Growth pattern during early infancy, body mass index during childhood and childhood asthma

Background There is a lack of longitudinal studies of associations between growth from infancy to childhood and asthma development. Objective The objective of the study was to investigate the effects of weight change during infancy, body mass index (BMI) and the interaction of these factors on the risk of childhood asthma. Methods We enrolled children born in 2008 and 2009 at full‐term and with normal birth weight. The weight change in infancy was grouped into slow, on‐track and rapid. BMI status in childhood was stratified into low, normal and high groups and used as a time‐varying variable. The outcome was asthma, defined as two or more diagnoses of asthma separated by at least 1 year after 2 years of age. The risk of asthma was assessed using Cox proportional hazard regression, with adjustment for sex, residence area at birth, economic status and feeding types in infancy. Results Of 917,707 children born in Korea in 2008 and 2009, 271,871 were eligible for analysis. The risk of asthma was greater in groups with low birth weight (aHR 1.06, 95% CI 1.04 to 1.08), rapid body weight change during early infancy (aHR 1.08, 95% CI 1.07 to 1.10) and high BMI during childhood (aHR 1.06, 95% CI 1.04–1.08). The interaction of weight change during early infancy with BMI during childhood was significant for asthma (p