Early life factors and the long-term development of asthma

Abstract: Asthma, a huge burden on millions of individuals worldwide, is one of the most important public health issues in many countries. As genetic and   environmental factors interact, asthma may be programmed very early in life, perhaps even in utero.The aim of this thesis was to assess the impact of gestational age, cord blood immunoglobulin E (IgE), a family history of asthma, migration, and pertussis immunization in early life on the development of asthma in child and adult populations.As a proxy for asthma disease, dispensed asthma medication was used as the main outcome variable based on data from the Swedish Prescribed Drug  Register. Data from other national registers were used to control for  confounders. Three of our studies were based on national cohorts, and one on a local birth cohort that was initiated in 1974–75.Gestational age had an inverse dose-response relationship with dispensed asthma medication in 6– to 19-year-olds. Odds ratios for dispensed asthma medication increased with degree of prematurity compared with children born in term. Furthermore, asthma medication was more likely to be dispensed among children and adolescents born early term after 37–38 weeks’ gestation than among those at the same age who were born in term.Elevated cord blood IgE and a family history of asthma in infancy were associated with a two- to threefold increased likelihood of dispensed asthma medication and self-reported allergen-induced respiratory symptoms at the age of 32–34 years, but the predictive power was poor.Age at migration had an inverse dose-response relationship with dispensed asthma medication at the age of 6–25 years in adoptees and foreign-born children with foreign-born parents. International adoptees and children born in Sweden to foreign-born parents had three- to fourfold higher rates of asthma medication compared with foreign-born children who were raised by their foreign-born birth parents.No association was found between pertussis immunization in early infancy and dispensed asthma medication in 15-year-olds. The type of vaccine or vaccine schedule did not affect the outcome.Fetal life is a vulnerable period. This thesis strengthens the evidence that every week of gestation is important for lung maturation. Cord blood IgE, however, did not predict the risk of asthma in adults. Furthermore, the study of migrating populations demonstrated that environmental changes at any age during childhood may affect the risk of asthma. Another, important public health message from this thesis is that vaccination against pertussis in early childhood can be considered safe with respect to the long-term development of asthma.