A study led by the universities of Fribourg and Zurich and funded by the Swiss National Science Foundation shows that the link between sleep  behaviour and intestinal flora is already present in infancy.

The gut flora of infants is connected to their sleep patterns. This effect is evident from the age of three months, as sleep researchers Salome Kurth of the University of Fribourg and Sarah Schoch of the University of Zurich have now shown. For example, infants with lower diversity of gut bacteria sleep more during the day, and night-time sleep patterns are linked to the type of bacteria in the gut. «Such links were previously known only in adults,» says Schoch. The results of this study, funded by the Swiss National Science Foundation (SNSF), have been published in Progress in Neurobiology.

The researchers also found that sleep, gut bacteria and brain activity co-evolve dynamically during the first year of infancy. In other words, infants with a different profile of bacteria in the gut also have different brain activity during sleep. Strongest links are found at age 3 months, pinpointing a sensitive period.

Infants observed in their environment
The results were obtained from a large longitudinal cohort study of 162 infants in Switzerland. «Many people were involved in this ‹field-study›, for example our team visited families, because we wanted to track the children’s sleep in their natural surroundings – at home, in the pram, in the car – and over longer time periods. That is one of the advantages of our mobile approach, because sleep studies are often limited to a single night of observation in the sleep laboratory,» says Salome Kurth.

Infants were observed in their homes at three different points in time: 3 months, 6 months and 12 months. At each time point in time, a motion sensor was placed on the infant’s ankle to monitor its sleep for ten days. At the same time, parents were asked to keep a diary noting their child’s sleep during this period, as well as bedtimes, night awakenings but also eating and crying behaviour.

Parents were also asked to take stool samples to allow scientists to identify and characterise the infants’ gut bacterial genomics in the laboratory according to three criteria: diversity, maturity (microbiota evolve over the course of a lifetime and particularly in infancy) and the bacterial enterotype (simplified profiles of gut bacteria). As an additional step, parents completed questionnaires to assess a child’s behavioural development status in five domains: communication, gross motor skills, fine motor skills, problem solving and personal social development.

The research team visited about 30 children for a night sleep recording with an electroencephalo- gram at 6 months old.

Promising targets for intervention
«These results are particularly interesting because they show that sleep and gut flora are linked to behavioural development in infants. Importantly, it is possible to improve sleep by specific coaching for parents and to modify the gut flora through changes in diet. These are promising avenues of intervention in cases where behavioural development is a problem,» says Kurth. However, it is too early to generalise the results: the insights from this study need to be transferred to clinical groups in order to find effective application.

> S. Schoch, J.L. Castro-Mej?a, L. Krych, B. Leng, W. Kot, M. Kohler, R. Huber, G. Rogler, L. Biedermann, J.C. Walser, D. Nielsen, S.Kurth: From Alpha Diversity to Zzz: Interactions among sleep, the brain, and gut- microbiota in the first year of life. Progress in Neurobiology (2021).

> This project was supported by the SNSF Eccellenza instrument. Eccellenza Professorial Fellowships are aimed at young researchers who hold an assistant professorship or equivalent position and aspire to a permanent professorship. Leading a large-scale project and a research team at a Swiss university will help them achieve their goal.

> Download image for editorial use. Legend: the gut plays a role in infant sleep. Copyright: provided.

> The project on the SNSF Data Portal