Smoking affects human genomes - a complete set of DNA in a person, including all his genes - in the shape of DNA methylation, reveals a new study published in American journal Circulation: Cardiovascular Genetics. Some DNA methlyation sites have been found to remain even after 30 years of quitting smoking.
DNA methylation is a process by which cells control gene activity, and it often modifies the function of genes. Scientists have found that DNA methylation could reveal a person's smoking history, and as a result, they could develop targeted new therapies for diseases associated with smoking.
"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," says Dr. Stephanie J. London, last author of the Epidemiology Branch at the National Institute of Environmental Health Sciences.
"Equally important is our finding that even after someone stops smoking, we still see the effects of smoking on their DNA".
Research reveals that genes associated with smoking contribute to the increase and development of smoking-related diseases. Methylation is also a potential link between smoking and cancer, also as potential cause of development of chronic diseases in adults.
An estimated 40 million adults in the United States currently smoke cigarettes. Cigarette smoking is the leading cause of U.S preventable disease and death, accounting for more than 480,000 deaths every year. More than 16 million Americans live with a smoking-related disease.
Despite smoking rates declining in many countries worldwide as a result of smoking campaigns, even decades after people quit smoking, former smokers are at a long-term increased risk of diseases that include some cancers, chronic diseases, and stroke.
Researchers analyzed blood samples from almost 16,000 participants from 16 groups including a group from the Framingham Heart Study that researchers have followed-up since 1971.
Common methylation sites linked to cardiovascular diseases, cancers
In comparison with lifelong nonsmokers, the team found that DNA methylation sites associated with smoking were linked to more than 7,000 genes - accounting for one third of known human genes.
Findings suggest that the majority of DNA methylation sites in former smokers returned to levels observed in never smokers within 5 years of smoking cessation. However, some DNA methylation sites remained even 30 years after stopping smoking.
Investigators indicate that the long-term DNA methylation sites may emphasize genes that could put former smokers at risk of developing certain diseases years, even decades after quitting.
"The encouraging news is that once you stop smoking, the majority of DNA methylation signals return to never smoker levels after 5 years, which means your body is trying to heal itself of the harmful impacts of tobacco smoking,"