Smoking Duration vs. Intensity and the Impact on Lung Cancer Risk

Reading time: 6 – 9 minutes

We’ve discussed smoking and health a number of times recently:

One of our readers asked a question I’m sure many have us have wondered about at one time or another:
Smoking tightrope
Which is worse for the development of lung cancer — smoking heavily over a short period of time or smoking fewer cigarettes over many years?

Here’s what the research has to say:

In 2003, researchers at Memorial Sloan-Kettering Cancer Center created a prediction tool that can assess a long-term smoker’s absolute risk of developing lung cancer within 10 years. How long and how much people have smoked, as well as how long it’s been since their last puff, affect the risk of getting lung cancer.

The formula for the study was published in the Journal of the National Cancer Institute. I’ve linked to the full article since it’s publicly available. The study uses a number of predictors, including age, duration of smoking, average amount smoked per day while smoking and duration of abstinence from smoking (for former smokers) [1]. These predictors are not only identifiable from a clinical history but they are established or strongly suspected risk factors for lung cancer. Additionally, they are also risk factors for all-cause mortality.

Figure 1 models multivariable relations between 1-year lung cancer risk and (A) duration of smoking, (B) average number of cigarettes smoked per day, (C) duration of abstinence and (D) age. In panel A, the relative risk of lung cancer increases exponentially with duration of smoking. In contrast, panel B shows that the relative risk of lung cancer tends to level off between 30 and 60 cigarettes smoked per day.

What does this mean? It means that the relative risk of tobacco-attributable lung cancer sharply increases with increasing duration of smoking, much more so than smoking intensity (i.e. the number of cigarettes smoked per day).

The model for the prediction tool was derived from data collected during CARET, a multicenter, randomized, controlled study that evaluated the impact of beta-carotene and vitamin A supplementation on lung cancer incidence and mortality [2]. Unfortunately, the prediction tool only works for people age 50 and older who smoked at least 10 cigarettes a day for at least 25 years, since those were the people tracked for cancer development in the study.

Further research found that the model described above slightly underestimated the observed risk of lung cancer over 10 years [3]. I choose to write about this particular study because of the accessibility of the online prediction tool. However, other risk models have been developed [4-6].

Additional studies have also suggested that smoking duration has a stronger effect in the prediction of lung cancer risk than number of cigarettes smoked per day [7-10]. These models are consistent with the results from epidemiologic studies, which indicate that risks of lung cancer, as well as bladder cancer, tend to level off with increased smoking intensity [11].

Smoking cessation at any age is beneficial. Nevertheless, lower lung cancer death risk is observed for people who quit at younger ages [12]. Indeed, cessation of smoking prior to middle age is associated with a more than 90% reduction in cancer risk attributed to tobacco [13].

This isn’t to say that smoking intensity isn’t a major contributor to tobacco-attributable cancer risk. However, the take-home message is that long-term smoking clearly impacts lung cancer risk to a greater extent. That’s why it’s more important than ever to quit smoking now.

References

  1. Bach et al. Variations in lung cancer risk among smokers. J Natl Cancer Inst. 2003 Mar 19;95(6):470-8.
    View abstract
  2. Omenn et al. The beta-carotene and retinol efficacy trial (CARET) for chemoprevention of lung cancer in high risk populations: smokers and asbestos-exposed workers. Cancer Res. 1994 Apr 1;54(7 Suppl):2038s-2043s.
    View abstract
  3. Cronin et al. Validation of a model of lung cancer risk prediction among smokers. J Natl Cancer Inst. 2006 May 3;98(9):637-40.
    View abstract
  4. Peto et al. Smoking, smoking cessation, and lung cancer in the UK since 1950: combination of national statistics with two case-control studies. BMJ. 2000 Aug 5;321(7257):323-9.
    View abstract
  5. Prindiville et al. Sputum cytological atypia as a predictor of incident lung cancer in a cohort of heavy smokers with airflow obstruction. Cancer Epidemiol Biomarkers Prev. 2003 Oct;12:987-93.
    View abstract
  6. Cassidy et al. Defining high-risk individuals in a population-based molecular-epidemiological study of lung cancer. Int J Oncol. 2006 May;28(5):1295-301.
    View abstract
  7. Doll and Peto. Cigarette smoking and bronchial carcinoma: dose and time relationships among regular smokers and lifelong non-smokers. J Epidemiol Community Health. 1978 Dec;32(4):303-13.
    View abstract
  8. Peto, R Influence of dose and duration of smoking on lung cancer rates. Zaridze, D Peto, R eds. Tobacco: a major international health hazard; proceedings of an international meeting Moscow, USSR, June 4-6, 1985. 1986 World Health Organization, International Agency for Research on Cancer Lyon, France. International Agency for Research on Cancer Science Publication No. 74, 23-33.
  9. Flanders et al. Lung cancer mortality in relation to age, duration of smoking, and daily cigarette consumption: results from Cancer Prevention Study II. Cancer Res. 2003 Oct 1;63(19):6556-62.
    View abstract
  10. Lubin and Caporaso. Cigarette smoking and lung cancer: modeling total exposure and intensity. Cancer Epidemiol Biomarkers Prev. 2006 Mar;15(3):517-23.
    View abstract
  11. Vineis et al. Levelling-off of the risk of lung and bladder cancer in heavy smokers: an analysis based on multicentric case-control studies and a metabolic interpretation. Mutat Res. 2000 Jul;463(1):103-10.
    View abstract
  12. Halpern et al. Patterns of absolute risk of lung cancer mortality in former smokers. J Natl Cancer Inst. 1993 Mar 17;85(6):457-64.
    View abstract
  13. Peto et al. Smoking, smoking cessation, and lung cancer in the UK since 1950: combination of national statistics with two case-control studies. BMJ. 2000;321:323-329.
    View abstract
About the Author

