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.