Childhood asthma and household exposures to nitrogen dioxide and fine particles: a triple-crossover randomized
Janneane F Gent1, Theodore R Holford1, Michael B Bracken1
1The Yale Center for Perinatal, Pediatric and Environmental Epidemiology, Yale School of Public Health, New Haven, Connecticut, USA.
Insights
Reducing household nitrogen dioxide (NO2) or fine particles did not significantly decrease asthma symptoms in children. However, air purifiers targeting fine particles showed modest symptom reduction in small urban homes.
Area of Science:
- Environmental Health
- Pediatric Asthma Research
- Air Quality and Health
Background:
- Persistent asthma in children is often exacerbated by indoor air pollutants.
- Household nitrogen dioxide (NO2) and fine particles are common triggers for asthma symptoms.
- Effective interventions to reduce indoor air pollution exposure are needed.
Purpose of the Study:
- To investigate if reducing household nitrogen dioxide (NO2) or fine particle exposure lowers asthma symptoms in children.
- To evaluate the efficacy of air purifiers designed for NO2 reduction versus particle filtration.
Main Methods:
- A triple-crossover randomized controlled trial was conducted with 126 children (5-11 years) with persistent asthma.
- Participants used three types of air cleaners over 5-week periods: NO2 reduction, particle filtration, or control.
- Asthma symptom-days were the primary outcome, assessed using linear mixed models.
Main Results:
- NO2-reducing air cleaners significantly lowered measured NO2 levels but did not reduce asthma symptom-days compared to the control.
- Particle-reducing air cleaners showed a trend towards fewer asthma symptom-days (1.8 fewer out of 14) compared to the control, though not statistically significant.
- Modest reductions in asthma symptoms were observed with particle-reducing air cleaners in small, urban homes.
Conclusions:
- Current air cleaner technology may not achieve sufficient NO2 reduction to impact asthma symptoms.
- Air cleaners targeting fine particles may offer modest benefits for asthma symptom reduction in specific home environments.
- Further research is needed for combined interventions targeting both NO2 and fine particles.
Objective:
Triple-crossover randomized controlled intervention trial to test whether reduced exposure to household NO2 or fine particles results in reduced symptoms among children with persistent asthma.
Methods:
Children (n = 126) aged 5-11 years with persistent asthma living in homes with gas stoves and levels of NO2 15 ppb or greater recruited in Connecticut and Massachusetts (2015-2019) participated in an intervention involving three air cleaners configured for: (1) NO2 reduction: sham particle filtration and real NO2 scrubbing; (2) particle filtration: HEPA filter and sham NO2 scrubbing; (3) control: sham particle filtration and sham NO2 scrubbing. Air cleaners were randomly assigned for 5-week treatment periods using a three-arm crossover design. Outcome was number of asthma symptom-days during final 14 days of treatment. Treatment effects were assessed using repeated measures, linear mixed models.
Results:
Measured NO2 was lower (by 4 ppb, p < .0001) for NO2-reducing compared to control or particle-reducing treatments. NO2-reducing treatment did not reduce asthma morbidity compared to control. In analysis controlling for measured NO2, there were 1.8 (95% CI -0.3 to 3.9, p = .10) fewer symptom days out of 14 in the particle-reducing treatment compared to control.
Conclusions:
It remains unknown if using an air cleaner alone can achieve levels of NO2 reduction large enough to observe reductions in asthma symptoms. We observed that in small, urban homes with gas stoves, modest reductions in asthma symptoms occurred using air cleaners that remove fine particles. An intervention targeting exposures to both NO2 and fine particles is complicated and further research is warranted.
Registration Number:
NCT02258893.
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