Consuming a pack of cigarettes every day for a year can cause multiple changes in cells within various parts of the body, according to the study.
The cells in parts of the body that are directly exposed to smoke are particularly damaged, with 150 mutations found to occur in lung cells within one year, 97 in the larynx and 39 in the oral cavity.
“Tobacco smoking damages DNA in organs directly exposed to smoke as well as speeds up a mutational cellular clock in organs that are both directly and indirectly exposed to smoke”, said Ludmil Alexandrov of the Los Alamos National Laboratory in Los Alamos, New Mexico, who led the study.
The study also shed light on how smoking can lead to cancer in organs that lie far from the smoke-exposed lungs, throat and mouth. “Some of them reflect direct damage to DNA,” Alexandrov says, “where you inhale the smoke and the smoke’s constituents bind to the DNA and they mutate it. We also found in organs not directly exposed to inhaled smoke, tobacco smoking is disregulating key cellular processes.”
Cells tend to accumulate more mutations as they divide and age. So, by increasing the number of mutations, smoking is basically aging your cells. In smoking-related bladder, liver and stomach cancers as well as other cancers where the organ isn’t exposed to smoke smoking still accelerates a “molecular clock” that normally would “tick” regularly with age, adds Alexandrov.
In other words, it accelerates the occurrence of genetic mutations, increasing the risk of cancer.
Cancer is caused by mutations in the DNA of a cell, and tobacco smoke contains more than 70 chemicals known to cause cancer, the researchers added.
Joint lead author Mike Stratton, a professor from the Wellcome Trust, said the findings show that mechanisms by which smoking causes cancer may be more complex than 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 cancer,” Stratton explained. “This study of smoking tells us that looking in the DNA of cancers can provide provocative new clues to how cancers develop and thus, potentially, how they can be prevented.”
The results “reveal a picture of direct and indirect effects,” said David Phillips, professor of environmental carconigenesis at Kings College London, who also conducted the research, in a statement.
The findings were published Nov. 4 in the journal Science.