Air pol­lu­tion linked to greater risk of mouth can­cer, finds study

The Guardian Australia - - Front Page - Ni­cola Davis

High lev­els of air pol­lu­tion are linked to an in­creased risk of mouth can­cer, new re­search has re­vealed.

Sci­en­tists have pre­vi­ously linked high air pol­lu­tion 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.

Now re­searchers say that at very high lev­els of air pol­lu­tion, the risk of de­vel­op­ing mouth can­cer ap­pears to rise.

Writ­ing in the Jour­nal of In­ves­tiga­tive Medicine, re­searchers in Tai­wan de­scribe how they dis­cov­ered the as­so­ci­a­tion by look­ing at air pol­lu­tion data from 66 air qual­ity mon­i­tor­ing sta­tions around the coun­try col­lected in 2009, and comb­ing this with data from the health records of more than 480,000 men aged 40 and over from 2012/13. In to­tal, there were 1,1617 cases of mouth can­cer among par­tic­i­pants.

The team fo­cused on tiny par­tic­u­lates of pol­lu­tion known as PM2.5s, and took the men’s ex­po­sure to this air pol­lu­tion as be­ing based on where they lived. They then sorted the par­tic­i­pants into four groups, from low­est to high­est lev­els of ex­po­sure.

After tak­ing into ac­count fac­tors in­clud­ing age, ex­po­sure to ozone, lev­els of other par­tic­u­lates, age, smok­ing sta­tus and whether the men chewed be­tel quid – a mix­ture of in­gre­di­ents that in­cludes areca nut and be­tel leaf and is known to in­crease the risk of mouth can­cer – the re­searchers 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% greater odds of de­vel­op­ing the disease.

“The mech­a­nism through which this oc­curs is not clearly un­der­stood, hence fur­ther in­ves­ti­ga­tions are re­quired,” the re­searchers write.

The World Health Or­gan­i­sa­tion (WHO) has pre­vi­ously said av­er­age an­nual lev­els of PM2.5s should not ex­ceed 10 μg/m3. While in cen­tral Lon­don the av­er­age an­nual fig­ures have been found to be dou­ble this, they are still far lower than the high­est lev­els seen in the Tai­wanese study.

How­ever, many other cities around the world have ex­tremely high lev­els of air pol­lu­tion. Ac­cord­ing to fig­ures from the WHO, the av­er­age an­nual level of PM2.5s in Kabul is 86 μg/m3, while in Bei­jing it is 85 μg/m3 and in Delhi it has been recorded at 122 μg/m3.

But the study has lim­i­ta­tions, in­clud­ing that it is does not con­sider the men’s pre­vi­ous ex­po­sure to air pol­lu­tion over their life­time – which may have been higher or lower than their re­cent ex­po­sure.

Prof Frank Kelly, chair in en­vi­ron­men­tal health at King’s Col­lege Lon­don, who was not in­volved in the study, said it would be use­ful to ex­plore whether a link be­tween mouth can­cer and air pol­lu­tion is seen in other coun­tries.

“Air pol­lu­tion has pre­vi­ously been linked with sev­eral types of can­cer, in­clud­ing breast, liver, lung and pan­cre­atic can­cer. It is there­fore not sur­pris­ing that this new study in Tai­wan has made a pos­si­ble link with mouth can­cer,” he said. “How­ever, given that air pol­lu­tion con­cen­tra­tions and smok­ing in­ci­dence are much lower in the UK and we don’t chew be­tel all sug­gest that the in­creased risk of de­vel­op­ing mouth can­cer may be unique to Tai­wan.”

Air pol­lu­tion has pre­vi­ously been linked with sev­eral types of can­cer

Prof Frank Kelly, King's Col­lege Lon­don

Pho­to­graph: Matt Dunham/AP

Pol­lu­tion in cen­tral Lon­don is dou­ble the World Health Or­gan­i­sa­tion max­i­mum rec­om­mended lev­els, though lower than those in theTai­wanese study.

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