Hydrolysed proteins in infant formula and child neurodevelopment up to the age of 3·5 years: the nationwide Étude Longitudinale Française depuis l'Enfance (ELFE) birth cohort.

While breast-feeding is the recommended feeding mode in infancy, rates are low in some Western societies, and infants are widely fed formula. France, in particular, shows high rates of infant formula use, including formulas with protein hydrolysates. The degree of protein hydrolysis has previously been associated with neurodevelopmental outcomes. The present study examines the associations between the protein's hydrolysis degree in infant formula and child neurodevelopment up to 3·5 years of age in the French nationwide Étude Longitudinale Française depuis l'Enfance (ELFE study). Parents reported on brand and name of the formula used at 2 months, and protein hydrolysis degree was derived from the ingredient list. Analyses were based on 6979 infants (92·2, 6·8 and 1 % consuming non-hydrolysed, partially and extensively hydrolysed formulas, respectively). Neurodevelopment was assessed at age 1 and 3·5 years with the Child Development Inventory (CDI), at age 2 years with the MacArthur-Bates Communicative Development Inventories and at age 3·5 years with the Picture Similarities sub-scale (British Ability Scales). Associations between protein hydrolysis degree and child neurodevelopment were assessed using linear and logistic regression for overall scores and poor CDI sub-domain scores (<25th centile), respectively. Among formula-fed infants, protein hydrolysis degree in infant formula was not associated with overall neurodevelopmental scores up to 3·5 years. Some associations were found with the motor skills CDI sub-domain, but they were not consistent at 1 and 3·5 years as well as across sensitivity analyses. The use of hydrolysed formula appears safe in terms of overall neurodevelopment, and research should further investigate specific neurodevelopmental domains.