Study links air pollution, heat, carbon dioxide, and noise to reduced sleep

Air pollution, a warm bedroom, and high levels of carbon dioxide and ambient noise may all adversely affect our ability to get a good night’s sleep, suggests a study from researchers with the Perelman School of Medicine at the University of Pennsylvania and the University of Louisville.

The study, published today in Sleep Health, is one of the first to measure multiple environmental variables in the bedroom and analyze their associations with sleep efficiency—the time spent sleeping relative to the time available for sleep. The analysis found that in a group of 62 participants tracked for two weeks with activity monitors and sleep logs, higher bedroom levels of air pollution (particulate matter <2.5 micrometers or PM_2.5), carbon dioxide, noise, and temperature were all linked independently to lower sleep efficiency.

“These findings highlight the importance of the bedroom environment for high-quality sleep,” said study lead author Mathias Basner, MD, Ph.D., professor and director of the division of Sleep and Chronobiology in the department of Psychiatry at Penn Medicine.

In addition to work and family obligations that compete with sleep for time, a quickly changing environment due to growing urbanization and climate change seems to have made it harder to get a good night’s sleep. Sleep that is of inadequate duration, or inadequate efficiency due to frequent disruption (“tossing and turning”), affects work productivity and quality of life.

It also has been linked to a higher risk of chronic diseases including heart disease, type 2 diabetes, depression, and dementia. This research is among a limited number of studies that looked at associations between multiple objectively measured factors in the sleep environment—such as noise and temperature—and objectively measured sleep.

The study was a collaboration between Penn Medicine and the Christina Lee Brown Envirome Institute of the University of Louisville, which is led by Aruni Bhatnagar, Ph.D.. The researchers recruited participants from the National Institutes of Health Green Heart Project that investigates the effects of planting 8,000 mature trees on the cardiovascular health of Louisville residents.

For each of the environmental variables measured, the researchers compared sleep efficiency during exposures to the highest 20 percent of levels versus lowest 20 percent of levels. Through this analysis, they found that high noise was associated with a 4.7 percent decline in sleep efficiency compared to low noise, high carbon dioxide with a 4.0 percent decline compared to low levels, high temperature with a 3.4 percent decline compared to low temperature, and high PM_2.5 with a 3.2 percent decline compared to low PM_2.5. Two other sleep environment variables, relative humidity and barometric pressure, appeared to have no significant association with sleep efficiency among the participants.

Interestingly, only bedroom humidity was associated with sleep outcomes assessed with questionnaires, such that higher humidity was associated with lower self-reported sleep quality and more daytime sleepiness. This suggests that studies based on questionnaires may miss important associations readily detected by objective measures of sleep. This is not surprising as humans are unconscious and unaware of themselves and their surroundings during large portions of their sleep period.

Also, most study participants rated humidity, temperature and noise levels in the bedroom as “just right” regardless of the actual exposure levels.

“We seem to habituate subjectively to our bedroom environment, and feel there is no need to improve it, when in fact our sleep may be disturbed night after night as evidenced by the objective measures of sleep we used in our study,” said Basner.

The researchers suggest that more research is needed now on interventions that could improve sleep efficiency by reducing exposures to these sleep-disrupting factors.

“This could be as simple as leaving a bedroom door open to lower carbon dioxide levels, and using triple-pane windows to reduce noise,” Bhatnagar said. “We also applied for funding that will allow us to investigate whether planting trees can improve sleep and cardiovascular health through improving health behaviors and the bedroom environment.”