Twenty to thirty five percent of adults worldwide with asthma are cigarette smokers, rates which are surprisingly similar to the general population. People with mild to moderate asthma who smoke cigarettes have worse symptoms, are more likely to attend hospital with an attack of asthma, and often have a different type of airway inflammation than non-smokers with asthma. Little is known about the effects of current or former cigarette smoking on clinical outcomes or inflammation in the 5% to 10% of people who have severe asthma.

In an article recently published in The Journal of Allergy and Clinical Immunology (JACI), Thomson et al. studied the effect of current and former cigarette smoking on asthma control and airway inflammation in people with severe asthma. They compared patient characteristics, clinical outcomes, and biomarkers of inflammation in current smokers (9%), former smokers (28%), and never smokers (62%) within a group of 760 patients with severe asthma recruited to the British Thoracic Society Severe Asthma Registry in the UK.

The researchers found that current smokers with severe asthma had poorer asthma control, more unscheduled health care visits, more rescue courses of oral steroids, and higher anxiety and depression scores than never or former smokers with severe asthma. The inflammatory profile in sputum and blood also differed. Current smokers were more likely to have a non-eosinophilic type of airway inflammation, and thus more likely to be poorly responsive to corticosteroids, whereas the airway inflammatory profile in former smokers was similar to never-smokers with asthma. Both current and former smokers had reduced blood specific allergy antibody levels to several common environmental allergens.

These findings show that current smokers with severe asthma exhibit worse symptoms and health-care outcomes compared to never smokers and former smokers with severe asthma. Their inflammatory profiles in sputum and blood differ, which may influence the effectiveness of some treatments for severe asthma and may also provide clues for improved therapy.