A phone placed near the bed may hold an unexpected indicator of the air quality outside the window. Researchers used audio recordings collected by a sleep app to test the relationship between air pollution and nighttime coughing and found a clear correlation between elevated levels of fine particles and increased coughing fits.
The study, which involved researchers from Cambridge University, Tsinghua University and Sleep Cycle, analyzed passively recorded cough sounds via the phone microphones of app users in 32 cities across 12 countries over a period of approximately 500 days, collecting data at the city level without relying on a single individual''s recording.
After taking into account factors such as weather and influenza prevalence, the researchers found that every 10 micrograms per cubic meter increase in PM 2.5 particle concentration was associated with an increase of approximately 2.4% in the rate of nighttime coughing.
The increase was also observed even at relatively low pollution levels.
But the researchers stress that the study is observational, meaning it reveals a correlation but does not prove on its own that pollution is the direct cause of every cough. Cambridge University said the result opens the door to using everyday phones and apps to monitor mass health indicators related to the environment on a large scale.