Quitting Won’t Save You From Some Destructive Effects of Smoking

The largest study yet to explore the long-term effects of smoking on human DNA has revealed that cigarette addiction alters about 7,000 human genes, and some of the damage remains decades after quitting.

The study, published Tuesday in the American Heart Association's journal "Circulation: Cardiovascular Genetics," describes the impact of smoking on methylation, a mechanism that regulates gene expression.

Researchers examined the blood samples of 16,000 people and concluded that cigarette smoking permanently damages the human genome. Having analyzed methylation sites in regular smokers, and in those who had quit and in those who have never smoked a cigarette, they found that about one-third of known human genes are altered due to smoking.

Although the human body begins to heal as soon as smoking stops, some DNA methylation sites were shown to be damaged three decades later. Some of the 7,000 genes altered by cigarette use are known to aid in the development of diseases related to smoking, indicating that quitting is no guarantee of avoiding long-term tobacco-related illnesses, including lung cancer and heart disease.

"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," Roby Joehanes, first author and an instructor at Harvard Medical School in Boston, said in the study.

According to health experts, quitting significantly improves the chances of avoiding common tobacco-related illness, as most damage heals over time.

"The encouraging news is that once you stop smoking, the majority of DNA methylation signals return to never smoker levels after five years." Joehanes said.

According to the Centers for Disease Control and Prevention, nearly 40 million adults in America have smoked, or currently smoke cigarettes. Cigarette smoking, according to the CDC, accounts for one in every five deaths in the country annually.