Damage to DNA from smoking fades over time but remains present for decades and possibly forever, according to a study reviewed in an American Heart Association journal and cited by NBC News.

Blood samples from 16,000 people given before and after they stopped smoking show most of the damage fades five years after quitting the habit. However damage in 19 genes lasted 30 years, and may be permanent, NBC said. Study authors include Roby Joehanes, of Hebrew SeniorLife and Harvard Medical School.