Timing of Exposure to Cow’s Milk Formula and Risk of Developing Cow’s Milk Allergy and Sensitization in the HealthNuts Study

BACKGROUND: The role of exposure to cow's milk formula (CMF) in the first days of life, particularly transient exposure, in the development of cow's milk allergy is unclear. OBJECTIVE: To determine whether the timing of exposure to CMF influences the risk of cow's milk sensitization and allergy at ages 1 and 6 years. METHODS: Participants were 940 children recruited into the population-based, longitudinal HealthNuts study conducted in Melbourne, Australia with linked data available on formula use in hospital. Cow's milk formula use was parent-reported via retrospective questionnaire and supplemented with linked data from the Victorian Perinatal Data Collection. We categorized exposure to CMF in the first 3 months of life as no exposure, very early transient (exposure only in the first week of life), very early persistent (exposure both during and after the first week), and early exposure (after the first week). RESULTS: Overall, 46.9% of infants (n = 398 of 849) consumed CMF in the first 3 months of life; 20.2% of infants started in the first week and continued use, 12.7% had transient use only in the first week of life, and the remaining 14.0% started after the first week of life. At age 1 year, the prevalence of cow's milk sensitization and allergy was 2.1% (17 of 822) and 0.7% (6 of 818), respectively, reducing to 0.5% (4 of 744) and 0.1% (1 of 745 at age 6 years. We found no evidence of an association between very early transient use of CMF and any allergy outcomes at ages 1 or 6 years; however, CIs were wide. In infants who had very early transient exposure to CMF compared with no exposure, the adjusted odds ratio for cow's milk allergy and cow's milk sensitization at 1 year was 1.27 (95% CI, 0.16-10.00; P = .82) and 2.23 (95% CI, 0.76-6.54; P = .14), respectively. CONCLUSIONS: Very early transient use of CMF was not associated with the risk of cow's milk allergy.