Short-term exposure to relative humidity and lung health in early adolescents

Extremes in humidity can induce bronchoconstriction and trigger breathing symptoms in people with asthma. Less is known about how humidity influences measurements of lung health in children and adolescents. Our objective was to assess the extent to which short-term exposures to high and low relative humidity (RH) are associated with lung function and fractional exhaled nitric oxide (FeNO) in adolescents.

We included adolescents (mean age 13.2 y, SD: 0.9) from a northeast US prospective prebirth cohort (n = 1019). We assigned daily RH levels to geocoded participant addresses. We defined low or high RH as ≤10^th or ≥90^th internal percentiles, respectively, of the cohort-specific RH distribution and the reference RH as the median. We evaluated the linearity of associations of RH in the 1-7 days before assessment with forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC), and FeNO using generalized additive models with penalized splines (df = 3). We log-transformed FeNO due to non-normality. For nonlinear relationships, we used distributed lag nonlinear models to explore the cumulative effects of lag 1-7 day RH on FEV₁, FVC, and FeNO.

Median RH was 65.6% (interquartile range [IQR] = 19.8%), 10th percentile 47.2%, 90th percentile 86.6%. Mean FeNO (SD) was 25.9ppb (26.9ppb). High (vs. median) RH was associated with 38.0% higher FeNO (95% CI = 10.3, 72.7). Exposure to low (vs. median) RH was associated with 186.2 ml lower FEV₁ (95% CI = -299.2, -73.3) and -130.2 ml lower FVC (95% CI = -251.9, -8.5).

Short-term exposures to extremes of RH were associated with lower lung function and higher FeNO, a measure of airway inflammation, in adolescents.