A new study in the United States has revealed that people who smoke one pack of cigarette a day develop an average of 150 extra mutations in their lungs every year.
The study released on Sunday in Washington explained why smokers had a higher risk of developing lung cancer.
Ludmil Alexandrov, from Los Alamos National Laboratory and co- author of the report, said in a statement that apart from lungs, other organs were also affected by smoking.
He said with the study showed that a pack of cigarette a day led to an estimated average 97 mutations in each cell in the larynx, 39 for the pharynx, 23 for mouth, 18 for the bladder, and six in every cell of the liver, each year.
“Before now, we had a large body of epidemiological evidence linking smoking with cancer, but now we can actually observe and quantify the molecular changes in the DNA due to cigarette smoking.’’
Alexandrov, however, said the findings published in the U.S. Science Journal, revealed that cigarettes contain more than 7,000 chemicals, including over 70 known to cause cancer.
He said previous studies had associated cigarette smoking with increased risk for 17 different types of cancer, including cancer in tissue not directly exposed to smoke; it has remained unclear how smoking causes cancers.
Alexandrov said for this study, researchers looked at over 5,000 tumours, comparing cancers from smokers with cancers from people who had never smoked.
“They found particular molecular fingerprints of DNA damage called mutational signatures in the smokers’ DNA, and they counted the number of these particular mutations in different tumours.
“The study revealed at least five distinct processes of DNA damage due to cigarette smoking,’’ he said.
Alexandrov said the most widespread of these is a mutational signature already found in all cancers, which “seems to accelerate the speed of a cellular clock that mutates DNA prematurely’’.
Prof. Mike Stratton, joint lead author from Wellcome Trust Sanger Institute, explained that the research had indicated that the way tobacco smoking causes cancer is more complex than we thought.
“The genome of every cancer provides a kind of archaeological record written in the DNA code itself of the exposures that caused the mutations that lead to the cancer,”
Stratton said that tobacco smoking claims the lives of at least six million people every year.