Higher levels of air pollution may be linked to a heightened risk of developing oral cancer, which includes cancers of the lips, tongue, cheeks, floor of the mouth, hard and soft palate, a study has found.
While mouth cancers have been associated with smoking, drinking, human papilloma virus, and the chewing of betel quid ("paan"), the study added to this list increased levels of fine particulate matter (PM2.5) and to lesser extent, ozone.
"This study, with a large sample size, is the first to associate oral cancer with PM2.5... These findings add to the growing evidence on the adverse effects of PM2.5 on human health," said researchers including Shou-Jen Lan, Professor at the Asia University, in Taiwan.
Exposure to heavy metals and emissions from petrochemical plants are also thought to be implicated in the development of the disease while PM2.5 is known to be harmful to respiratory and cardiovascular health.
Previously, high air pollution has been linked to a host of health problems, from an increased risk of dementia to asthma and even changes in the structure of the heart, with recent research suggesting there is no "safe level" of air pollution.
For the new study, published in the Journal of Investigative Medicine, the team discovered the association by looking at air pollution data from 66 air quality monitoring stations in Taiwan, collected in 2009.
They combined this with data from the health records of more than 4,80,000 men aged 40 and over from 2012-13. In total, there were 11,617 cases of mouth cancer among the participants.
They found that men exposed to the highest levels of PM2.5s had an increased risk of mouth cancer.
Compared with men exposed to average annual PM2.5 levels of 26.74 micrograms (µg) per cubic metre (m3) of air, those exposed to concentrations of 40.37 µg/m3 or higher had 43 per cent greater odds of developing the disease.
A significant association was also observed for ozone levels below 28.69-30.97 parts per billion.
According to the World Health Organization (WHO), air pollution is responsible for an estimated 4.2 million premature deaths worldwide per year.
Around 6,57,000 cases of oral cancer are diagnosed annually across the globe, with 3,30,000 of those patients dying, it said.
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