A study published in the journal Circulation: Cardiovascular Genetics shows that smoking actually leaves a “footprint” on our genome in the form of DNA methylation, which has been linked with cancer and other health problems. Apparently, DNA methylation goes back to normal after some people stop smoking, while for others, it lasts even after 30 years of quitting.

The study relates smoking-associated DNA methylation with over 7,000 genes or one-third of our genes. The methylation sites were linked to gene disruptions that are associated with cardiovascular diseases, pulmonary diseases, certain cancers and other illnesses caused by smoking.

Although the study was not intended to examine the effects of the habit over long periods of time, this one is the biggest study to investigate its consequences on DNA methylation.

The study involved a meta-analysis of DNA methylation sites across the human genome using blood samples of 16,000 individuals composed of smokers, non-smokers and former smokers of the Cohorts for Heart and Aging Research in Genetic Epidemiology (CHARGE) Consortium as well as from the Framingham Heart Study.

The findings also reveal that we can still see DNA changes caused by the habit even years after the person quit. This indicates that DNA methylation can reveal signs or biomarkers that tell us of a person’s history, which could pave the way for new and improved treatments that target these methylation sites.

“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,” points out the study’s first author Roby Joehanes Ph.D. of Hebrew SeniorLife, and an instructor at Harvard Medical School in Boston, Massachusetts. “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.”