How smoking alters your DNA

Over 100 years ago, lung cancer was relatively uncommon. But this was well before Hollywood glamorized smoking and the tobacco industry launched mass advertising campaigns.

Today, lung cancer is the leading cause of cancer deaths, with approximately 125,000 expected deaths in the U.S., more than breast, prostate and colon cancers combined.

“It has been suggested since 1921 that smoking is implicated in lung cancer development,” Dr. Igor Medic, a Sharp Community Medical Group board-certified oncologist affiliated with Sharp Grossmont Hospital, says. “Fast forward to today, and the primary risk factor for developing lung cancer is cigarette smoking, which accounts for approximately 90% of all cases.”

Cigarette smoke and the DNA connection

Lung cancer occurs when cells in the lungs undergo changes in DNA caused by cigarette smoke. DNA, or deoxyribonucleic acid, is present in the cells of every living organism and carries genetic information necessary for development and functioning, including susceptibility to diseases like cancer.

Cigarette smoke contains over 7,000 chemicals, including carbon monoxide, hydrogen cyanide, ammonia, arsenic, formaldehyde and nicotine. Many are carcinogens — substances known to cause cancer.

When someone smokes, the chemicals enter the lungs and affect the entire body, including the DNA. Smoking causes lung cancer by damaging the cells that line the lungs. “Smoke directly damages genes inside normal lung tissue cells, transforming them into cancerous cells that grow and spread uncontrollably,” Dr. Medic says.

Initially, the body may be able to repair this damage. However, with repeated exposure, healthy lung cells are increasingly damaged and, over time, may develop into cancer.

Similarly, this is why secondhand smoke is so dangerous, and prolonged exposure is linked to a higher risk of lung cancer. “While the doses of carcinogens received from secondhand smoke exposure are far less than with active smoking, exposure can begin at birth and extend across the full lifespan, increasing risk,” Dr. Medic says.

Why some smokers develop lung cancer and others don’t

While we know that smoking increases a person’s risk of lung cancer, it’s less clear why only some smokers develop the disease. Studies suggest it may be genetic, and DNA repairs are more active in the genes of certain smokers, thus protecting them.

“All of us humans are made differently, with a different genetic makeup,” says Dr. Medic. “While some smokers have naturally more protective mechanisms to repair smoking damage, others do not.”

Quitting isn’t easy, but it’s worth it

Even if years of smoking have damaged your lungs, when asked if quitting is worthwhile, Dr. Medic always tells his patients, “Yes, it’s definitely worth quitting.”

According to the American Lung Association, after stopping for even:

• 20 minutes, your heart rate drops to a normal level

• 2 weeks to 3 months, your risk of a heart attack is lowered, and lung function improves

• 1 to 9 months, coughing and shortness of breath are reduced

• 1 year, your added risk of coronary heart disease is half that of a smoker's

The lowered risk for lung cancer becomes apparent within five years and continues to decline the longer you refrain from smoking. “Studies show that former ѕmоkers who had been abstinent for more than 15 years had an 80 to 90% reduction in risk of lung cancer compared with current smоkers,” Dr. Medic says.

He acknowledges that some lung damage remains, and risk remains higher than in individuals who never smoked, even after prolonged periods of complete smoking cessation. That said, he points to surveys that show adults who quit gained six to 10 years of life expectancy, depending on the age at which they quit.

When talking to his patients, Dr. Medic admits that stopping smoking is not easy. “We usually suggest a decrease in the amount you smoke, and then eventually, hopefully, fully quit,” he says.

He also says that all smokers should be offered therapy, including those who are ready to quit and those who are not. “It’s a combination of medication therapy and behavioral therapy, such as a smoking cessation clinic, which gives the best results.”

Talk with your doctor about your risk factors for lung cancer, advises Dr. Medic. You may meet the criteria for a noninvasive, low-dose CT scan, which is the best way to detect lung cancer early. It’s quick, painless and only takes about 20 minutes, he says.

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