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 (FEV 1 ). The childhood factors that were associated with a significant reduction in future FEV 1 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.

SummaryChronic obstructive pulmonary disease (COPD) is the third most common cause of mortality worldwide and it is important to discover whether risk factors can be identified from studies undertaken in childhood.Numerous longitudinal cohort studies have been developed in many parts of the world to better understand the long-term outcomes of chronic respiratory diseases. Using data they have generated, it should be possible to identify specific risk factors in children and develop a model to prioritise their importance when found, in order to consider ways to reduce the prevalence and/or severity of disease in adults. However, this does require the sharing of data within the field, as is happening in other related fields, such as the Virtual International Stroke Trial Archive (www.vista.gla.ac.uk). Pooling of the raw data could be very informative and an organisation such as the European Respiratory Society could play an important role in ensuring this happens.Unfortunately, cohort studies vary widely in their inclusion criteria, their methodology and the format in which lung function data are presented. The raw data required to develop a model to assess the impact of childhood risk factors on future lung function have not been made available from many of the published articles.Our initial belief that recognised risk factors are independent variables was naïve and a different approach is required to better understand their interdependence.