Our sleep is strongly influenced by the bedroom environment. Excessive heat and cold, light pollution and noise can all harm sleep — as can uncomfortable bedding and even a messy bed!
Since we already know that air pollution and household mold can harm sleep, it makes sense that poor bedroom air quality might make sleep more difficult, too. To determine whether this is the case, researchers examined the effects of bedroom air quality on sleep and next-day performance by conducting two experiments.
The open window experiment
Participants slept in a room with sealed external air vents for two weeks. For one week, a window was left open by four inches. For another week, participants could open or close the window as they wished. Participants were allowed to use an electric heater located below the window to achieve their preferred room temperature and could choose their preferred sleepwear and bedding for the entire two weeks.
The ventilation experiment
In the second experiment, participants again slept in a room for two weeks. For one week, the air vent in the room was removed and replaced with a fan that supplied outdoor air to the room whenever levels of carbon dioxide rose above 900 ppm. For the other week, the fan was switched off and the air intake hole was sealed closed. Windows were kept closed during the night for the entire two weeks, but participants could open or close them during the daytime as they wished.
For both experiments, instruments in the room measured air temperature, relative humidity and carbon dioxide levels. Sleep quality was measured using questionnaires and a wrist actigraph, while daytime performance was measured using the Tsai-Partington numbers test and Baddeley's Grammatical Reasoning Test.
Participants were also asked to rate their sleep environment based on perceived air quality, symptoms of sick building syndrome, perceived sleep quality, and next-day symptoms. Questions were also asked about clothing worn during sleep, number of awakenings, reasons for any awakenings, and bedtime and wake times. All questionnaires and tests were administered within 10 minutes of waking up in the morning.
How bedroom air quality affected sleep
In the open window experiment, participants reported that they found it easier to fall asleep and that they felt less sleepy the following day when the window was left open at night. Objective sleep data from the wrist actigraphs confirmed that participants fell asleep significantly faster when the window was left open at night.
In the ventilation experiment, participants reported feeling more well rested and less sleepy the following day when the ventilation fan was switched on - but they reported more mouth and skin dryness. Data from the wrist actigraphs found that sleep efficiency was significantly better when the fan was in operation.
The authors of the study also reported that data suggested next-day performance may be better after sleeping in rooms with better air quality.
What does this all mean?
This study demonstrated that bedroom air quality can influence sleep and may also influence next-day performance when it comes to cognitive tasks. Outdoor air inlets can improve ventilation and air quality, and this can improve sleep quality. If you live in a quiet area with minimal pollution, the simple act of opening a window at night will improve ventilation and bedroom air quality, and may improve the quality of your sleep.