Obesity-asthma link needs research
19 May 2005

The relationship between obesity and asthma needs to be investigated in greater depth urgently, according to a new report by US researchers.

More than 50% of American adults are obese, and 75% of people needing emergency treatment for asthma in the US are overweight, says the review from a team led by Dr Jeffrey Fredburg of the Harvard School of Public Health.

In Britain one in ten six-year-olds is now obese, and the UK has among the highest levels of childhood asthma in the world.

Given the increase in both conditions in developed countries, Dr Fredburg believes that the link between the two needs more research. 'Obesity has the capacity to impact lung function in a variety of ways,' he explained. 'None of them are good and all of them are poorly understood.'

Existing studies make a strong case for a link between obesity and asthma: research shows that while many children seem to shake off their symptoms during adolescence, of those who do not, a disproportionate amount are overweight. Studies also point to the increased likelihood of adults with larger waistlines developing asthma compared to their leaner counterparts.

Dr Fredburg suggests that even though people who lose weight may go on to experience reduced symptoms, in some cases obesity can cause the airways to change irreversibly, so they are hyper-sensitive and prone to narrowing.

Reporting in the Journal of Allergy and Clinical Immunology Dr Fredburg considers a number of reasons why obese people are more likely to have asthma: in obese people the lungs are often not fully expanded, and breathing is shallower, which makes it more likely that airways are narrower; obese people are also more susceptible to long-term low-level inflammation of the airways as a result of their fat tissue.

'The importance of understanding [the relationship between asthma and obesity] is underscored by the extremely high prevalence of obesity in inner-city children, who are at the greatest risk of asthma; and by observations indicating that obesity is a strong predictor of the persistence of childhood asthma into adolescence,' he concludes.