Long-term nitrogen exposure linked to wider consequences

People exposed to nitrogen (NO₂) in the long term are at risk of a range of diseases, including cardiovascular, respiratory, and musculoskeletal diseases, according to a study conducted in China.

Researchers used data from the China Kadoorie Biobank and looked at 512,724 Chinese adults between 30 and 79 years of age (mean baseline age 52.0 years, 59.0 percent female). Long-term NO₂ exposure was examined in relation to aggregated disease incidence. Then, the incidences of 12 specific diseases (within the cardiovascular, respiratory, and musculoskeletal diseases) that had shown the strongest association with NO₂ in the analyses of aggregated endpoints were evaluated.

Analyses were stratified by age-at-risk (in 1-year scale), study area, and sex, with adjustments for education, household income, smoking status, alcohol intake, cooking fuel type, heating fuel type, self-reported health status, BMI, physical activity level, temperature, and relative humidity.

Over approximately 6.5 million person-years of follow-up, between 5,285 and 144,852 incident events were documented for each of the 14 aggregated endpoints. Risks of chapter-specific endpoints rose with every 10-μg/m³ increase in annual average NO₂ exposure. This was especially true for cardiovascular (n=144,852; hazard ratio [HR], 1.04, 95 percent confidence interval [CI], 1.02–1.05), respiratory (n=73,232; HR, 1.03, 95 percent CI, 1.01–1.05), musculoskeletal (n=54,409; HR, 1.11, 95 percent CI, 1.09–1.14), and mental and behavioural disorders (n=5,361; HR, 1.12, 95 percent CI, 1.05–1.21).

Looking at specific diseases, significant positive supra-linear associations were seen for hypertensive disease (HR, 1.08, 95 percent CI, 1.05–1.11), lower respiratory tract infection (HR, 1.03, 95 percent CI, 1.01–1.06), arthrosis (HR, 1.15, 95 percent CI, 1.09–1.21), intervertebral disc disorders (HR, 1.13, 95 percent CI, 1.09–1.17), and spondylopathies (HR, 1.05, 95 percent CI, 1.01–1.10). Additionally, linear associations were observed for ischaemic heart disease (HR, 1.03, 95 percent CI, 1.00–1.05), ischaemic stroke (HR, 1.08, 95 percent CI, 1.06–1.11), and asthma (HR, 1.15, 95 percent CI, 1.04–1.27).

NO₂ exposure, used as a negative control, showed a strong lack of association with external causes (n=32,907; HR, 0.98, 95 percent CI, 0.95–1.02).

The findings highlight the importance of implementing the recently tightened WHO air quality guidelines.