Timing-specific longitudinal links between the infant gut microbiome and negative affect in toddlerhood

The role of the early life gut microbiome in children’s risk for psychopathology has gained increasing interest in recent years. Most research on this topic has focused on the first three to four years of life because this is a critical period for developing connections between the gut microbiome and the brain. Prior research has identified associations between variability in the composition and diversity of the gut microbiome in infancy and markers of temperamental risk for psychopathology, including negative affect. However, the specific microbes affected, and the directionality of these associations have differed between studies, likely due to differences in the developmental period of focus and assessment approaches. In the current preregistered study, we examined connections between the gut microbiome, assessed at two time points in infancy (2 weeks and 18 months of age), and negative affect measured at 30 months of age in a longitudinal study of infants and their caregivers. We found that infants with higher gut microbiome diversity and Veillonella abundance at 2 weeks of age, and higher Ruthenibacterium abundance at 18 months, showed more observed negative affect during a study visit at 30 months. These results suggest timing-specific associations between the gut microbiome and negative affect even within this early critical period.