The gut microbiota and sleep in infants: a focus on diurnal rhythmicity patterns

Emerging evidence supports a bidirectional relationship between the gut microbiome and sleep, which is partly mediated by the microbiota‒gut‒brain axis. Infancy is a critical window for the establishment of both the gut microbiome and sleep regulation, which we hypothesize to be linked across both short (diurnal) and long (monthly) time scales. In this longitudinal study, we investigated associations between gut microbiota development and sleep patterns in 20 infants at 2, 4, and 6 months of age (n = 163 samples). Infants were continuously monitored across 48-h sampling periods. The gut microbiota profiles were characterized using 16S rRNA gene sequencing; gut melatonin concentrations were measured; sleep data were collected via wearable actimetry, 24-h parent-reported sleep diaries, and the Brief Infant Sleep Questionnaire; and parenting style and behavioral development were assessed. In some infants, bacterial diversity followed diurnal rhythmic patterns. While bacterial rhythmicity was not significantly associated with sleep rhythmicity, infants with higher microbial alpha diversity showed more robust sleep patterns. Infant age emerged as the strongest predictor of gut microbial diversity and melatonin levels. Our findings suggest that gut microbial establishment may support the maturation of sleep‒wake rhythms in early infancy. Further research is needed to elucidate mechanistic roles of the gut microbiome in sleep development.