Asthma and IgE-reactivity in childhood : risk factors and consequences

Sammanfattning: Many children have asthma-like wheezing symptoms during their first years of life, yet only a minority develop asthma. Attempts to identify wheezing children at increased risk of asthma have been conducted, but the value for the clinician has been limited. The risk of developing asthma is influenced already in utero if the foetus is exposed to maternal tobacco smoke, but prior studies have not been able to differentiate pre- and postnatal smoke exposure effects. Conversely, the role of foetal or early postnatal smoke exposure for the risk of allergic sensitization in childhood is still under debate. It has been suggested that allergies may play a role in the pathogenesis of recurrent abdominal pain due to a mutual immunologic origin. Previous studies investigating potential associations between allergy-like symptoms, IgE-reactivity and abdominal pain have shown contradictory results. The aim of the epidemiological studies in this thesis were to contribute to the knowledge on the role of pre- and early postnatal tobacco smoke exposure for the development of asthma and aeroallergen sensitization in children. We also explored which clinical risk factors and comorbidities to wheezing in infancy that were associated with having asthma at school age. Moreover, associations between allergy-related symptoms and IgE-reactivity during childhood and recurrent abdominal pain at age 12 years were investigated. The results regarding risks of tobacco smoke exposure were based on data from eight European birth cohorts consisting of a total of 32,774 children. The studies on wheeze and school age asthma as well as allergy-related symptoms and abdominal pain were based on data from the population-based Swedish birth cohort BAMSE consisting of 4,089 children. In study I we showed that among the children that wheezed at least once during their first two years of life, the risk of school age asthma was almost fourfold. Allergic heredity, increased severity of wheeze, infant eczema and recurrent abdominal pain were independent risk factors for having asthma at age eight years. In study II, maternal tobacco smoking during pregnancy was associated with an increased risk of wheeze or asthma in preschool children even among the children that had not been exposed late in pregnancy or after birth. We observed no convincing associations between early second hand tobacco smoke exposure and sensitization to pets, house dust mite, pollen or all aeroallergens combined in preschool or school age in study III. In study IV all allergy-related diseases at the age of 12 years were associated with recurrent abdominal pain at the same age. Moreover, food sensitization and food allergy at age four or eight years were also associated with recurrent abdominal pain at age 12 years. The results of this thesis consolidate previous knowledge regarding early factors associated with childhood asthma development. The significant association between allergy-related diseases and recurrent abdominal pain supports the hypothesis of a mutual immunologic pathway. The knowledge that maternal smoking during pregnancy is associated with wheeze and asthma in preschool children, even if they were not exposed late in pregnancy or after birth, should be used to motivate women not to start smoking or to quit before conceiving to prevent asthma in their children.