Nitrogen Dioxide, Paediatric Asthma and Adolescent Psychotic Experiences

A paper just published in the new journal Lancet Planetary Health underlines the role of air pollution for paediatric asthma. But did you know that air pollution might also be associated with psychotic experiences in adolescence?

Pattanum Achakulwisut from George Washington University in Washington, DC, and colleagues modelled childhood asthma incidence attributable to nitrogen dioxide (NO2) from global datasets for both exposure and outcome and combined them with estimates of risk derived from the scientific literature (Achakulwisut et al., Lancet Planetary Health 2019, online April 10th, 2019; open access). The authors come to the conclusion that 4 million new cases of paediatric asthma worldwide per year could be attributable to NO2 pollution, that is 13% of the incidence (= new cases). Regional differences are large, with the highest burden in Andean Latin America. While Lima, Peru’s capital, is the city with the highest number of new paediatric asthma cases attributable to NO2 air pollution (more than 600 new cases per year per 100,000 children), the most consistent and striking finding is the high percentage of paediatric asthma incidence in China: 48% of all new asthma cases in Shanghai are attributable to NO2 pollution, with similarly high numbers in many other large Chinese cities. However, especially the large cities in North America are on a comparable level. Los Angeles, New York City and Toronto have more than 500 new cases of childhood asthma per year per 100,000 children. For Cologne in Germany the authors calculated a number of approximately 250 cases.

While the association of airway diseases with air pollution seems to be quite reasonable, Joanne Newbury from King’s College, London, recently reported a more striking association of air pollution with adolescent psychotic experiences (Newbury et al., JAMA Psychiatry, online March 27th, 2019; open access). These authors asked more than 2000 participants of the Environmental-Risk Longitudinal Twin Study (a population-based cohort study of 2232 children born in 1994 and 1995 in England and Wales) at age 18 whether they had had psychotic experiences in their adolescence (age 12 – 18). 30% of the sample reported at least one psychotic experience. Psychotic experiences were significantly more common among adolescents with the highest level of annual exposure to NO2, NOX and particulate matter, with an increase in risk of up to 70%.

The higher incidence of psychosis in urban compared to rural environments has been well established. The authors of this study now state: “Together NO2 and NOX statistically explained 60% of the association between urbanicity and adolescent psychotic experiences.“ They speculate that nitrogen oxides may cause inflammatory processes with direct influences on brain function. Furthermore, because NO2 and NOX are linked to vehicle emissions, the association could also be driven by noise pollution, which has been linked to stress, sleep disturbance, and cognitive impairment in children and adolescents. The authors conclude “Therefore, the association of NO2 and NOx with adolescent psychotic experiences may have been linked more generally to road traffic and noise pollution experienced by participants living near busy roads.”

Whatever the direct causal relationships are: The effects of environmental pollution on the health of our children are obvious, and they call to action.

Rajen Naidoo from the University of KwaZulu-Natal, South Africa, in an accompanying editorial to the Lancet Planetary Health paper concludes (Naidoo, Lancet Planetary Health 2019, online April 10th, 2019; open access): „An important outcome from this study is the further evidence that the existing WHO standards are not protective against childhood asthma. Achakulwisut and colleagues estimated that approximately 92% of the childhood asthma incidence attributable to NO2 exposure was in areas with NO2 concentrations below the values of the WHO annual average guidelines. This strengthens the case for the downward revision of these global standards and for stronger national policy initiatives in countries without air quality standards. Furthermore, these findings not only support the association of NO2 exposure with childhood asthma incidence, but also, because this pollutant serves as an important proxy for broader traffic related air pollutants, highlight that urgent intervention is necessary to protect the health of those most vulnerable in society: children, particularly those with pre-existing respiratory disease.”