THURSDAY, Sept. 27 (HealthDay News) -- Formal physical exercise programs for children have only a small impact on overall activity and thus on weight loss, British researchers report.

Their study raises questions about the best ways to help children attain or maintain a healthy weight.

"Physical activity interventions are not increasing physical activity sufficiently to impact on the body mass or body fat of children," said lead researcher Brad Metcalf, of the department of endocrinology and metabolism at Peninsula College of Medicine and Dentistry in Plymouth, England. "It is in everyone's interest to find something that works effectively," he added.

But other experts said instead of dismissing organized interventions as ineffective, policymakers should conclude that still more is needed to stem childhood obesity. In the United States, about 17 percent of children aged 2 years and older are obese.

"I disagree that the importance of physical activity to childhood obesity control, or health promotion, has been called into question by this study," said Dr. David Katz, director of the Yale University Prevention Research Center in New Haven, Conn.

On the contrary, "we have cause to question if we are doing enough to make routine activity the cultural norm, so that such programming can achieve greater effects," Katz said. "An intervention, no matter how good, can only achieve so much if not surrounded by cultural supports."

Katz also faulted the study for not including data from the many studies that show a significant benefit from exercise.

For the study, published in the Sept. 27 online edition of the BMJ, the researchers analyzed 30 studies conducted between 1990 and 2012 involving children aged 16 and under.

This type of study, known as a meta-analysis, is used to find common threads running through multiple studies. Problems with this type of analysis can arise from the weakness of any of the studies included and the difficulty of combining disparate data.

Unlike some other studies of children's activity, these studies measured actual movement during children's waking hours using accelerometers and didn't rely on questionnaires.

Eight of the 30 studies included only overweight or obese children. One U.S. study followed more than 700 children, average age 11, taking part in 90 minutes of after-school physical activity three times a week. Another involved more than 250 Scottish nursery school children who did 30 minutes of physical activity three times a week.

Overall, the researchers said the programs achieved "small-to-negligible" increases in children's total activity with small improvements in time spent in moderate or vigorous intensities -- about four minutes' walking or running per day.

This could have only a minimal effect on weight, they concluded.

"It's been shown by others that four minutes extra walking/running is only associated with a 2 millimeter difference in waist circumference," Metcalf said. While the added activity sessions might offer other benefits, including better coordination, improved ability at a sport, team participation and genuine enjoyment, they won't "have a meaningful impact on obesity prevention," he said.

These programs may not work because they might replace physically demanding after-school activities that take place outdoors and last for longer periods, the researchers said. It's also possible that children eat more after these sessions, they noted.

Mark Hamer, from the department of epidemiology and public health at University College London and co-author of an accompanying journal editorial, said the study has limitations but "provides the best evidence to date on the effectiveness of physical activity interventions in childhood."

Better approaches to increasing children's physical activity are needed, Hamer said. Perhaps physical changes to the indoor and outdoor environment can facilitate activity, he suggested.

He and others maintain that a wealth of evidence supports the association between an active lifestyle and better health.

Samantha Heller, exercise physiologist and clinical nutrition coordinator at the Center for Cancer Care at Griffin Hospital in Derby, Conn., pointed out that programs that aim to boost children's activity levels may not influence sedentary behavior at home or once the programs conclude.

Also, "many interventions do not include a nutrition component that could impact food choices, overall nutrition or calorie intake," she said.

School environments need to shift toward a more active day for kids, Heller said. "We need to continue to develop programs, environments and classes that encourage and educate children and teens on the importance of exercise and physical activity in ways that are meaningful and fun for them," she added.

More information

For more information on childhood obesity, visit the U.S. Centers for Disease Control and Prevention.

FRIDAY, Sept. 28 (HealthDay News) -- A common herbicide called atrazine may be associated with a rare birth defect of the nasal cavity, a new study suggests.

Atrazine -- the most widely used herbicide in the United States, particularly in corn crops -- is believed to be an endocrine disruptor, which means that it may interfere with the hormone system in humans.

The new study looked at the link between atrazine and choanal atresia, a birth defect in which tissue formed during fetal development blocks the back of the nasal passage. The condition affects a baby's ability to breathe. Surgery is the typical treatment.

Although few risk factors for choanal atresia have been identified, it's believed that chemicals that disrupt a mother's hormone system may be associated with the risk, according to study author Philip Lupo, an assistant professor of pediatrics -- hematology/oncology at Baylor College of Medicine and Texas Children's Cancer Center.

He and his colleagues found that mothers who lived in Texas counties with the highest levels of atrazine use were 80 percent more likely to have children with choanal atresia -- or a less severe form of the condition called choanal stenosis -- than those in counties with the lowest levels of atrazine use.

"Our results warrant more detailed exploration before any public health or policy-related recommendations are made, but this study is a good first step in trying to understand the origin of this birth defect, including a possible role of atrazine," Lupo said in a Baylor news release.

