Can the effects of outdoor air pollution on asthma be mitigated?

Abstract

Outdoor air pollution affects lung development, asthma morbidity, and early life exposure to outdoor pollutants has been linked with development of asthma. Recent findings suggest that several non-modifiable and modifiable factors may diminish or augment the harmful effects of outdoor air pollution on asthma. While genetic studies have been limited by sample size and or issues with replication, interactions have been demonstrated between the GSTM1-null genotype and ozone, along with NO2 and adenylate cyclase 2. Co-exposure to psychosocial stress and air pollutants is associated with asthma and reduced lung function in children, particularly among males. Cigarette smoking is associated with incident asthma among adults with outdoor pollutant exposure, but studies examining a potential interaction between second-hand smoke and outdoor pollutants are lacking. Concurrent exposure to aeroallergens and air pollutants is associated with increased airway inflammation in adults and asthma in atopic children. Some studies support an interaction between obesity and air pollution on lung function in adults and respiratory symptoms in children. Nutritional factors, including antioxidants, may attenuate the detrimental effects of air pollution by reducing airway inflammation. Vitamin E was associated with decreased airway inflammation in adults with asthma, while reductions in lung function in children exposed to ozone were attenuated with supplementation of vitamins C and E. Vitamin D supplementation reduced the effects of TRAP and allergen exposure in a murine model examining airway inflammation and vitamin D deficiency or insufficiency is associated with increased asthma morbidity in children. Diets rich in fruit and vegetables and the Mediterranean diet are associated with greater lung function among children exposed to ozone. Conclusions: Policy measures related to improved air quality have been effective at improving respiratory symptoms and objective measures such as lung function. The findings of our review suggest that public health policies related to modifiable risk factors such as smoking, second-hand smoke exposure or obesity may both significantly reduce the harmful effects of air pollution and greatly benefit overall health. Further, certain populations that remain exposed to air pollution may benefit from identification of key interventions that mitigate the harmful effects of pollutants via well-designed clinical trials.