Researchers say ventilation in a room can reduce carbon dioxide levels and help you sleep more soundly. It might be as important as room temperature.

Open your windows and doors.

A new study from the Eindhoven University of Technology in the Netherlands suggests those simple steps prior to going to bed can reduce carbon dioxide levels and improve sleep quality.

The study found that opening windows and doors improved ventilation and airflow in bedrooms. It improved the quality of sleep in 17 healthy participants.

“What we expected to observe was that lower ventilation levels would negatively affect sleep. Though we were not able to find a clear distinction across all parameters measured, the indication was that lower ventilation rates are likely to affect sleep quality negatively,” Dr. Asit Mishra, a study author with the Eindhoven University of Technology, told Healthline.

The authors found that the decrease in carbon dioxide levels when windows and doors were open improved the number of awakenings and sleep efficiency.

Mishra explained that in studies of this nature, carbon dioxide is used as an indicator of ventilation levels.

“The logic being that under normal conditions, the sole source of CO2 inside are human beings,” he said. “From CO2 levels we can have a pretty clear idea regarding ventilation levels, and if the ventilation levels are not good enough, it would indicate that there are likely to be other pollutant species indoors.”

Mishra added that as per current standards, when carbon dioxide levels reach 1,200 parts per million (ppm), “the ventilation levels have become poor enough that occupants will start to perceive them, and their productivity/focus can be affected negatively.”

Subjective measure of sleep quality was recorded through questionnaires and sleep diaries.

Actigraphy, a sensory method of monitoring rest-activity cycles, monitored subjects during sleep.

To measure sleep quality, participants wore a SenseWear armband to measure skin temperature, heat flux, bed microclimate temperature, and skin moisture levels.

The armband also logged the length of sleep and number of awakenings.

Additionally, a flex sensor was placed under the participants’ pillows to track their movements during the night. These movements may indicate restlessness during sleep.

According to the study, published in the journal Indoor Air, about a third of an average person’s life is spent asleep, and sleep environments often have poorer ventilation rates compared to our typical living environments.

This is because a sleep microenvironment comprises of the pillow, mattress, bedding, and other things.

The air volume is trapped between the covers and the body of the person sleeping.

“This is the environment which potentially contains a diverse profile of pollutants and to which we are all exposed to for nearly a third of our life, creating significant exposure risks,” Mishra said.

“We spend a considerable portion of our life in bed. However, bedroom ventilation and pollutants in bedroom are not a very well-explored subject. There needs to be an awareness that in the confined environs of a bed, without proper ventilation, we are likely to expose ourselves to a myriad variety of pollutants,” he added.

James B. Maas, PhD, chief executive officer of Sleep for Success and author of “Power Sleep,” commends the authors of the study, as it will encourage further research in the field.

“I applaud the investigators’ research as to the methodological issues encountered in trying to subjectively and objectively measure variables that might influence sleep quality. Their finding that lower CO2 levels can produce better sleep depth, sleep efficiency, and lesser number of awakenings has significant application for engineering design of bedroom ventilation,” he told Healthline.

Maas said there’s some disagreement in the field as to the best room temperature for great sleep, but he added that “the authors smartly point out the important variable might well be the bedding microclimate temperature.”

According to Maas, sleep researchers for years have recommended temperature for bedrooms be between 67 and 70ºF (19.4 and 21ºC).

Most recent research suggests 65 to 67ºF (18.3 to 19.4ºC) might be better.

“However, microclimate temperature might be the most important variable because it most accurately measures close to the body,” Maas said. “A cold room temperature does not take into account the number of blankets/comforters you have, your pajama warmth, and your sheets environment from being too hot or cold.”

Maas added that there’s a company in Colorado “that is called 37.5 (which is normal body temperature as measured in Celsius). They produce materials that can be used in sheets and pillowcases, as well as in nightwear, to keep your body at, or very close to, 98.6 Fahrenheit.”

If you’re concerned about security, outdoor pollution, or cold weather, Mishra advises to keep your bedroom door open.

“Keeping the door open lessens chances of CO2 levels rising too high,” he said. “During summer, if you can keep both door and a window open, the cross ventilation at night can also help in improving indoor thermal conditions.”

While opening windows improves ventilation better than opening doors, Mishra said they observed that “opening doors still improves ventilation levels enough that the room conditions are closer to the levels where sleep is less likely to be affected due to ventilation.”

According to Mishra, the researchers are “certainly aiming toward conducting further studies which can have larger number of participants.”

He added that “the current work was an exploratory task undertaken to get a validation of the proposed methodology. The tough task right now is to get appropriate funding for these plans.”

He confirmed that all 17 participants were healthy individuals and that the questionnaires didn’t suggest any sleep trouble prior to the study and over the course of the study. However, Mishra plans on branching the study out to susceptible subjects.

“We also want to focus on specific subpopulations that are more vulnerable… such groups could be elderly people with dementia/Alzheimer’s and young children with breathing disorders,” he said.

Mishra added, “We hope such studies lay the foundation for moving towards a regimen where preventive, instead of curative, action can be taken to ensure good sleep quality and hence well-being and health.”