Bad for DNA (Photo : Getty Images)
Smoking has been found to damage a smoker's DNA and, in some cases, this altered DNA can trigger cancer and other diseases.
The link between smoking and DNA damage is explained in a study of 16,000 people over the past 45 years by the Harvard Medical School and Hebrew SeniorLife, a rehabilitation center in Boston, Massachusetts that also conducts research into aging. The study was published in the American Heart Association journal Circulation: Cardiovascular Genetics.
Heart disease and cancer are both caused by genetic damage. Smoking is one of the biggest culprits in both diseases.
Smoking is the biggest cause of preventable illness, killing some 480,000 Americans every year through cancer, heart disease, lung disease and other illnesses, according to the U.S. Centers for Disease Control and Prevention. Smoking kills about six million people worldwide every year.
Researchers reported that smoking damages DNA in clear patterns in a process called "methylation." This process alters DNA and can inactivate a gene or change how it functions. Researchers said one result of methylation is that it causes cancer and other diseases.
They did, however, note most (but not all) of the damage fades over time. But some of this damage appears to remain forever.
"Our study has found compelling evidence that smoking has a long-lasting impact on our molecular machinery, an impact that can last more than 30 years," said Roby Joehanes of Hebrew SeniorLife and Harvard Medical School.
"The encouraging news is that once you stop smoking, the majority of DNA methylation signals return to never-smoker levels after five years, which means your body is trying to heal itself of the harmful impacts of tobacco smoking."
The team analyzed blood samples from 16,000 people that participated in different studies dating back to 1971. In all the studies, people gave blood samples and filled out questionnaires about smoking, diet, lifestyle and their health histories.
They found smokers had a pattern of methylation changes affecting over than 7,000 genes or one-third of known human genes. Many of the genes had links to heart disease and cancers known to be caused by smoking.
Among those who stopped smoking, most of these changes reverted to the patterns seen in people who never smoked after about five years. Smoking-related changes in 19 genes, including the TIAM2 gene linked to lymphoma, lasted 30 years, said the study.
"These results are important because methylation, as one of the mechanisms of the regulation of gene expression, affects what genes are turned on, which has implications for the development of smoking-related diseases," said Dr. Stephanie London of the National Institute of Environmental Health Sciences, who directed the team.
"Equally important is our finding that even after someone stops smoking, we still see the effects of smoking on their DNA."
