From our youngest days, calming words have helped us drift off to sleep, and many adults still find guided meditations and gentle bedtime stories a peaceful way to nod off. According to new research, the calming effect of words can extend beyond wakefulness to positively impact our sleep. Scientists found that words like “relax” and “easy” have a soothing effect while you’re asleep that’s tied to a slower heart rate, better sleep quality, and waking up feeling more well rested.  

Researchers at the GIGA Center of Research Cyclotron in Belgium partnered with colleagues from the University of Fribourg in Switzerland to better understand how the body’s reactions to calming words impacted sleep by analyzing heart rate data. 

The study built on previous research that established that slow-wave sleep lengthened and the quality improved when relaxing words were played during non-rapid eye movement sleep (NREM).

Slow-wave sleep, also known as deep sleep, is the third NREM sleep stage associated with slowed breathing, relaxed muscles, as well as memory and immune function. Sufficient slow-wave sleep is integral to waking up feeling refreshed. 

With the effect of calming words on the mind established, the researchers hoped to take the findings a step further. Noting that other studies found heart rate variability could be used as a way to study the sleeping brain, they planned to analyze heart rate data collected during sleep. Their aim: determining to what extent the sleep-improving effect of relaxing words on the mind might also be connected to calming effects on the body. 

To test their hypothesis, the researchers analyzed electrocardiography (ECG) data collected during a standard lab-based sleep study. They compared the interval between heartbeats on nights when relaxing words were played during sleep to nights when neutral words were played. 

On the nights sleepers experienced the calming words, the heartbeat interval was longer, indicating a slower heart rate and a more relaxed body. 

The researchers then used data models to corroborate the interaction between cardiac and brain activity and their associated effect on slow-wave sleep. The results suggested that the body and mind effects were not independent but share an integrated relationship that resulted in the positive changes relaxing words have on slow-wave sleep.   

This connection between outside stimuli and sleep health offers new opportunities for scientists. In particular, the study authors advocate for more sleep studies that use a systemic approach to sleep, measuring impacts on both the mind and body. 

For sleepers, this whole-body perspective could lead to new therapies focused on comprehensive sleep health and pave the way for the regular use of soothing sleep-time recordings aimed at improving overall well being.

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3 Sources

  1. Koroma, M., Beck, J., Schmidt, C., Rasch, B., & Demertzi, A. (2024). Probing the embodiment of sleep functions: Insights from cardiac responses to word‐induced relaxation during sleep. Journal of Sleep Research.
  2. Beck, J., Loretz, E., & Rasch, B. (2021). Exposure to relaxing words during sleep promotes slow-wave sleep and subjective sleep quality. SLEEP, 44(11).
  3. Chouchou, F., & Desseilles, M. (2014). Heart rate variability: A tool to explore the sleeping brain? Frontiers in Neuroscience, 8.

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