Daily exposure to intense cold can improve sleep quality

Daily whole-body cryostimulation – exposure to extreme cold – improves sleep quality and mood in healthy young men and women, according to new research by scientists at the Université de Montreal and Université de Poitiers in France.

“The use of cold for therapeutic purposes dates back to ancient Greece,” says Dupuy, associate professor at UdeM’s School of Kinesiology and Physical Activity Sciences. “But we still don’t know exactly how much cold is needed to achieve sleep benefits.”

In a study published in the December issue of CryobiologyDupuy and his colleagues from Poitiers, Laurent Bosquet and Benoit Dugué, describe recruiting nine women and eleven men, with an average age of 23 years, 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 room, the subjects wore underwear or a swimsuit and socks, crocodile-style shoes, mittens and a tuque to protect their limbs from the intense cold,” Dupuy said.

After cryostimulation, subjects continued their normal daily activities until bedtime, avoiding alcohol consumption and any activity, physical or otherwise, that could affect their sleep.

Before bed, 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.

Every morning they completed a questionnaire to assess perceived sleep quality.

One session is not enough

The data showed that one cryostimulation session was not enough to improve sleep: the benefits only appeared after five consecutive sessions.

“Our sleep architecture analysis revealed a significant increase in slow-wave sleep duration during nights after cryostimulation compared to nights without cryostimulation,” says 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 clear gender differences, with women benefiting more from cryostimulation 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 anxiety level decreased from 43 to 38 .

“Women and men did not respond identically,” Dupuy said. “This suggests that the dose of cold should be adjusted according to gender, although this requires further research.”

While the observed changes may seem small, they are promising and could pave the way for a variety of applications, he added.

“Although this study focused on people who generally sleep well, we believe that cryostimulation could be especially beneficial for people with sleep problems.”

Other applications highlighted

And the potential applications don’t stop there.

“For elite athletes it could help recovery, while for the general population it could help people with chronic inflammation or mild dementia when used in combination with exercise,” Dupuy said.

The research was part of a larger research program into cryostimulation. Dupuy and his colleagues received funding to study its use by athletes preparing for the 2024 Paris Olympics. 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,” Dupuy said. “Other studies have shown similar positive effects in elite athletes.”

In some countries, such as Poland, the costs of cryostimulation sessions are already covered by public health insurance. “With these encouraging new data, cryostimulation could well be applied in clinical settings in the fields of medicine, kinesiology and physiotherapy,” Dupuy concluded.