About 45 million Americans are former smokers who, by quitting cigarettes, have dramatically cut their chances of getting heart disease, stroke and many cancers. But roughly a quarter will die from diseases caused by their old habit, experts say.
New science is helping explain why cigarettes' threat doesn't vanish. National Cancer Institute researchers have examined cells from the lungs and lung tumors of 28 smokers, 26 ex-smokers and 20 people who never smoked but still developed lung cancer. In both current and former smokers, more than 120 genes worked at far different rates than in the tissues of nonsmokers.
A surprisingly small number of smokes could harm your health for a surprisingly long time. Doctors have long noted lingering risks in people who in their lives smoked at least 100 cigarettes - just five packs. And while smokers who quit lower many cancer risks within five or 10 years, they remain at least twice as likely to die of cancers of the lung, mouth, voice box, esophagus and bladder as people who never lit up.
"When people stop smoking, their lung cancer risk tends to decrease over time," said Dr. Stephen Chui, an oncologist at the Cancer Institute of Oregon Health and Science University. "On the other hand, we've all had the experience of someone who smoked for a couple of years 25 years ago showing up with a horrible lung cancer."
Still, health experts are firm on one point: The fact that risk lingers long after the smoke from your last cigarette clears is no reason to keep smoking. While most smokers won't develop lung cancer, smoking is the main cause of lung cancer and the main preventable cause of death from all causes.
And quitting quickly makes you much less prone to many fatal problems.
Knowing that smoking may permanently alter genes in your lungs is a great reason not to start. So is knowing that even a few packs can hurt you permanently. Cigarettes aren't like alcohol, where a daily drink might help your health.
"Any amount of exposure to tobacco smoke is potentially bad," Chui said. "Every little bit adds to your risk. How many bullets do you want to put in that revolver before you spin it and put it to your head and pull the trigger?"
The message is especially important for kids. Young adults - people ages 18-24 - smoke more than people of other ages. And girls are among the fastest-growing group of smokers in the nation, even though lung cancer already kills far more women than breast cancer.