Opening a window or door may help improve sleep, study finds

If you’re having trouble getting a restful night’s sleep, opening a bedroom window or door may help, according to a new study from the Netherlands.

The reason appears to be related to the fact that circulating air decreases the amount of carbon dioxide that builds up in our bedrooms as we breathe throughout the night. The study found a correlation between lower levels of carbon dioxide in bedrooms and deeper, more efficient sleep, as well as fewer awakenings during the night.

Any simple behavioral change that can improve sleep is welcomed news. Here in the United States, more than a third of us report not getting the recommended minimum of seven hours of sleep per night, according to the Centers for Disease Control and Prevention. That’s not good for our health. Insufficient sleep has been linked to a variety of health problems, including obesity, diabetes, high blood pressure, heart disease, various mood disorders, a greater susceptibility to infections, and even premature death. Too little sleep also leaves us more susceptible to accidents and mental errors, both on the job and off. 

Of course, many factors go into why people aren’t getting enough sleep, and opening a window or door is certainly not going to be enough to help everyone. But it may help some. That’s why the findings from this new study are interesting.

Setting up the study

For the study, researchers at the Eindhoven University of Technology recruited 17 healthy student volunteers. The participants were asked to sleep in their own bedrooms under two types of ventilation settings: one with all windows and doors closed and the other with a window or door open. Each setting lasted for five nights.

None of the participants had a history of sleep disorders or a medical condition that can affect sleep, such as asthma, and they all slept alone in their rooms. They were also instructed to abstain from alcohol and caffeine before going to bed.

The researchers measured the carbon dioxide levels, temperature, background noise and relative humidity in each of the participants’ bedrooms. They also had each participant wear devices that measured their sleep/wake patterns and movements during sleep.

In addition, the participants were asked to keep sleep diaries and to fill out questionnaires each morning about the quality of their sleep.

Key findings

The data revealed, as expected, that opening a window or door before going to bed reduced the carbon dioxide levels in the bedrooms. The average level of carbon dioxide in the “open” rooms was 717 ppm (particles per million), while the average level in the “closed” rooms was 1,150 ppm (and went as high as 3,000 ppm).

Further analysis of the data then uncovered a direct correlation between lower levels of carbon dioxide and the participants’ subjective assessment on the questionnaires of how soundly they had slept. When the carbon dioxide levels were low — when a window or door was open — the participants reported a more restful sleep.

The study’s objective measures backed up the participants’ self-assessments of how well they had slept. The devices worn by the participants showed that they slept more efficiently and woke up fewer times during the night when the room was better ventilated.

That finding held even though the average noise level was higher in the “open” bedrooms and the average temperature was slightly lower. (There was no significant difference in the absolute humidity of the “open” and “closed” rooms.)

The researchers also found that open windows led to better ventilation than open doors. But, as they point out in their paper, when people can’t sleep with an open window because of excess noise or cold (or perhaps for safety reasons), keeping a door ajar will still reduce carbon dioxide levels.

Limitations and implications

This study comes with plenty of caveats. To begin with, it involved a small number of volunteers, all of whom were young Dutch students. The findings may not be applicable to other population groups. 

The participants were also aware that they were being asked to sleep under two different sleeping environments, a factor that may have influenced their subjective assessment of how well they slept.

Yet another limitation is that the study took place during the months of October, November and December, when the outdoor temperatures were relatively cold. The findings might be different when temperatures (and humidity) are higher.

Still, the findings of this study support other research that has pointed to lower levels of carbon dioxide “improving self-assessed sleep quality, subjective perception of air, better wakefulness and ability to concentrate on the day after, and better … sleep efficiency,” the study’s authors write.

So, if you find yourself sleeping fitfully, you might want to try cracking open a window or door.

FMI: The study was published in the journal Indoor Air, where it can be read in full. You’ll also find a comprehensive list of other “sleep hygiene” practices for getting a better night’s sleep on the National Sleep Foundation’s website.