A systematic review of early life factors which adversely affect subsequent lung function.

It has been known for many years that multiple early life factors can adversely affect lung function and future respiratory health. This is the first systematic review to attempt to analyse all these factors simultaneously. We adhered to strict a priori criteria for inclusion and exclusion of studies. The initial search yielded 29,351 citations of which 208 articles were reviewed in full and 25 were included in the review. This included 6 birth cohorts and 19 longitudinal population studies. The 25 studies reported the effect of 74 childhood factors (on their own or in combinations with other factors) on subsequent lung function reported as percent predicted forced expiration in one second (FEV1). The childhood factors that were associated with a significant reduction in future FEV1 could be grouped as: early infection, bronchial hyper-reactivity (BHR) / airway lability, a diagnosis of asthma, wheeze, family history of atopy or asthma, respiratory symptoms and prematurity / low birth weight. A complete mathematical model will only be possible if the raw data from all previous studies is made available. This highlights the need for increased cooperation between researchers and the need for international consensus about the outcome measures for future longitudinal studies.