chocolate taste better.

　　Scientists want to learn the benefits of flavanols before they are changed in the manufacturing process. They have announced plans for a four-year-long study of 18,000 adults. The subjects will take small amounts of pure cacao flavanols. The study is believed to be the largest of its kind.

　　Jo-Ann Manson works at Brigham and Women's Hospital in Boston, Massachusetts. She is the lead researcher in the study.

　　"This capsule of cocoa flavanols will avoid having the calories and the sugar and the saturated fat found in chocolate."

　　And the flavanols will not have any taste.

　　The subjects in the new study are to be separated into two groups. Members of one group will take pills containing flavanols. The other group will take "placebo" pills -- substances that do not have anything in them, other than, perhaps, sugar.

　　Whatever the result of the study, chocolatier Steve Koumanelis is not worried about his business.

　　"People like the experience of actually biting into a piece of chocolate, whatever their favorites are."

　　The flavanol benefits test is just starting. For now, people will have to get their flavanols the tasty way -- by eating dark chocolate!

　　This Science in the News was written by Dana Demange and Christopher Cruise, who also produced the program.

　　I'm Anna Matteo.

　　And I'm Christopher Cruise.

　　Join us again next week for more news about science on the Voice of America.