2.1 Study design and population
Lifelines is a multi-disciplinary prospective population-based cohort study examining in a unique three-generation design the health and health-related behaviours of 167,729 persons living in the North of the Netherlands. It employs a broad range of investigative procedures in assessing the biomedical, socio-demographic, behavioural, physical and psychological factors which contribute to the health and disease of the general population, with a special focus on multi-morbidity and complex genetics. Baseline examinations in individuals aged 6 months to 93 years took place between 2006 and 2013 with follow-ups visits every 5 years and follow-up questionnaires in between.11 The Lifelines cohort study was approved by the Medical Ethics Committee of the University Medical Center Groningen, Groningen, The Netherlands (2007/152). All subjects gave written informed consent.
For the TRACKER study, subjects between 4 and 18 years of age at baseline, who had completed the questionnaire about allergic diseases and a follow-up questionnaire concerning food allergies, were included.