Epidemiology of pollution-induced airway disease in Japan

Air pollution has been implicated as one of the factors responsible for the increased incidence of allergic diseases seen over recent years. Epidemiological studies in Japan demonstrate that atopic subjects living in urban areas are more likely to suffer from the effects of air pollution, with increased coughing, sputum production, wheezing and throat irritation. Furthermore, animal studies show that high concentrations of pollutant gases can promote airway sensitization. The incidence of allergic rhinitis and asthma have been shown to be greater in areas where there is heavy traffic and hence high levels of automobile exhaust emissions. Intranasal administration of diesel exhaust particles in mice produces a stimulatory effect on immunoglobulin E production, and a similar finding has also been shown with suspended particulate matter in air. Air pollutants, such as ozone and nitrogen dioxide (NO2), have been shown to stimulate the production of granulocyte-macrophage colony stimulating factor, which may play a vital role in airway hyperreactivity and asthma. In comparative studies of asthma in urban and rural areas, history of airway infection and a younger age of onset were found to be significantly greater in urban areas. When the asthmatic patients were divided into two groups according to environmental NO2 levels (group I: NO2 > 30 ppb; group II: NO2 < 30 ppb), no significant difference regarding the various parameters was noted between the two groups, except for a greater severity of asthma in adults in group I, and a greater severity in children in group II. These studies imply that air pollution may be one reason for the increase in allergic diseases in Japan, but a definitive conclusion cannot be drawn, and further investigation is warranted.