ving in densely populated areas.

Effects of the child's physical activity level have also not been studied. However, one recent study found that teens that spend less time in sports activities have more colds and flu, writes Cieslak. Canadian Fifth Graders Tell the Tale In this study, Cie

Time spent in sports keeps kids from getting sick -- and it melts body fat, all of which improves children's health, a new study shows. It's another reason to get children away from computers and TV, and send them outside for exercise. Habitual physical activity of more than three hours a day gives children the best defense against infections such as colds and flu, writes researcher Thomas J. Cieslak, with Brock University in Ontario, Canada. His study appears in the current Journal of Applied Physiology. Exercise has positive impact on the immune system, the body's defense against infection, writes Cieslak.

Studies show that moderate exercise and physical activity enhance immunity and reduce the rates of upper respiratory infections such as colds. . Moreover, stress and obesity suppress the immune system -- although studies have mostly looked at this in adults, he explains. "It has long been suspected that the younger the individual, the less effective the immune defense," writes Cieslak. However, a child's immunity is still developing until the ages of 9 to 11, he says. Also, studies of children's health and immunity haven't taken into account diet, climate, and living in densely populated areas.

Effects of the child's physical activity level have also not been studied. However, one recent study found that teens that spend less time in sports activities have more colds and flu, writes Cieslak. Canadian Fifth Graders Tell the Tale In this study, Cies

ives children the best defense against infections such as colds and flu, writes researcher Thomas J. Cieslak, with Brock University in Ontario, Canada. His study appears in the current Journal of Applied Physiology. Exercise has positive impact on the immune system, the body's defense against infection, writes Cieslak.

Studies show that moderate exercise and physical activity enhance immunity and reduce the rates of upper respiratory infections such as colds. . Moreover, stress and obesity suppress the immune system -- although studies have mostly looked at this in adults, he explains. "It has long been suspected that the younger the individual, the less effective the immune defense," writes Cieslak. However, a child's immunity is still developing until the ages of 9 to 11, he says. Also, studies of children's health and immunity haven't taken into account diet, climate, and living in densely populated areas.

Effects of the child's physical activity level have also not been studied. However, one recent study found that teens that spend less time in sports activities have more colds and flu, writes Cieslak. Canadian Fifth Graders Tell the Tale In this study, Cie

ction, writes Cieslak.

Studies show that moderate exercise and physical activity enhance immunity and reduce the rates of upper respiratory infections such as colds. . Moreover, stress and obesity suppress the immune system -- although studies have mostly looked at this in adults, he explains. "It has long been suspected that the younger the individual, the less effective the immune defense," writes Cieslak. However, a child's immunity is still developing until the ages of 9 to 11, he says. Also, studies of children's health and immunity haven't taken into account diet, climate, and living in densely populated areas.

Effects of the child's physical activity level have also not been studied. However, one recent study found that teens that spend less time in sports activities have more colds and flu, writes Cieslak. Canadian Fifth Graders Tell the Tale In this study, Cie

"It has long been suspected that the younger the individual, the less effective the immune defense," writes Cieslak. However, a child's immunity is still developing until the ages of 9 to 11, he says. Also, studies of children's health and immunity haven't taken into account diet, climate, and living in densely populated areas.

Effects of the child's physical activity level have also not been studied. However, one recent study found that teens that spend less time in sports activities have more colds and flu, writes Cieslak. Canadian Fifth Graders Tell the Tale In this study, Cie

ving in densely populated areas.

Effects of the child's physical activity level have also not been studied. However, one recent study found that teens that spend less time in sports activities have more colds and flu, writes Cieslak. Canadian Fifth Graders Tell the Tale In this study, Cieslak looked at immunity, physical fitness levels, stress levels, and body fat in a group of fifth graders -- all 10 and 11 years old -- while they were in school from May through June. This is a moderate to high infection season in Canada. Researchers found that 22% of boys reported getting less than three hours physical activity daily, compared with 32% of girls.

Also, children's health was affected:

· Children getting less than three hours a day had significantly lowered immune system, more body fat, and reported more sick days than more fit and active children.

· 40% of these less-active children had more than 25% body fat; they also reported more colds and flu than other kids.

The results mirror findings in studies of teens and adults -- that less activity increases susceptibility to infections. "The results of the present study suggest that this may also be true in children," writes Cieslak.

Child's Immune System Complex

However, because a child's immune system is more complex, other factors such as time of day or year -- or whether they're in school or not -- could also affect their immune systems, he says. Winter or colder temperatures m