The logic behind the trial is deceptively simple. Ecological studies have repeatedly shown that the risk of food allergy increases the further a child lives from the equator, a gradient that tracks with declining ultraviolet B exposure and lower vitamin D status. The Melbourne team behind VITALITY had previously demonstrated that infants with vitamin D deficiency, defined as levels at or below 50 nanomoles per litre, were significantly more likely to have challenge-proven food allergy at twelve months of age, with an adjusted odds ratio of 3.4. Strikingly, that association was modified by parental country of birth: it was strong in infants of Australian-born parents but absent in those with at least one parent born overseas. Biologically, the hypothesis is plausible, because vitamin D is known to be critical to the healthy development and maintenance of the immune system in early life, and it may also influence airway remodelling relevant to asthma.

What makes Australia the ideal laboratory for this question is an accident of public health policy. Unlike many Northern Hemisphere countries, Australia does not routinely fortify its food supply with vitamin D, and it has no population-level recommendation for routine infant supplementation. That means researchers can randomise babies to supplementation or placebo without the background noise of widespread fortification or supplementation contaminating the comparison. VITALITY exploited this natural experiment, enrolling healthy, term, predominantly breastfed, vitamin D-unsupplemented infants across Greater Melbourne between December 2014 and April 2022.

The trial design was rigorous. Infants were randomised to receive either 400 International Units of vitamin D3 as cholecalciferol, one drop per day, or an identical-looking placebo drop of vegetable oil, starting between six and twelve weeks of age and continuing until twelve months. The primary objective was to determine whether supplementation reduces the prevalence of food allergy at twelve months, assessed not by parental report but by the gold standard: skin prick testing followed, where indicated, by supervised oral food challenges. Secondary outcomes included food sensitisation, vitamin D deficiency, doctor-diagnosed eczema, infection episodes, wheeze episodes and allergy-related healthcare use during the first year. The trial was originally powered to detect a 32.5 percent reduction in food allergy from an assumed prevalence of ten percent, but midway through, with updated data showing a 12.4 percent allergy prevalence among breastfed infants, the sample size was recalculated to detect a 30 percent reduction from twelve to eight percent, requiring 2,330 infants.

Recruitment was a feat of persistence. Of 13,537 infants approached through immunisation and maternal-child health clinics across every local government area of Greater Melbourne, 5,679 were eligible, and 2,739 families proceeded to randomisation, a 48.2 percent recruitment rate among those eligible. Then came COVID-19. Melbourne endured 262 days of lockdown across six periods between March 2020 and October 2021, forcing face-to-face recruitment to a halt. The team pivoted to online methods, launching targeted carousel advertisements on Facebook and Instagram aimed at families with newborns. The strategy worked remarkably well: interested families, already familiar with the eligibility criteria from the ads, contacted the study team, and recruitment rates returned to near pre-pandemic levels despite ongoing restrictions.

Retention proved equally impressive. Despite the pandemic, more than 83 percent of participants completed either the twelve-month questionnaire or a short allergy questionnaire, and 78.8 percent attended the twelve-month clinic assessment at the Royal Children’s Hospital. Only 6.4 percent of participants were lost to follow-up and 6.7 percent withdrew before their twelve-month assessment, with the most common reasons being that life was too busy or that giving the daily drops was too difficult. The families who joined were not a random slice of the population: 89.2 percent had a family history of allergic disease, and 61.2 percent had both parents born in Australia. Compared with the population-based HealthNuts and EarlyNuts studies from the same city, VITALITY participants showed a clear allergic bias, most likely because a prevention trial attracts families with lived experience of allergy. This is a limitation the investigators acknowledge openly, but it also means the cohort is enriched for the very outcomes it was designed to study.

The clinical work at twelve months was substantial. Skin prick tests were performed on 2,151 infants, testing sensitivity to cow’s milk, egg, peanut, cashew, almond, hazelnut, shellfish, wheat, sesame, soy and house dust mite. Five hundred infants, 23.3 percent of those tested, had a positive result to at least one food allergen, and 351 of them underwent a total of 612 oral food challenges, the definitive test of true clinical allergy. Of those challenges, 300 were positive, 303 negative and nine inconclusive. Every challenge was conducted under supervision, generating an objective diagnosis rather than the surrogate markers that plague much of the allergy literature.

What truly sets VITALITY apart, however, is the depth of its biological repository. Blood was collected at baseline, at twelve months and at the six-year follow-up, with peripheral blood mononuclear cells separated and frozen in liquid nitrogen for cytokine profiling, flow cytometry and RNA sequencing, and plasma stored at minus 80 degrees Celsius for biomarker analysis. Vitamin D levels were quantified using liquid chromatography-tandem mass spectrometry. At the baseline home visit, researchers collected infant stool, skin swabs from the antecubital fossa and cheek, maternal skin and nasal swabs, and breastmilk. Skin swabs and stool are being used for microbiome analysis, while stool and breastmilk undergo metabolomic profiling. These samples have already yielded results: the skin swabs contributed to a comprehensive genome catalogue of the early-life human skin microbiome, and are now being evaluated for their role in eczema development. Questionnaires at baseline and at six, nine and twelve months captured demographics, environmental exposures, feeding behaviours and factors influencing vitamin D status, all managed through a REDCap electronic data platform.

The story is not over. A six-year follow-up began in 2023, motivated by findings from the HealthNuts study showing that infants with food allergy at one year go on to have lung function deficits and asthma at age six. The follow-up will assess whether early-life vitamin D supplementation can modulate the developing lung, and will track the persistence and emergence of new allergic diseases, lung function, infections and oral health, including dental plaque collection. The timepoint was deliberately aligned with other Melbourne cohorts to enable cross-cohort analyses using validated measures. The team is also linking records to Medicare and Pharmaceutical Benefits data, the Australian Childhood Immunisation Register, hospital admissions, emergency presentations, anaphylaxis notifications and perinatal records, extending linkage to the child’s seventh birthday. Because the cohort was recruited before and during the pandemic, its data also feed a seven-cohort consortium study that documented how COVID-19 disproportionately affected the most disadvantaged Australian families.

For the scientific community, VITALITY represents the first adequately powered study worldwide to test whether infant vitamin D supplementation can prevent allergic disease, and its randomised design means future analyses can adjust for, or stratify by, the intervention when exploring other exposure-outcome relationships. A pre-registered statistical analysis plan, published before any analyses began, specifies multiple imputation for missing data and confidence-interval-based reporting. Applications to access the data and biospecimens are welcomed through the Melbourne Children’s Lifecourse Initiative, meaning this resource will keep generating discoveries long after the primary trial results are known. Whether or not the daily drop of vitamin D turns out to be the answer to the food allergy epidemic, the infrastructure built to test that question, thousands of deeply phenotyped children, a multi-omics biobank spanning gut, skin, blood and breastmilk, and linked health records through early childhood, will shape allergy and immune health research for decades.

Subject of Research: A randomised trial and longitudinal cohort testing postnatal vitamin D supplementation for prevention of food allergy and atopic disease in infants

Article Title: VITALITY – a longitudinal cohort established to assess the role of postnatal vitamin D supplementation in atopic disease and immune health

Article References: VITALITY – a longitudinal cohort established to assess the role of postnatal vitamin D supplementation in atopic disease and immune health. (n.d.). https://doi.org/10.1007/s10654-026-01437-8

Image Credits: AI Generated

DOI: 10.1007/s10654-026-01437-8

Keywords: vitamin D, food allergy, VITALITY trial, infant health, atopic disease, eczema, randomised controlled trial, longitudinal cohort, microbiome, immune health, asthma, pediatric allergy