Respiratory health effects of nitrogen dioxide exposure and current guidelines

This article reviews (i) the role of nitrogen dioxide (NO2) in respiratory diseases, including asthma, and (ii) appraises whether current guidelines f or NO2 confer an adequate margin of safety for asthmatics. Medline and Exce rpta Medica (1966-1997) were searched to retrieve original epidemiological studies which examined the relationship between NO2 and respiratory disease s including asthma, Previously reported reviews of controlled clinical stud ies were also utilised. The results of this search were then related to cur rent NO2 guidelines. The review of 23 outdoor and 36 indoor studies suggest s that respiratory effects are associated with levels of NO2 that may be en countered in common domestic and outdoor settings. Meta-analyses of studies among the general population of children demonstrate a 20% increase in res piratory problems, including increases of asthma by 20%, and wheezing by 12 % in households with gas cookers. Epidemiological evidence also indicates t hat hourly NO2 values of 80 ppb are likely to cause respiratory symptoms in the general population of children, Such levels are frequently present in domestic and school settings. Critical appraisal of the epidemiological evi dence indicates the need for a revision of NO2 guidelines to protect both a sthmatics and the general population, especially children.