Using questionnaire data, researchers looked at the relationship between BMI and the severity of asthma symptoms in 1,113 asthma patients aged 35 years or older, from two cities in the north-western US. Nearly 40 per cent of the patients were obese.
Each patient gave demographic data and information about smoking status, corticosteroid use in the past month, and any evidence of gastro-oesophageal reflux disease (GORD).
Overall, 60 per cent reported using inhaled corticosteroids in the previous month, 21 per cent reported poor asthma-related quality of life, and 29 per cent poor asthma control.
In addition, 6 per cent reported hospitalisation for asthma within the past year.
When other factors were taken into account, patients with a BMI score greater than 30 were found to have more severe asthma exacerbations than people who had a BMI of less than 25.
Patients in this group were 2.8 times more likely to report poor quality of life relating specifically to the condition, 2.7 times more likely to report poor asthma control and 4.6 times more likely to have a history of asthma-related hospitalisation.
The researchers concluded that obese patients with asthma required more intensive monitoring and treatment to improve outcomes.
They also suggested that weight-loss programmes targeted at patients with asthma should be developed.
The study group's lead researcher, Dr David Mosen, of the Kaiser Permanente Center for Health Research in Portland, Oregon, said: 'Even adjusting for risk factors, obese adults were nearly five times more likely to be hospitalised for their asthma.
'This study is yet another example of the dangers of obesity, along with heart disease, diabetes, stroke and dementia,' he said.
J Allergy Clin Immunol 2008; 122: 507-11.
Comment below and tell us what you think