Allergy

Association of carbon monoxide levels with allergic diseases in children

Kim J, Han Y, Seo SC, Lee JY, Choi J, Kim KH, Woo SY, Kim EH, Kwon HJ, Cheong HK, Oh I, Ahn K. Allergy Asthma Proc 2016; 37(1): 1–7

Air pollution and allergic disease

Exposure to air pollutants has been proposed to contribute to the development or aggravation of allergic disease, particularly in children. 1A recent report in Allergy and Asthma Proceedings has investigated childhood exposure to air pollution and its impact on the incidence of atopic dermatitis (AD), allergic rhinitis (AR) and asthma. 1

Children are vulnerable to air pollution

Children are particularly vulnerable to airborne pollutants:

• Their lungs are not fully developed until 6–8 years of age and damage occurring during childhood may result in remodelling of the airways 2
  
• Children may be exposed to higher levels of air pollutants than adults as they generally spend more time outdoors, have higher baseline rates of ventilation, and are less likely to breathe nasally than adults 2
  
• Their immune system is immature 2

Study design

Children of 6–7 years of age were recruited from 45 Korean schools by random selection using a two-stage cluster sampling design. 1The prevalence of AD, AR and asthma was assessed by parental questionnaire and by physical examination for the presence of eczema in the neck and arms. 1

Exposure to air pollution during each participant’s first year of life, and in the year proceeding the study was estimated by analysis of publically available data from 235 air quality monitoring sites. Only participants who were born, or who lived within 2 km of an air quality monitoring site were included in the analysis. 1

The pollutants investigated included sulphur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO) and particulate matter of aerodynamic diameter of ≤10 µm (PM10). 1

Logistic regression analysis was used to control for factors of sex, education of parents, allergic diseases of parents, passive smoking and family income. 1

Lifetime allergic rhinitis risk was associated with exposure to carbon monoxide during infancy. 1

CO exposure increases risk of allergic disease in children

Exposure to ambient CO during the first year of life was associated with an increased lifetime prevalence of AR. For a 100 parts per billion (ppb) increase in mean daily CO levels, the adjusted odds ratio (aOR) was 1.10 (95% confidence interval [CI] 1.03–1.19, n=1828). Differences in exposure to SO2, NO2, O3 and PM10 between children with and without AR were not found. None of the air pollutants investigated affected the prevalence of asthma or AD following exposure during the first year of life. 1

CO levels close to the family home were correlated with current AD symptoms. The aOR for presence of AD symptoms at the time of survey was 8.11 (95% CI 1.06–62.12, n=1894) for each 1 ppm increase in mean annual CO level in the past year. These findings are consistent with previous reports linking air pollutants, including CO, with aggravation of eczema. However, the mechanisms by which pollution affects skin inflammation or irritation are poorly understood. 1

In contrast, exposure to O3 was correlated with reduced risk of current AD; a 1 ppb increase in the daily maximum 8 hours average O3 resulted in an aOR of 0.72 (95% CI 0.57–0.91). The authors hypothesised that this correlation may be due to an inverse spatiotemporal association between O3 and NO2 in polluted urban areas. 1

While the nature of the link between air pollutants and allergic disease is not yet clear, the generation of reactive oxygen species has been proposed as a potential mechanism. 1

Study limitations and conclusions

The authors emphasised that although SO2, NO2, O3 and PM10 were not significantly correlated with increases in the risk of allergic disease in this study, it should not be concluded that these pollutants are not harmful for children. One limitation of this study was that air quality measurements were not taken at the participant’s home, but at the nearest monitoring site. 1

This study demonstrated that CO exposure during infancy is a risk factor for AR and that exposure to higher CO levels in the past year increases the risk of AD symptoms. 1

Report on: Association of carbon monoxide levels with allergic diseases in children. Kim J, Han Y, Seo SC, Lee JY, Choi J, Kim KH, Woo SY, Kim EH, Kwon HJ, Cheong HK, Oh I, Ahn K. Allergy Asthma Proc 2016; 37(1): 1–7.

Reference list

1. Kim J, Han Y, Seo SC, Lee JY, Choi J, Kim KH, et al. Association of carbon monoxide levels with allergic diseases in children. Allergy Asthma Proc 2016; 37(1): 1–7.
   
2. Bateson TF, Schwartz J. Children’s response to air pollutants. J Toxicol Environ Health A 2008; 71(3): 238–243.