Walter Jessen is a senior writer for Highlight HEALTH Media.

Comments

  1. Interesting. No one talks about the intensity of smoking vs long term use. The message is clear, quit and quit fast.

  2. Thanks for answering my question.

    So, basically, once you smoke around 30 cigarettes per day, you’re already doing more or less the maximum amount of damage and so smoking more than this makes little difference?

    This is good news for me, since I smoked extremely heavily throughout my college years, very lightly (i.e. one pack every few weeks) for about 5 years after that and not at all for over a year now (since age 30).

    I think I am quite lucky in that I haven’t experienced any of the adverse effects associated with stopping smoking (other people I know aren’t so fortunate), and I can certainly use the extra money.

    I have no plans to resume!

  3. I wouldn’t say you’re doing the maximum amount of damage smoking 30 cigarettes per day – clearly someone smoking more than that would be doing further damage to their lungs. However, from a relative risk standpoint, the risk of being diagnosed with lung cancer increases at a higher rate from 1 to 30 cigarettes than from 30 up. Don’t forget that smoking is associated with a higher risk for the development of other diseases, including other types of cancer and cardiovascular and respiratory diseases.

    I think Chrysalis summed it up nicely – quit and quit fast.

  4. Interesting study.
    Having been a smoker for more years than I would care to admit, I decided that enough is enough and have been smoke free for the last 6 months with no withdrawal symptoms – fortunately.
    The reason for this might have been that I never smoked in our house, car or anybody else’s house or car nor did I choose to sit in the smoking section of restaurants, etc.
    I recently went in and had an ultrasound scan of all major arteries, and organs and, to the tech’s amazement, there was not plaque or other obstructions to any part of my body. I also underwent a breathing examination and was quite surprised to find that my lungs are 80% clear – and was told with more exercise my lungs would attain 90%+ within a year.
    Thanks for the article. Most interesting and congratulations to all of you who have chosen to live longer by their deciding to be smoke free.

  5. Hi Morgan – congratulations on being smoke free! It sounds like you had your addiction somewhat under control even before you quit. I’m glad to hear the damage to your arteries and lungs is minimal. Isn’t it interesting how smoking injury differs from person to person? A number of genes are thought to contribute to the susceptibility to tobacco smoke toxicity, including enzymes involved in the metabolism of xenobiotics.

    Palma et al. Influence of glutathione S-transferase polymorphisms on genotoxic effects induced by tobacco smoke. Mutat Res. 2007 Sep 1;633(1):1-12. Epub 2007 Jun 2.
    View abstract

  6. I love to hear the stories of people quitting. It was too late for my father he smoked from 13 till he was 45. He passed away because of smoking. I can’t believe its not against the law.

  7. Very Interesting. This, I guess, is also some good news for my ears, since I have recently quit smoking. To all of you who read this article, just quit smoking. The information above should be motivation in and of itself. The first three days being smoke free are the worst and once you get past the first three months smoke free you are free and clear.

  8. Now there is a rather pointless study. It assumes cancer is your biggest worry. In fact heart attack, stroke, emphysema, and chemical imbalances will do it’s toll as you accumulate the solid poisons, no matter how slow or fast you do it. The emphasis should be on 1)techniques for quitting 2) educational material that prevents starting in the first place.

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