Language processing in breastfed infants at risk of thiamine deficiency benefits from maternal thiamine supplementation.

In a double-blind, randomized controlled trial, we investigated relationships between infants' exposure to thiamine and their language-processing ability. Three hundred thirty-five lactating Cambodian mothers of 161 female/174 male infants received either 0, 1.2, 2.4, or 10 mg of thiamine daily, from 2 to 24 weeks postpartum. We assessed infants' language processing at 24 weeks via the infant-directed speech (IDS) task, measuring attentional enhancement to IDS versus adult-directed speech. Maternal thiamine supplementation displayed a small but statistically significant dose-response relationship to the magnitude of infants' IDS-elicited attentional enhancement (adjusted R² = 0.022, p = .011). As well, only infants whose mothers received a daily thiamine supplement of 10 mg showed fully robust IDS-related attentional enhancement. These findings showcase the IDS Task for monitoring the integrity of infants' language processing and underscore the importance of adequate thiamine early in life for ensuring optimal language development. (PsycInfo Database Record (c) 2025 APA, all rights reserved).