VITALITY - a longitudinal cohort established to assess the role of postnatal vitamin D supplementation in atopic disease and immune health.

VITALITY was established as a single-centre, doubleblind, randomised controlled trial (RCT) to determine whether daily supplementation of 400 International Units (IU) of vitamin D in the first year of life reduces the prevalence of food allergy at 12 months of age, compared to placebo. It recruited 2739 healthy, term, breastfed infants from 2014 to 2022 in Greater Melbourne, Australia. With an overall high retention rate despite the COVID-19 pandemic of over 83%, VITALITY is a rich cohort with extensive samples and data at baseline (six-12 weeks) and at six-, nine- and 12-months of age. Questionnaires collected information on demographics and environmental exposure, allergic diseases, infant feeding and factors thought to influence vitamin D levels at all timepoints. The majority of participants had a family history of allergic disease (89.2%) and 61.2% had both parents born in Australia. The standardized clinic visit at 12 months of age, attended by 79% of participants, included skin prick tests (SPT) +/- oral food challenges (OFC) and eczema assessment. Biospecimen collection included blood, skin and nasal swabs, stool and breastmilk which can be used for multi-omics profiling. Overall we performed SPTs on 2151 infants and undertook 612 OFCs. A six year follow up of VITALITY participants is underway and will determine the effect of early-life vitamin D supplementation on outcomes of asthma and other allergic diseases, lung function, infection and oral health. VITALITY is a large longitudinal cohort with data collected at multiple timepoints in childhood on a range of health outcomes. It provides a unique opportunity to explore early-life risk factors including genetic and environmental markers for food allergy, asthma, other atopic and non-communicable diseases as the cohort matures, in addition to establishing the role of vitamin D as an early-life strategy for prevention of disease and sustaining immune health.