Breastfeeding duration modified the effects of neonatal and familial risk factors on childhood asthma and allergy: a population-based study

BACKGROUND: Childhood asthma and allergic diseases are a significant global problem. There are inconsistent findings on the associations of delivery mode, the number of children in the household and breastfeeding with childhood asthma and allergic diseases. We assessed these associations and examined whether breastfeeding modified the effects of neonatal and familial risk factors on childhood asthma and allergic diseases. METHODS: A population-based cross-sectional study was conducted in Shanghai, China. A total of 17 primary schools were randomly selected from 13 districts of Shanghai in this study. The International Study of Asthma and Allergies in Childhood questionnaire was adopted to assess the childhood asthma and allergic diseases. Multivariable logistic regression models were used to evaluate the associations between neonatal and familial factors and childhood asthma and allergic diseases, and to examine the modification effects of breastfeeding on the associations assessed. RESULTS: Of 10,464 primary school children aged 6–11 years, the overall prevalence of childhood asthma, allergic rhinitis, urticaria, food allergy and drug allergy was 13.9, 22.7, 15.3, 8.1 and 4.6%, respectively. Male sex, high socioeconomic status, cesarean section delivery, only one child in the household and having family history of allergy were associated with increased odds ratio (OR) of childhood asthma and allergic diseases while longer breastfeeding duration (> 6 months) was inversely associated with these diseases. Longer breastfeeding duration also attenuated the OR of neonatal and familial risk factors on childhood asthma and allergic diseases. For instance, the adjusted OR of childhood asthma in the group of vaginal delivery and breastfeeding duration > 6 months was lowest (0.78, 95% confidence interval: 0.66, 0.92). CONCLUSIONS: Longer breastfeeding duration was inversely associated with childhood asthma and allergic diseases, and also reduced the OR of neonatal and familial risk factors on these diseases. Giving the prevalence of childhood asthma and allergic diseases is rapidly rising across the globe, these findings may have important clinical and public health implications.