If you are taking vitamin supplements to reduce your risk of heart disease or cancer, a group of health experts want you to know that those vitamins may actually increase your risk of cancer.

The US Preventive Services Task Force came to this conclusion after reviewing dozens of studies. Nearly half of adults in the US take at least one vitamin or mineral supplement on a regular basis. These pills are advertised as a way to promote general health. In some cases, producers promote them as cancer fighters and heart protectors.

    Studies in animals and in laboratory dishes suggest that oxidative(氧化性的) stress contributes to diseases like cancer and heart disease. If so, there is a reason to believe that antioxidants—including beta－carotene, vitamins A, C, and E—could be useful as preventive medicines.

    But when the Task Force examined the medical evidence on vitamins, it found "inadequate(不充分的) evidence" to support the claims that vitamin and mineral supplements benefit healthy adults.

    "Cardiovascular(心血管的) disease and cancer have a significant health impact in America, and we all want to find ways to prevent these diseases，" Dr. Virginia Moyer, who heads the Task Force, said in a statement. But so far, she added, the medical evidence does not show that taking vitamins is helpful in this aspect.

    However, the Task Force did find "adequate evidence" that people with a raised risk for lung cancer actually increase their risk further by taking beta－carotene, a precursor of vitamin A.

The Task Force recommendations of taking vitamins regularly apply to healthy adults aged 50 and older who don't have "special nutritional needs". The advice does not apply to children, women who are pregnant or may become pregnant, people with chronic illnesses, or people who have to take supplements because they can't get all their essential nutrients from their diet.

    Are you preparing for a big test? If so, you may want to go to play some basketball in between hitting the books. Doctors are starting to find more and more information that suggests a connection between exercise and brain development. Judy Cameron, a scientist at Oregon Health and Science University, studies brain development. According to her research, it seems that exercise can make blood vessels, including those in the brain, stronger and more fully developed. Dr. Cameron is sure that this allows people who exercise to think better. As she says, "While we already know that exercise is good for the heart, exercise can actually cause physical changes in the brain."

    The effects of exercise on brain development can even be seen in babies. Babies who do activities that require a lot of movement show greater brain development than babies who are less physically active. Even a little movement can show big results. Margaret Barnes, a scientist, also believes in the importance of exercise. She thinks that many learning disabilities that children have in primary school or high school can result from a lack of movement as babies. Babies need movement that encourages and excites their five senses. They need to set up a connection between motion and memory. In this way, as they get older, children will begin to connect physical activity with higher learning," says Margaret.

    Older people can develop their brains as well. Cornell University studied a group of seniors who have a short-term memory increase of up to 40 percent after exercising just three hours a week. The exercise does not have to be very difficult, but it does have to increase the heart rate. Also, just like the motion for babies, exercise for older people should not be too simple. Learning some new skills or actions, such as with yoga or tai-chi helps to open up memory paths in the brain that may not have been used for a long time. For most people, any type of physical activity that increases the heart rate is helpful. The main aim is to increase the brain's flow of blood. And your brain can benefit from as little as two to three hours of exercise a week.

    Have you ever wondered why birds sing? Maybe you thought that they were just happy. After all, you probably sing or whistle when you are happy.

    Some scientists believe that birds do sing some of the time just because they are happy. However, they sing most of the time for a very different reason. Their singing is actually a warning to other birds to stay out of their territory.

    Do you know what a "territory" is? A territory is an area that an animal, usually the male, claims（声称）as its own. Only he and his family are welcome there. No other families of the same species are welcome. Your yard and house are your territory where only your family and friends are welcome. If a stranger should enter your territory and threaten you, you might shout. Probably this would be enough to frighten him away.

    If so, you have actually scared the stranger away without having to fight him. A bird does the same thing. But he expects an outsider almost any time, especially at nesting（筑巢）season. So he is screaming all the time, whether he can see an outsider or not. This screaming is what we call a bird's song, and it is usually enough to keep an outsider away.

    Birds sing loudest in the spring when they are trying to attract a mate and warn others not to enter the territory of theirs.

    You can see that birds have a language of their own. Most of it has to do with attracting mates and setting up territories.