The study appears Sept. 28 in the Journal of Pediatrics.

While the study found an association between the herbicide atrazine and the birth defect choanal atresia, it did not prove cause-and-effect.

More information

The Children's Choanal Atresia Foundation has more about choanal atresia  .

THURSDAY, Sept. 27 (HealthDay News) -- Long before Hollywood introduced the concept of "Mean Girls," people knew that childhood can be full of name-calling, manipulation and we-won't-talk-to-you freeze-outs. Now, a new study finds that "social bullying" isn't just a real-life phenomenon. It's also common in the TV shows popular among kids aged 2 to 11.

From "American Idol" to "The Simpsons," the study authors found, the people and characters who appear on these shows are often mean. They insult one another, connive to get what they want and bully others in non-physical ways.

The researchers said 92 percent of 150 episodes reviewed featured some form of "social aggression" -- on average about 14 incidents per hour.

"Lots of attention has been paid to exposure to nudity and violence in the media, and rightfully so," said study lead author Nicole Martins, an assistant professor in the department of telecommunications at Indiana University. "But parents are largely unaware that programs could be teaching children to be cruel and mean to each other as well. Just because a show is low on physical violence doesn't mean it's harmless."

The researchers examined 150 episodes of the 50 most popular shows among kids aged 2 to 11 in 2005. They included a variety of shows for kids (such as "Hannah Montana," "Suite Life of Zack & Cody," "SpongeBob SquarePants") and a few adult shows ("American Idol," "Survivor," "The Simple Life 3").

"Social aggression is pretty prevalent," Martins said. Females tend to perpetrate it, she noted, and they are often attractive.

The researchers had a wide definition of social bullying. For example, they counted the insult wars between the judges of "American Idol" and a scene on "The Simpsons" when Mr. Burns told Homer Simpson he was a "waste of skin and fat."

"We laugh at it," Martins said, "but in real life it's harmful. Also, we don't see any punishments or negative consequences for these behaviors. People call each other mean names and say mean things about each other, and nothing happens. The victim takes it or fires back."

There was physical bullying, too. The researchers reported that they saw it in about 80 percent of the shows examined.

Martins acknowledged that TV shows wouldn't be very interesting to watch if everybody behaved properly and treated each other with respect.

"I'm not saying get rid of the conflict. No one wants to watch that," she said. "I'd challenge people in the industry to think about how they portray these aggressive behaviors and at least show that the victim is hurt by the comments." That, she added, can reduce the risk that children will imitate what they see on TV.

The research, however, doesn't prove that the behavior of children is influenced by the way people and characters act on the TV shows.

Robert Faris, an assistant professor at the University of California, Davis, who studies bullying, praised the study but said it's unlikely that "any amount of hand-wringing on the part of health advocates will change programming."

Still, he said, "perhaps if viewers were able to see the underlying meanness of some forms of humor, they might not find it so funny. It is certainly possible to be hilarious without being mean, and I do sense that audiences might be starting to tire of 'snark' and sarcasm."

What to do? Faris said his research has shown that among teens, "aggression of all forms is rooted in the competition for social status, and this competition takes place within dense friendship networks."

He suggested that parents encourage kids to form "true" friendships that are more stable and less vulnerable: "Hopefully they come out of high school with four lifelong friends, not 400 Facebook friends."

The study appeared online recently in the Journal of Communication.

More information

For more about bullying, try the U.S. National Library of Medicine.

WEDNESDAY, Sept. 26 (HealthDay News) -- Infants in urban areas have different patterns of viral respiratory illness than those in the suburbs, which may explain why inner-city children are more likely to develop asthma, a new study suggests.

The findings may lead to new ways to treat childhood asthma, according to Dr. James Gern of the University of Wisconsin, Madison, and colleagues.

Previous studies have linked viral respiratory illnesses to the development of asthma in children and have shown that children with human rhinovirus infections are more likely to develop asthma by age 6 than those with respiratory syncytial virus infections.

In this study, researchers analyzed nasal secretions from 500 infants living in inner-city areas of Boston, Baltimore, New York City and St. Louis, and 285 infants from suburban Madison, Wis. The samples were taken while the children were healthy, and also when they had respiratory illnesses.

Inner-city infants had lower rates of human rhinovirus and respiratory syncytial virus than suburban infants, but were more likely to test positive for adenovirus infections -- 4.8 percent of urban babies tested positive for adenovirus only versus 0.7 percent of suburban babies.

Adenovirus can cause persistent infections and the researchers suggested that adenovirus infections early in life could alter the development of the lungs or airways. The investigators plan to follow the inner-city kids for at least 10 years to determine whether adenovirus infections are associated with increased rates of asthma and lower levels of lung function.

The study was published online Sept. 26 in the Journal of Infectious Diseases.

More information

The American Lung Association has more about children and asthma  .