People with a BMI of 30 or more have a much higher risk of asthma than those with a lower BMI. Seven percent of adults with a BMI in the normal range have asthma, but 11 percent of adults with a BMI classified as obese have asthma. There is growing evidence that obesity increases the risk of developing asthma and severe asthma attacks. In something of a medical trap, asthma also appears to increase the risk of obesity.
Asthma is a disease characterised by inflammation of the airways. Scientific studies have shown that inflammatory substances produced by fat affect the airways and asthma symptoms. Research has shown that genes related to chronic inflammation may be more active in people who are also obese. Scientists also know that obese mothers are more likely to have children with asthma.
According to one study, obesity and maternal weight gain are associated with a 15-30% increased risk of asthma in their children. People who are overweight or obese are more likely to suffer from asthma or wheeze, but scientists did not know exactly why. However, due to differences in Asian populations, there is no clear cut-off point for defining overweight and obesity. Researchers are currently investigating the mechanisms that would explain exactly how asthma might cause obesity or how obesity might cause asthma.
For example, eosinophilic airway inflammation is altered in obesity, with altered trafficking of eosinophils into the airway lumen; sputum eosinophils and exhaled nitric oxide may underestimate the degree of type 2 inflammation in obesity. Genetics has also allowed researchers to dissect the many potential factors that may confound the association between obesity and asthma, such as socioeconomic status, lifestyle factors and environmental exposures. As a result, clinicians who have long suspected that asthma and obesity are linked now have plenty of data to back them up. People with obesity and asthma are also more likely to be depressed, use more medication and experience severe symptoms.
Taken together, the underlying biology of asthma and obesity, as well as personal perception and perhaps bias, may help explain why obese patients do not experience the same level of asthma control as leaner patients. Obesity is significantly associated with the development of asthma, worsening asthma symptoms and poor asthma control. Weight loss should be recommended for all people with severe asthma who are obese, as it can provide a wide range of health benefits. Australian guidelines for the management of obesity recommend measuring both waist circumference and BMI in adults.