Joint effects of birth outcomes and childhood body mass index on respiratory symptoms.

Thinness in infancy and higher childhood body mass index (BMI) are risk factors for poor respiratory health. However, few studies have examined the joint effects of birth outcomes and childhood BMI on the occurrence of respiratory symptoms. A total of 78,011 Taiwanese middle-school children were investigated between 1995 and 1996 in a nationwide International Study of Asthma and Allergies in Childhood (ISAAC) survey, with standardised height/weight measurement. Their survey data was compared successfully with the birth registration dataset. Childhood BMI was positively associated with all respiratory symptoms, with greater effects and significant risks associated with serious phenotypes in the video questionnaire. Children with a history of low birth weight (LBW), those who were born prematurely (pre-term), or those who were small for gestational age (SGA) were also more likely to have allergic respiratory symptoms. As birthweight and gestational age were not positively associated with childhood BMI, we proposed that LBW, pre-term birth and childhood BMI were independent factors for respiratory symptoms. LBW, pre-term birth and childhood BMI are all independent risk factors for respiratory symptoms in children. Children with a history of LBW, pre-term birth or SGA and a higher current BMI might have larger respiratory burden.