Trouble Sleeping? Air Pollution Could Be the Culprit

A woman lays awake in bed, looking at a clock.
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The air pollution around you could affect how well you sleep, a new study finds.

Researchers found that people in the study who lived in areas with high levels of air pollution were 60 percent more likely to sleep poorly, based on the measures used in the study, than those who lived in areas with cleaner air.

Chronic sleep deprivation has been linked with a range of health problems, the study said.

"Not having enough sleep and having low quality sleep affects people's performance, increases the risk of vehicle accidents, lowers mood," said Dr. Martha E. Billings, the lead author of the study and an assistant professor of medicine at the University of Washington. [5 Surprising Sleep Discoveries]

"Over time, there is a higher risk of cardiovascular diseases and cancer in people who are not getting adequate sleep, so there is a lot of implications as well as general well-being and the quality of life," Billings said.

The researchers used data from an ongoing study called the Multi-Ethnic Study of Atherosclerosis (MESA) to look for correlations between exposure to air pollution and the quality of sleep of 1,863 individuals in six U.S. cities. The researchers focused on two measures of sleep quality — sleep efficiency, which is the total amount of time actually spent asleep, and the frequency of awakenings after falling asleep.

The study participants wore actigraphy watches, which are similar to a FitBit. They detected how many times each person woke up during the night and how long they stayed awake, Billings said.

The researchers compared this data set with information about the concentrations of two major air pollutants around the participants' homes. They looked at nitrogen dioxide (NO2) and fine particulate pollution (PM2.5), meaning solid particles in the air that have a diameter of less than 2.5 micrometers. This information came from the Environment Protection Agency's monitoring sites across the U.S. in combination with local environment data and statistical modeling.

The researchers grouped the participants into quartiles based on the level of air pollution in their areas, Billings said. "We found that there was an about 60 percent higher odds of having a low sleep efficiency if you had an exposure in the highest quartile of air pollution."

Low sleep efficiency, as the researchers defined it in the study, meant being asleep less than 88 percent of the time spent in bed. The researchers found that the percentage of people suffering from low sleep efficiency as well as the total amount of time they were awake increased with the concentration of air pollution in their homes.

The study found an association, not a cause-and-effect relationship, between air pollution levels and sleep quality. Billings said the researchers don't know how air pollution may affect sleep, but there are many possible mechanisms in which air pollution could be causing people to toss and turn. [7 Strange Facts About Insomnia]

"It may be because they are exposed to more traffic noise that is disrupting their sleep," Billings said. "It could also be an effect of the air pollution itself that is causing airway irritation. Sometimes those small particles can get into the blood stream and that could affect regulation of sleep in the brain – that's our hypothesis, but we still need further studies to show whether this is really the case."

The average age of the study's participants was 68. Billings said she and her team made sure to adjust for other factors that could affect people's sleep quality, such as body mass, age, smoking or having certain conditions, including sleep apnea or depression.

Air pollution has been linked to the increased risk of respiratory conditions, including asthma and even lung cancer. But recent studies have pointed to the possible association between air pollution and a much wider range of health problems. For example, a study by researchers at the University of Birmingham in the U.K. published earlier this year found that every extra 10 micrograms of PM2.5 per cubic meter of air was linked with a 22 percent increase in risk of dying of any type of cancer in elderly people.

Other research suggests that pregnant women who breathe highly polluted air are more likely to give birth prematurely, according to the Stockholm Environment Institute. A team from the University of Lancaster in the U.K. found air pollution particles in human brains, and said the evidence suggests these particles could contribute to dementia.

Billings and her colleagues presented their new research at the International Conference of the American Thoracic Society earlier this week. The findings have not been published in a peer-reviewed journal.

Originally published on Live Science.

Tereza Pultarova
Live Science Contributor
Tereza is a London-based science and technology journalist, video producer and health blogger. Originally from Prague, the Czech Republic, she spent the first seven years of her career working as a reporter, script-writer and presenter for various TV programmes of the Czech national TV station. She later took a career break to pursue further education and added a Master in Science from the International Space University, France, to her Bachelor's degree in Journalism from Prague's Charles University. She is passionate about nutrition, meditation and psychology, and sustainability.