Smoking reduction, and especially smoking cessation, were shown to be associated with lowering cancer risks in a population-based study. Results of the study were published in the journal Cancer.

The study was based on records from the National Health Insurance Service in South Korea, which serves 97% of the nation’s population. It included information from current smokers aged 40 and older who participated in consecutive biennial health examinations in 2009 and 2011. Participants were followed from 1 year after the last screening until December 31, 2018. Persons with certain health conditions or incomplete information were excluded from analysis.

The study analyzed smoking behavior based on responses to a self-administered questionnaire. Participants were categorized according to daily smoking-related behaviors at each health examination. In 2009, those participants who smoked were categorized as light smokers (fewer than 10 cigarettes), moderate smokers (10 to 19 cigarettes per day), and heavy smokers (20 or more cigarettes per day).

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Based on responses to the questionnaire at the 2011 examination, those participants were categorized as quitters (stopped smoking between the 2 examinations), reducers I (reduced smoking by 50% or more without quitting), reducers II (reduced smoking by 20% to 50% without quitting), sustainers (smoking habits varied by less than 20%), and increasers (an increase of 20% or more). The study endpoint was newly diagnosed cancer, excluding thyroid cancer.

A total of 893,582 participants were included in the analysis. Between 2009 and 2011, 20.6% of participants had quit smoking; 7.3% were categorized as reducers I, 11.6% as reducers II, 45.7% as sustainers, and 14.8% as increasers.

Using sustainers as the reference group, participants who quit smoking experienced the lowest risk of cancers overall (adjusted hazard ratio [aHR], 0.94; 95% CI, 0.92-0.96), as well as the lowest risks of smoking-related cancers (aHR, 0.91; 95% CI, 0.89-0.93) and lung cancer (aHR, 0.79; 95% CI, 0.76-0.83).

Participants in the reducers I category also reportedly showed decreased risks of cancers overall (aHR, 0.96; 95% CI, 0.93-0.99), smoking-related cancers (aHR, 0.95; 95% CI, 0.92-0.99), and lung cancer (aHR, 0.83; 95% CI, 0.77-0.88), relative to sustainers. Participants in the reducers II category also showed reductions in risks compared with sustainers.

A third screening with 682,996 of the participants was conducted in 2013. When evaluating results from the 3 consecutive screenings, participants who shifted from the category of reducer II to reducer I showed a greater reduction in risk of lung cancer (aHR, 0.74; 95% CI, 0.58-0.94), relative to sustainers. Participants who shifted from reducer I to quitter category showed decreased risks in smoking-related cancers (aHR, 0.81; 95% CI, 0.71-0.92) and lung cancer (aHR, 0.66; 95% CI, 0.52-0.84), relative to those who maintained their status as reducer I. Participants who resumed smoking after quitting showed increased risks of smoking-related cancers (aHR, 1.19; 95% CI, 1.06-1.33) and lung cancer (aHR, 1.48; 95% CI, 1.21-1.80), relative to participants who continued to abstain from smoking.

“These findings suggest that although smoking reduction has substantial benefit for cancer prevention, especially for those who cannot quit, smoking cessation should be encouraged whenever possible, and quitters should be carefully monitored to ensure that they do not resume smoking,” the investigators concluded.


Yoo JE, Han K, Shin DW, et al. Effect of smoking reduction, cessation, and resumption on cancer risk: a nationwide cohort study. Cancer. Published online March 17, 2022. doi:10.1002/cncr.34172