“…Paternal age at birth was analyzed either as a continuous variable or as a categorical variable with four groups, including < 30 (reference group), 30–34, 35–39, and ≥ 40 years. The adjusted covariates were listed as follows: child’s age, sex, height, maternal age at birth, prematurity (gestational age less than 37 weeks), birth weight, cesarean delivery, birth order, physician-diagnosed asthma, parental university education, parental allergic diseases (physician-diagnosed asthma, allergic rhinitis or atopic dermatitis in mother, father or both), prenatal exposure to ETS (one or more household smokers during gestation), breastfeeding (exclusive or partial) longer than 6 months, and household income, which were similar to previous relevant studies [ 12 , 14 , 17 , 23 ]. We performed subgroup analysis, stratified by prenatal exposure to ETS and breastfeeding which were associated with lung function and FeNO in previous studies [ 24 – 29 ], to evaluate potential effect modifiers.…”