Daily full-body cryostimulation - exposure to extreme cold - improves sleep quality and mood in healthy young men and women, according to new research by scientists at Université de Montreal and Université de Poitiers, in France.
"The use of cold for therapeutic purposes goes back to ancient Greece," said Dupuy, an associate professor at UdeM's School of Kinesiology and Physical Activity Sciences. "But we still don't know the exact amount of cold needed to produce sleep benefits."
In a study published in the December issue of Cryobiology, Dupuy and his Poitiers colleagues Laurent Bosquet and Benoit Dugué describe having recruited nine women and 11 men, average age 23, to undergo daily cryostimulation sessions for five consecutive days.
The experiment was then repeated without cryostimulation to isolate its effects on sleep.
Each cryostimulation session consisted of spending five minutes in a chamber cooled to -90°C. "While in the chamber, the subjects wore underwear or a swimsuit and socks, croc-type shoes, mittens and a tuque to protect their extremities from the intense cold," said Dupuy.
Following the cryostimulation, the subjects went about their normal daily activities until bedtime, avoiding alcohol consumption and any activity, physical or otherwise, that could affect their sleep.
At bedtime, they were fitted with a wireless headband equipped with brain activity sensors, a wrist actigraph and a heart-rate sensor to measure the effects of cryostimulation on their physiology and sleep patterns.
Each morning, they completed a questionnaire to assess perceived sleep quality.
One session not enough
The data showed that one cryostimulation session was not enough to improve sleep: the benefits appeared only after five consecutive sessions.
"Our sleep architecture analysis revealed a significant increase in the duration of slow-wave sleep during nights following cryostimulation compared to nights without cryostimulation," said Dupuy. "Slow-wave sleep, considered the most restorative phase of sleep, increased by an average of 7.3 minutes during the first two sleep cycles."
The study also showed marked gender differences, with women benefiting from cryostimulation more than men. Women reported an improvement in perceived sleep quality on the third and fourth nights of the protocol, from an average of 3.4 on a scale of 1 to 5 without cryostimulation to 3.9 with cryostimulation, and their perceived level of anxiety decreased from 43 to 38.
"Women and men did not have identical responses," said Dupuy. "This suggests that the dose of cold should be adjusted according to gender, although this requires further study."
Although the changes observed may seem small, they are promising and could pave the way for a variety of applications, he added.
"While this study focused on people who generally sleep well, we believe that cryostimulation could be especially beneficial for people with sleep problems."
Other uses highlighted
And the potential uses don't stop there.
"For elite athletes, it could help with recovery, while for the general population it could help people with chronic inflammation or mild dementia when used in combination with physical exercise," said Dupuy.
The study was part of a larger research program on cryostimulation. Dupuy and his colleagues received funding to study its use by athletes preparing for the Paris Olympics in 2024 and two more scientific papers on the link between cold and sleep will be published soon.
Many issues remain to be explored, including the long-term effects of cryostimulation and the mechanism behind its clinical effects.
"But one thing is clear: this is not a placebo effect," said Dupuy. "Other studies have demonstrated similar positive effects in elite athletes."
In some countries, such as Poland, the cost of cryostimulation sessions is already covered by public health insurance plans. "With these encouraging new data, cryostimulation could well be adopted in clinical settings in the fields of medicine, kinesiology and physiotherapy," Dupuy concluded.
