A research team in the U.S. coordinated by Dr. Stephanie London of the National Institute of Environmental Health Sciences reported Tuesday they found smoking also damages DNA. The study was published in the American Heart Association journal Circulation: Cardiovascular Genetics. After studying blood samples of 16,000 people taking part in various studies going back to 1971, researchers concluded that while most of the disease-causing genetic footprints left by smoking fade after five years if people quit, some appear to stay there forever. Practically, one-third of known human genes are affected. And heart disease and cancer are both caused by genetic damage. “The mechanisms for these long-term effects are not well understood. DNA methylation changes have been proposed as one possible explanation,” the study says. “We ended up finding a large signal, an order of magnitude more than any individual studies have seen.” Study author Dr Stephanie London said to media.