Cohort profile: the vitamin A and D and nitric oxide (AD-ON) observational cohort on lung development and symptoms in premature and mature children in North Zealand, Denmark

PURPOSE: The risk of developing asthma-like symptoms and asthma in childhood is influenced by genetics, environmental exposures, prenatal and early postnatal events, and their interactions. The cohort name refers to vitamins A and D, and nitric oxide (NO) spelt backwards and this cohort profile paper aims to present the data collection and aim of the cohort. The overall aim when establishing this cohort was to investigate if childhood lung function can be traced back to early neonatal lung function and fractional exhaled NO (FeNO) and investigate prenatal and postnatal risk factors including maternal and neonatal vitamin A and D levels in preterm and term born children. PARTICIPANTS: One thousand five hundred women and their babies born at Nordsjaellands Hospital in Denmark from 2013 to 2014 were included in the AD-ON research biobank prior to birth. Neonates from the AD-ON research biobank, admitted to the Neonatal Intensive Care Unit at Nordsjaellands Hospital, were included in the AD-ON neonatal cohort. The neonatal cohort consisted of 149 neonates hereof 63 preterm and 86 term born. The children in the cohort have been invited to follow-up visits at age 1 and 6 years. FINDINGS TO DATE: Published data from this cohort includes a validated and clinically applicable method to measure FeNO in neonates. We found an age-specific pattern of association between respiratory symptoms at age 1 and neonatal FeNO in preterm children. Moreover, we found that the respiratory symptoms risk was associated with postnatal factors (Respiratory Syncytial Virus infection and parental smoking) in preterm infants and prenatal factors (parental asthma and maternal infection during pregnancy) in term born infants. FUTURE PLANS: In the future, the children will be examined continuously with 3-year to 5-year intervals until the age of 18. Lung function, allergy tests, environmental exposure measurements and questionnaires will be collected at each follow-up visit.