Exposure to air pollutants PM
(B), tobacco smoke and wheezing. Values are overall odds ratios (95% confidence interval) from generalized estimating equation models based on average air pollution levels from birth until the age of 3 years with wheezing at the ages of 1, 2 and 3 years combined, representing the risks of wheezing per 10 μg/m3 increase in PM10 or NO2 stratified for tobacco smoke exposure * p <0.05. Models are adjusted for maternal age, education, parity, history of atopy or asthma and children’s ethnicity, sex, gestational age, birth weight, breastfeeding, daycare attendance, pet keeping and lower respiratory tract infections at 1, 2 and 3 years of age. P-values for interaction: tobacco smoke exposure * average level PM10, p-value <0.05; tobacco smoke exposure * average level NO2, p-value <0.01.