Children who are overweight, or were heavy at birth, are significantly more likely than their peers to develop asthma, a new research review shows.

In an analysis of a dozen previous studies on weight and asthma risk, researchers found that overweight school-age children were 50 percent more likely than their normal-weight peers to develop asthma.

In addition, high birthweight was linked to a 20 percent greater risk of developing asthma later in childhood, according to findings published in the journal Archives of Disease in Childhood.

The rate of asthma among U.S. children has shot up over the past 20 years. It’s possible that a “significant portion” of this rise can be explained by the simultaneous upswing in childhood obesity, according to lead study author Dr. Valerie Flaherman of the University of California San Francisco.

The current findings, she told Reuters Health, offer one more reason to prevent excessive weight gain in childhood.

Obesity could contribute to asthma development in a number of ways, Flaherman and co-author Dr. George Rutherford note in their report.

For example, dietary effects could be at work; some research suggests that antioxidant vitamins and “good” fats in foods like fish can lower the risk of asthma, and heavy children may be getting lower amounts of these nutrients.

Other potential factors include the pressure that excess pounds places on the airways or the higher prevalence of acid reflux among overweight children.

Body weight is only one factor in asthma development. The authors note it likely plays a small role when compared with factors such as family history of asthma, genetic predisposition to allergies, and air pollution.

Still, Flaherman said, the evidence from this review suggests that preventing childhood obesity would also prevent some cases of asthma.

SOURCE: Archives of Disease in Childhood, April 2006.