Washington, Sep 5 (IANS): It is more probable that childhood obesity contributes to asthma rather than the other way round, says a study.

For years, doctors have known that there is a link between childhood obesity and asthma, but have found it difficult to determine which condition tends to come first, or whether one causes the other.

"The relationship between obesity and asthma in adults, which shows that being overweight and obese can precede the onset of asthma, is supported by a number of studies," said lead author of the study Perdita Permaul from Massachusetts General Hospital in the US.

"There is not as much evidence for children, but the progression from obesity to asthma, rather than the other way around, seems probable," Permaul added.

Citing a study that showed that rapid growth in body mass index (BMI) during the first two years of life increased the risk of asthma up to six years of age, the team shows that the onset and duration of obesity and the composition of the excess fat can affect lung function.

"Most kids who suffer from asthma also have allergies," said Michael Foggs, president, American College of Allergy, Asthma and Immunology (ACAAI).

"These allergic responses in the lung can lead to symptoms of allergy,” Foggs added.

The study appeared in the journal Annals of Allergy, Asthma and Immunology.