PM_2.5, Black Carbon, and NO₂ Associations With Rhinitis and Asthma Multimorbidity in Adults: The Constances Cohort

Rhinitis and asthma often co-occur; however, studies on their associations with air pollution have always considered them separately.

We investigated the association between long-term air pollution exposure and rhinitis and asthma multimorbidity in adults.

We used data at inclusion from Constances, a large French population-based adult cohort. Current rhinitis (CR) and current asthma (CA) were defined by questionnaire. Annual exposure to nitrogen dioxide (NO₂), particulate matter 2.5 μm or less (PM_2.5), and black carbon were estimated by linking participants' residential address to land-use regression models. We performed cross-sectional multinomial logistic regressions between each air pollutant and CR alone, CA alone, and CR+CA (no-CR/no-CA being the reference) adjusted for age, sex, smoking, education level, and French deprivation index.

Among the 177,968 participants included in the analyses (mean age 47 years; 54% female), 111,108 were classified as no-CR/no-CA (62%), 49,971 CR alone (28%), 6,435 CA alone (4%), and 10,454 CR+CA (6%). One interquartile range (IQR) increase of black carbon and NO₂ was significantly associated with the three phenotypes, with adjusted odds ratios from 1.04 to 1.13 for BC (IQR = 0.55-10^-5·m^-1), and from 1.06 to 1.14 for NO₂ (IQR = 13.7 μg·m^-3). For PM_2.5, one IQR increase (4.09 μg·m^-3) was significantly associated with CR alone and CR+CA. In all our analysis, the highest associations were observed for CR alone.

Our results show that long-term air pollution is more associated with rhinitis alone or with asthma multimorbidity than with asthma alone.