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Researchers say people who have quit smoking have a lower risk of a number of cancers. Mattia/Stocksy
  • Stopping smoking reduces cancer risk at any age, especially after 10 years, according to a new study.
  • Researchers report that former smokers’ risks of developing lung cancer drop the fastest after stopping smoking.
  • Quitting when you’re younger has stronger benefits in cancer risk reduction, but the benefits of quitting after age 50 are still significant, the researchers said.

Quitting smoking at any age appears to significantly reduce a person’s risk of lung and other cancers.

That’s the conclusion of research published today in the journal JAMA Network Open.

For their study, researchers looked at a cohort of nearly 3 million people over the age of 30 with an average follow-up of 13 years.

In their findings, researchers reported that those who stopped smoking entirely had a 17% lower overall risk of cancer than those who continued to smoke. That included a 42% lower risk of lung cancer incidence, a 27% lower risk of liver cancer, a 14% lower risk of stomach cancer, and a 20% lower risk of colorectal cancer.

Of all cancers, lung cancer risks declined the most quickly following smoking cessation, falling three years earlier than other cancers. And while quitting before age 50 was better for improving your odds against a lung cancer diagnosis — averaging a 57% lower risk of lung cancer — even quitting after age 50 reduces lung cancer risk by 39% compared to continued smokers, the researchers reported.

“This is a very large population-based study that demonstrates that smoking cessation reduces cancer risk at any age, particularly at a younger age. It also provides insight into the importance of smoking cessation over a longer period and how this further reduces the risk of getting cancer,” said Dr. Anton Bilchik, a surgical oncologist, chief of medicine, and director of the Gastrointestinal and Hepatobiliary Program at Providence Saint John’s Cancer Institute in California.

“The limitations include that it is a retrospective population-based study and therefore does not have detail on non-cancer related deaths and the impact of smoking cessation,” Bilchik, who was not involved in the research, told Medical News Today.

One unusual finding was that the researchers found that cancer risk was slightly higher for 10 years post-quitting before falling to half the risk of those who continue to smoke after 15 years.

However, this can be explained by the data researchers were working with, according to Dr. Michael Siegel, a professor in the Department of Public Health and Community Medicine at Tufts University School of Medicine in Boston.

“The major limitation of the study is the inclusion of ‘sick smokers’ in the study, which means people who quit specifically because they already experienced cancer symptoms. This resulted in the observation of an increased risk of cancer for the first five years after smoking, which is an anomaly,” he told Medical News Today. “The sensitivity analysis showed that there is a steady decrease in cancer risk after smoking cessation. The main finding is that quitting smoking results in a substantial decrease in cancer risk within about five years, and by 10 years, the risk almost drops to that of nonsmokers.”

This aligns with a note from the study authors of a previous case-control study showing that past smokers who had quit for 10 years had nearly equal the liver cancer risks to those who had never smoked.

“These findings reinforce that it is never too late to quit smoking,” Siegel said. “There is never a time when it’s too late to start trying to quit. The health benefits of quitting occur almost immediately and even the cancer risks drop substantially in just a few years.”

Considering the health effects inclusive of, but not limited to, cancer risk is critical, experts say.

From the first hour to the first month to the first year of stopping smoking, people experience improvements in respiratory functioning and blood circulation and see their heart attack risk cut in half, among other benefits.

“This is the most important finding of this study,” Bilchik said. “No matter what age, don’t smoke, and if you do — stop! Also, do not assume that if you have been a long-term smoker, you have no hope. You do and this study supports it.”