Table 1 Definition of early life events, environmental and lifestyle factors, and allergic diseases at age 15
Definition | Assessment | |
|---|---|---|
Early life events | ||
Parental atopy | positive if the mother or father had asthma, eczema or hay fever | asked at birth; questionnaire-based |
Parental education | three categories based on the highest number of education years of either parent (high: >10 years; medium: 10 years; low: <10 years) | asked at birth; questionnaire-based |
Maternal age at delivery | dichotomized in ≤31 years and >31 years (mean age served as cut-off) | asked at birth; questionnaire-based |
Maternal smoking during pregnancy | yes vs no | asked at birth; questionnaire-based |
Early second-hand smoke exposure at home | positive if parents reported at least once that the child was exposed to second-hand smoke at home | asked up to age 4 (at 4 months, 1 year (control arm only) and yearly at 2 to 4 years in GINIplus; half-yearly from birth to 2 years and at age 4 years for past 24 months in LISAplus); questionnaire-based |
Season of birth | dichotomized (December to February (winter) versus other seasons) | Birth month derived from date of birth; questionnaire-based |
Birth weight | continuous, grams | asked at birth in LISAplus and at 1 year in GINIplus; questionnaire-based |
Breastfeeding | exclusive breastfeeding for at least four months | asked separately for 1–6 months at 1 year in GINIplus and at 6 months in LISAplus; questionnaire-based |
Peak weight and peak height velocity | maximum of the first derivative of the individual weight or height gain curves obtained between birth and two years of age (calculated using nonlinear random effects models) [9] | weight and height measurements obtained during the children’s preventive medical check-ups to monitor growth |
Early lower respiratory tract infections | doctor’s diagnosis of pneumonia or obstructive bronchitis within the first three years of life (hereon referred to as lung infections) | asked up to age 3 (yearly in GINIplus; half-yearly up to age 2 years and up to age 3 years asked at the 4 year follow-up in LISAplus); questionnaire-based |
Environmental and lifestyle factors at age 15 | ||
Short-term air pollution exposure | continuous, the average of the daily concentrations of NO2, PM2.5 mass and PM10 mass (μg/m3) | obtained for the seven days prior to lung function testing from monitoring sites near the centers of Munich and Wesel [8] |
Long-term air pollution exposure | continuous, long-term concentrations of NO2, PM2.5 mass and PM10 mass (μg/m3) | estimated to each participant’s home address at birth, 10- and 15-years, respectively [8] |
Regular indoor second-hand smoke exposure | positive if the adolescent reported indoor second-hand smoke exposure at least once a week | asked at age 15 years; one question in GINIplus, two questions for second-hand exposure: (1) at home and (2) in other locations in LISAplus (positive if regular exposure was reported in at least one question); questionnaire-based |
Active smoking | yes vs no | asked at age 15 years, questionnaire-based |
Vitamin D concentrations | continuous; serum 25-hydroxyvitamin D [25(OH)D] concentrations adjusted for seasonal variance using a generalized additive model (nmol/l) [36] | measured at age 15 years using Roche’s vitamin D total test (E170, Roche Diagnostics, Mannheim, Germany) |
Body mass index | continuous, kilogram per square meter (kg/m2) | calculated using body height and weight obtained at lung function testing |
Current allergic diseases | ||
Asthma | defined based on the Global Allergy and Asthma European Network (GA2LEN) definition [44]. Subjects were considered as currently having asthma if they responded positively to at least two of the three following questions: (1) Has a doctor diagnosed asthma in your child at the age 3 to 15 years? (2) Has your child taken asthma medication during the last 12 months? (3) Has your child had wheezing or whistling in the chest in the last 12 months? | parents were asked to provide yearly information on their child’s doctor diagnosed allergic diseases throughout childhood; information on current allergic symptoms and asthma medication in the last 12 months was derived from the last follow-up questionnaire at age 15 years. |
Current allergic rhinitis | positive if one of the following questions was positive: (1) Has a doctor diagnosed hay fever (i.e. seasonal allergic rhinitis) in your child? (2) Has a doctor diagnosed perennial allergic rhinitis in your child? | asked separately for ages 11 to 15, at the 15-year follow-up;questionnaire-based |
Sensitization to food or aeroallergens | food allergen mixture including egg white, codfish, cow milk, wheat flour, peanut, and soybean and aeroallergen mixture including cat, dog, mugwort, birch, timothy, rye, Cladosporium herbarum, and Dermatophagoides pteronyssinus; for both tests, a value >0.35 kU/L was considered positive | measured by serum specific Immunoglobulin E (IgE) using the ImmunoCAP Specific IgE system (Phadia GmbH, Freiburg, Germany) at age 15 years |