Babies’ sleep already follows a well‑established rhythm

How do sleep cycles develop in the first months of life? An international study involving Grégory Hammad (Chronobiology Laboratory, GIGA – ULiège) provides new insights based on the analysis of more than 35,000 hours of sleep from 152 infants followed throughout their first year.

 

By using simple motion sensors worn on the ankle, a non-invasive method compatible with everyday family life, the researchers were able to observe a key phenomenon: babies’ sleep is structured by regular cycles of about one hour, already present from the age of three months. These cycles, comparable to the alternation between rapid eye movement (REM) and non-rapid eye movement (NREM) sleep in adults, gradually lengthen over the months.

 

“We show that these rhythms, which have long been difficult to study at large scale, can be observed simply through movement during sleep,” explains Grégory Hammad. “This opens the door to much larger studies to better understand sleep development and its links with health.”

 

The results reveal that these cycles increase on average from about 60 minutes in infants to longer durations over the first year, gradually approaching adult sleep cycles. This evolution is accompanied by increasingly consolidated sleep, with longer and less fragmented nights.

 

The study also highlights the potential influence of everyday factors, such as breastfeeding or sleep arrangements—on cycle duration. These findings suggest a complex interaction between biological maturation and environmental factors.

 

Beyond these results, the work illustrates the potential of wearable technologies to better understand infant sleep. By enabling long-term monitoring of large cohorts, these tools could help identify new developmental indicators and, ultimately, improve early detection of potential sleep-related issues. "The more we learn, the more we can pinpoint healthy from unhealthy sleep and help parents and doctors to catch problems early to support infants in their optimal development" says Prof Eva Winnebeck, from the University of Surrey (UK). 

 

For the researchers, one thing is clear: even very early in life, our sleep is already structured by fundamental rhythms, and their evolution may play a key role in a child’s development.