Timing of food introduction and food‐related allergic symptoms in childhood: Evidence from the Japan environment and Children's study ( JECS )

BACKGROUND: The optimal timing for introducing complementary foods remains under debate. Although guidelines generally recommend introducing solids around 4-6 months of age, evidence linking timing to later food allergy remains inconsistent. We evaluated associations between age at food introduction, caregiver-reported food-related allergic symptoms, and allergen-specific immunoglobulin E (IgE) levels up to 6 years of age. METHODS: Using data from the Japan Environment and Children's Study (JECS; 2011-2014), a nationwide birth cohort, we analyzed caregiver-reported food-related allergic symptoms in 63,693 children and allergen-specific IgE levels in a subcohort of 2964 children. Logistic regression assessed associations between timing of food introduction and reported symptoms, and multiple regression evaluated associations with IgE titers. RESULTS: Introduction of certain foods at ≥13 months was associated with higher odds of caregiver-reported food-related allergic symptoms, particularly for egg and wheat (egg: aOR 5.69; wheat: aOR 26.69). Some associations were also observed for soy, fish and rice, although estimates were unstable in small subgroups. Children not introduced to egg or milk by 12-13 months had higher egg white- and cow's milk-specific IgE levels at 2, 4, and 6 years. No significant associations were observed for fruit, shellfish, buckwheat, or peanuts. CONCLUSIONS: Delayed introduction of selected foods beyond 12-13 months was associated with higher odds of caregiver-reported food-related allergic symptoms and, for measured allergens, elevated IgE levels. Given the observational design and questionnaire-based outcomes, findings should be interpreted cautiously.