Nodding off in the middle of the day may be down to pollution generated by traffic, suggests new research.
The study shows exposure to traffic pollution is a trigger for daytime sleepiness - and may also trigger SNORING.
More than 12,000 adults were included in the Respiratory Health in Northern Europe (RHINE) study.
The findings show that people exposed to high levels of pollution had a 65 per cent greater chance of suffering from daytime sleepiness, compared to those who had no exposure.
Traffic noise in the bedroom was also a trigger - with people 46 per cent more likely to feel sleepy in the day if exposed.
And the research also suggests that people are also 29 per cent more likely to be a habitual snorer if they are exposed to traffic noise while they sleep.
Daytime sleepiness affected one in five people involved in the study, while one in four reported habitual snoring.
Ane Johannessen, an epidemiologist at Bergen University in Norway, wrote the study together with Professor Thorarinn Gislason and other Northern European researchers.
She said: “Exposure to traffic should be taken into account when planning treatment for patients with sleep disturbances, because reducing noise and pollution exposure in the bedroom may have a beneficial effect.
“Reducing exposure through relocating the bedroom away from pollution sources or making the bedroom more soundproof to protect against traffic noise, as well as mapping alternative and less polluted outdoor everyday routes may help patients with their sleep disorders.”
The study also showed that men, older subjects, smokers and those with lower education were more likely to report habitual snoring.
They were usually less physically active, with a higher BMI, and more likely to have a diagnosis of obstructive sleep apnoea (OSA).
Women, older people, smokers, and those with lower education were more likely to report daytime sleepiness.
The new research is due to be presented at the European Respiratory Society’s International Congress in London next month.
Professor Jorgen Vestbo, President of ERS and Professor of Respiratory Medicine at the University of Manchester, said: “The question of who snores may be a running joke in some households but for many snoring is a serious issue, with direct links to physical and mental well being and the same is true for daytime sleepiness.
“We want people to think more about the environment around them and the impact it can have - from the way they sleep to the air they breathe.”
To coincide with Congress, the ERS will be holding some free public lung function testing, starting in Trafalgar Square on September 2 and 3.