OBJECTIVETo evaluate the interaction effects of breastfeeding and passive smoking on asthma and asthma related symptoms among children.

METHODSUsing a cluster random sampling method, 2 elementary schools and 1 kindergarten were randomly selected from 7 cities of Liaoning province. The resulting 25 elementary schools and 50 kindergartens were included, and 31 049 children from the selected schools living up to 2 years were recruited in this survey. The information about the children's type of feeding up, living environment, passive smoking exposure, respiratory diseases and symptoms were collected. The interaction effects of breastfeeding and passive smoking on asthma and asthma related symptoms (persistent cough,persistent phlegm, current wheeze and allergic rhinitis) were evaluated with Glimmix procedure.

RESULTSThere were 31 049 children involved in this investigation. The age was (8.32 ± 2.75) years old. There were 23 987 (77.26%) children with breastfeeding and 11 820 (38.07%) children with passive smoking. The prevalence of asthma and allergic rhinitis were 6.22%(1491/23 987), 4.67%(1120/23 987) in children with breastfeeding, and were 7.70%(544/7062), 5.48%(387/7062) in children without breastfeeding,compared to the children without breastfeeding, the children with breastfeeding had lower risk of asthma(OR = 0.79, 95%CI:0.72-0.88) and allergic rhinitis(OR = 0.85, 95%CI:0.75-0.95); The prevalence of current wheeze was 7.89%(929/11 770) in children with father smoking, and was 5.37%(1036/19 279) in children without father smoking, compared to the children without father smoking, the children with father smoking increased the risk of current wheeze(OR = 1.51, 95%CI:1.38-1.65). The prevalence of persistent cough was 18.96%(51/269) in children with mother smoking, and was 9.51%(2926/30 780) in children without mother smoking,compared to the children without mother smoking, the children with mother smoking increased the risk of persistent cough(OR = 2.23, 95%CI:1.64-3.03). The prevalence of persistent phlegm was 5.69%(871/5316) in children with anyone smoking, and was 3.50%(550/15 733) in children without anyone smoking, compared to the children without anyone smoking, the children with anyone smoking increased the risk of persistent phlegm(OR = 1.67, 95%CI:1.49-1.86).Glimmix procedure analysis showed there was a significant interaction effects between breastfeeding and passive smoking. The estimated OR for father smoking among breastfeeding children were consistently lower than those among non-breastfeeding children for asthma. The estimated OR for mother smoking among breastfeeding children were consistently lower than those among non-breastfeeding children for allergic rhinitis. The estimated OR for anyone smoking among breastfeeding children were consistently lower than those among non-breastfeeding children for asthma and allergic rhinitis(all P values < 0.05).

CONCLUSIONBreastfeeding decreases the detrimental effects of passive smoking on asthma and asthma related symptoms in children.