They looked those with adult onset asthma, and those with adult onset asthma who were not overweight at age 18, said a release of California Cancer Centre.

Compared with women of normal weight -- body mass index (BMI) below 25 -- women who were obese were more than twice as likely to have adult onset asthma, and extremely obese women were more than three times more likely to have asthma.

The researchers also found that large waist circumference (more than 88 cm) was associated with increased asthma prevalence even among women with a normal BMI.

Women who were obese and overweight were at greater risk of severe asthma attacks, shown by urgent medical visits and hospital admissions.

The study was published in Thorax.