When an infant’s sleep hinges on a few bacteria

A sleep-brain-gut linkage. That is what a recent study has found. We already knew that in adults, sleep and gut microbiota were doubly interrelated: a deterioration in sleep modifies the composition of the gut microbiota and, conversely, the microbial composition of the gut impacts sleep. But we did not previously know the age at which this two-way link became established between sleep and gut microbiota, or what the potential consequences on development might be.

This was what justified this longitudinal study involving 162 healthy infants at 3, 6, 12 and 24 months of age.

There is a connection between sleep and gut microbiota as early as 3 months of age

First confirmation: the composition of the gut microbiota does indeed start to change as of 6 months of age. The majority of the children in the study experienced a change in flora which went from predominantly Bifidobacterium (enterotype A) to a microbiota rich in Bacteroides (enterotype B), with increased alpha diversity (sidenote: α diversity A measurement indicating the diversity of a single sample, i.e. the number of different species present in an individual. Hamady M, Lozupone C, Knight R. Fast UniFrac: facilitating high-throughput phylogenetic analyses of microbial communities including analysis of pyrosequencing and PhyloChip data. ISME J. 2010 Jan;4(1):17-27. ) .

Above all, the study demonstrates a link between sleep habits and gut microbiota from as early as 3 months: 

• Daytime sleep (duration, number of naps and their regularity) has a negative association with bacterial diversity: infants who sleep the most during the day have less bacterial diversity;
• Nighttime sleep fragmentation and variability are linked to bacterial maturity and enterotype: infants with more mature gut microbiota have higher levels of activity at night (waking up more often during the night). Additionally, their enterotype does not change from enterotype A to B between the ages of 6 and 12 months.

Sleep, brain and gut: all linked?

The brain activity analyzed using the nighttime electroencephalograms at the age of 6 months proved to be rich with useful findings. 

First finding: infants with predominantly Bifidobacterium flora showed less slow-wave sleep (“light sleep”);
Second finding: the quality of sleep at 6 months of age can be used to predict the bacterial diversity of the gut microbiota at age 1. The presence of more theta waves at 6 months is a sign that there will be lower bacterial diversity at 12 months.

Lastly, the gut microbiota at 6 months and above all sleep at 6 and 12 months of age predict the behavioral development of the child at 24 months.