2.1 Study population & design
Our analyses were carried out within the framework of the PreDicta study, a 2-year multi-center prospective cohort study that has been conducted across five major European cultural and climatic regions (Greece, Germany, Belgium, Poland and Finland).26
We included 140 pre-school children aged 4-6 years with a diagnosis of mild to moderate asthma confirmed by a doctor (in the preceding 2 years, according to the GINA guidelines 2005) as cases, which were previously recruited for the PreDicta study. Eligibility criteria for the PreDicta study included the ability to perform a peak expiratory flow (PEF) measurement at least once and a minimum of 3 wheezing episodes within the last 12 months prior to study inclusion (one of them within the last six months). Exclusion criteria were severe asthma, more than six courses of oral steroids during the last 12 months prior to study inclusion, immunotherapy, chronic medication use or the history of chronic respiratory disease other than asthma and/or allergic rhinitis (e.g. cystic fibrosis). Additional exclusion criteria were an asthma exacerbation and/or upper respiratory tract infection within 4 weeks prior to study inclusion. The cross-sectional control group consisted of 53 healthy, age-matched children with no history of asthma/wheezing or any other allergic disease.
At recruitment, a detailed questionnaire on demographic characteristics, as well as asthma activity and control was handed out. Asthma was classified as uncontrolled, partly controlled or controlled according to the GINA guidelines12. As part of the questionnaires, weekly vigorous PA and daily television attendance (TVA) were assessed. PA with an intensity higher than 4 metabolic equivalents (METs) was classified as vigorous and included brisk walking, bicycling, gymnastics, dancing, basketball, soccer, athletics, tennis, swimming, jumping rope and general participation in active outdoors games. Such activity had to be continuous and cause sweating and heavy breathing for periods longer than 15 minutes.
Whole blood was obtained at baseline for the analysis of cytokine responses of peripheral blood mononuclear cells (PBMCs) cultured in the presence of various stimuli.
Written informed consent was obtained from parents/guardians of all the children recruited in the PreDicta study. The study protocol was approved by the local Ethics Committee of all participating institutions.