Closing Bedroom Door at Night: How It Impacts Sleep & Performance

The simple act of sleeping with the door open or closed may have a surprisingly significant impact on sleep quality and cognitive function, according to recent research. A study conducted by the Technical University of Denmark (DTU) investigated how bedroom air quality influences both nighttime rest and daytime mental performance.

How Bedroom Ventilation Impacts Sleep

The research, which included experiments in climate chambers and real-world bedrooms in Denmark and Belgium, combined laboratory studies, field research, and controlled interventions. Researchers measured both objective and subjective indicators of sleep to determine the effects of ventilation. The findings suggest that inadequate ventilation, indicated by elevated carbon dioxide (CO₂) levels, can negatively affect sleep.

Specifically, the study found that increasing CO₂ concentrations – from an average of 800 parts per million (ppm) to as high as 1,700 ppm – was associated with increased sleep latency, meaning it took participants longer to fall asleep. It also led to a reduction in deep sleep.

“The quality of air in your bedroom can affect your cognitive abilities, such as your capacity for concentration, comprehension, and reaction,” explains Pawel Wargocki, an associate professor at DTU Sustain. “Sleeping in a well-ventilated room benefits your cognitive skills.”

CO₂ Levels and Cognitive Performance

Beyond sleep stages, the study also revealed a link between bedroom ventilation and cognitive performance. Participants demonstrated improved cognitive function after nights spent in better-ventilated rooms. Objective tests administered the following morning showed improvements when individuals had slept in environments with lower CO₂ concentrations.

In one field study, when average CO₂ levels rose from 856 ppm to 1,927 ppm, participants experienced less deep sleep, more light sleep, and more frequent awakenings during the night. Another analysis showed that increasing CO₂ from 812 ppm to 1,369 ppm also significantly reduced deep sleep.

Conversely, when bedrooms were ventilated by opening windows, reducing the average CO₂ concentration to around 761 ppm, sleep duration increased, and cognitive performance improved the next day.

Ventilation Recommendations and Practical Considerations

The research measured the rate of CO₂ emission during sleep – approximately 11 liters per hour per healthy adult – a crucial factor for designing effective ventilation systems. Based on these findings, the study recommends a ventilation rate of roughly 10 liters per second per person during sleep. For a typical 32 square meter bedroom, this translates to an air exchange rate of approximately 1.1 air changes per hour.

Current median air exchange rates in Danish bedrooms were found to be lower, at 0.4 air changes per hour, falling short of more stringent European standards which recommend up to 0.7 air changes per hour.

While opening windows can be an effective strategy for reducing CO₂, volatile organic compounds (VOCs), and particulate matter when mechanical ventilation isn’t available, researchers caution that this approach must consider potential drawbacks. These include external noise, urban pollution, and thermal discomfort.

Safety First: The Importance of a Closed Door

While ventilation is important, it’s crucial to remember the significant safety benefits of keeping a bedroom door closed at night. Closing the door acts as a barrier to slow the spread of fire and, more importantly, toxic smoke. In a fire, every second counts, and a closed door can provide valuable time for escape or rescue.

Study Limitations and Future Research

The researchers acknowledge certain limitations to their study, including a relatively small number of participants in some experiments and a focus on healthy adults without chronic sleep disorders. These factors limit the generalizability of the findings. However, the research contributes valuable insights into the impact of nighttime ventilation on health and underscores the importance of air quality even during sleep.

The study highlights that while CO₂ isn’t necessarily the direct cause of the observed effects, it serves as an indicator of ventilation quality and the presence of bioeffluents – compounds released during human respiration. Maintaining good ventilation practices, alongside prioritizing fire safety by keeping bedroom doors closed, can contribute to both better sleep and improved cognitive function.