Do you sleep more soundly when you leave your windows open during cooler weather? It isn’t your imagination—research shows that people may get better-quality sleep when fresh air circulates in the bedroom.

A recent study published in the journal Indoor Air found that when people slept in rooms with ventilation—either with an open window or open door—compared to an unventilated room, their sleep improved, they woke up fewer times per night, and carbon dioxide levels in the room were lower. As carbon dioxide levels decreased, people slept more soundly and their awakenings decreased.

“Carbon dioxide levels are taken as a proxy of how good the air quality is,” says study author Asit Kumar Mishra, PhD, a postdoctoral researcher with the Berkeley Education Alliance for Research in Singapore. “Higher carbon dioxide levels imply poorer ventilation. This, in turn, would imply an increase in other pollutants in the room as well. The impact on sleep could be as a result of the increase in levels of multiple indoor pollutants. In a manner, it is similar to how occupant performance reduces when they have to work in buildings with less than optimal ventilation.”

Other research has shown that rooms ventilated by open windows or air-intake fans had lower carbon dioxide levels, and people who slept in such rooms reported feeling better-rested the next morning, with improved concentration levels. They also scored better on logic tests than people who had slept in unventilated rooms.

This may be because ventilated rooms are likely to contain more oxygen, which may be linked to better cognition. “Our brain… requires energy at any time of the day, including during sleep, because this is when memory formation and information processing happens,” says Eva Cohen, a certified sleep science coach with Kansas-Sleep in Kansas City, Kansas.

“When we produce energy, we utilize both glucose and oxygen during a chemical reaction called glycolysis. [A] lack of oxygen in the air can make the glycolysis slower, thus putting the brain in ‘hungry mode’ and interfering with its work.”

Researchers haven’t yet studied the effects of fresh air on sleep quality and athletic performance, but some experts believe that nighttime exposure to fresh air may positively impact physical performance, in addition to cognitive performance.

“The effect of sleep on exercise is an evolving field of study, but research suggests that sleep plays an important role in athletic performance,” says Paul Reehal, MD, a Las Vegas-based sports medicine specialist and consultant for Sleepline. “Sleeping in a room with an open window may lead to better workouts by improving air circulation and providing a cool sleep environment.”

You can try sleeping with your windows open for a few nights to see if it impacts your sleep quality. “It’s best to open windows a bit, but not too wide, to minimize entry of noise and light,” Reehal says. “Opening more than one window will allow for better air circulation.”

Sleeping with an open window isn’t ideal in every circumstance. During hot weather, it may make your bedroom uncomfortably warm, which could interfere with sleep quality. And if you live near train tracks, a flight path, or a fire station, keeping your window open would allow more noise than usual into your room—and noises like these may disrupt your sleep, according to research.

If you don’t want to open your bedroom window because of the heat or noise outside, leave your bedroom door open when you go to sleep instead. “Our findings suggested that opening a door, while not as good as opening a window in terms of the carbon dioxide levels maintained, still provided similar quality of sleep,” Mishra says. “Leaving the bedroom door open even slightly keeps the bedroom air connected with the larger house air, and thus, [a] rise in any indoor pollutant level is much slower.”