The effects of birthweight and breastfeeding on asthma among children aged 1-5 years.

Aim: Asthma is a major cause of morbidity and mortality among children and has steadily increased in prevalence. The combined effect of birthweight and breastfeeding on childhood asthma remains unclear.
Methods: In this study, we analysed a nationally representative sample of children aged 1-5 years from the National Health and Nutrition Examination Survey 1999-2002. Logistic regression was performed to examine the hypothesis whether birthweight and breastfeeding are independently associated with the prevalence of asthma after accounting for the complex sampling design. In addition, we sought to describe the relationship between birthweight and childhood asthma and to assess the potentially combined effect between birthweight and breastfeeding on asthma among children aged 1-5 years after considering the possible effects of social and environmental factors.
Results: We found that birthweight (measured continuously) was inversely and linearly associated with the prevalence of childhood asthma (odds ratio (OR) = 0.80 per 1 kg increase in birthweight, 95% confidence interval (CI): 0.65-0.98). Using a categorical variable, low birthweight (LBW) was positively associated with childhood asthma (OR = 1.28, 95% CI: 0.81-2.68). Furthermore, we detected an interaction between birthweight and breastfeeding on childhood asthma. Breastfeeding had a strong protective effect on asthma among children with high birthweight (OR = 0.14, 95% CI: 0.04-0.43) while it had no significant effect on asthma among children with normal birthweight or LBW.
Conclusions: The mechanisms underlying these relationships remain uncertain and warrant further explanation.