The Japanese Lung Cancer Smoking Paradox

Relative Risk of Lung Cancer in Asia vs the United States

Asian man smoking, Japanese male smokers are less likely to get lung cancer
Why is lung cancer less common in Japanese men even though they smoke more?. Tdubphoto/Moment/Getty Images

Is it true that Japanese men smoke more but get lung cancer less frequently that men in the United States and Europe, even though they smoke more?  

This isn't a myth, It's true. But why?

The Japanese Lung Cancer Smoking Paradox

The seeming incongruity that those in Japan smoke more but have a lower lung cancer rate than the United States, is known as the “Japanese smoking lung cancer paradox.” The debate is not about smoking since we know that smoking causes lung cancer.

The debate is about why Japanese (and other Asian) smokers have a lower incidence of lung cancer, even though they smoke more. The answer to the questions surrounding this paradox is likely a combination of reasons.

Rates of Lung Cancer vs Smoking in Japan and the United States

Upon noting that there were more male smokers in Japan but a lower risk of lung cancer, researchers set out to make some comparisons. They found that the difference was not related to the amount of smoking. The men from the United States and those from Japan smoked for essentially the same number of years, and also averaged the same number of cigarettes daily.

Yet, while in the United States the "odds ratio" of lung cancer in male smokers vs non-smokers was 40.1 (in other words, male smokers were 40 times more likely to develop lung cancer than male non-smokers in the U.S.), the odds ratio in Japan was 6.3. In other words, male smokers in Japan were only 6.3 times as likely to develop lung cancer as male non-smokers.

 

Relative Rates of Lung Cancer in Other Asian Countries

The lung cancer paradox is clearly true, and is not isolated to Japan. The relative risk of lung cancer in an 2016 study found that, relative to the 40:1 relative risk in the United States, smokers in Korea were 4.0 to 4.6 times more likely to develop lung cancer than non-smokers.

The relative risk in Japan in this study was 3.7 to 5.1, and that in China was 2.4 to 6.5.

Authors of this study cautioned that the paradox should not be misinterpreted to mean that smoking is safer for Asians.

Probable Reasons for the Lung Cancer Smoking Paradox

Reasons that likely contribute to the higher risk of lung cancer in the United States vs some Asian countries include:

  • Lower levels of cancer-causing ingredients in Japanese cigarettes. In the United States, roughly 70 of the chemicals found in cigarettes are thought to cause cancer. While tobacco is present in most cigarettes, the type and proportion of these other chemicals can vary widely.
  • Genetic factors that result in Japanese men being more resistant to the smoking-related development of lung cancer. Though you may think of lung cancer as being a smoking-related disease, there are many causes, and some people carry a predisposition to the disease. This may be easier to understand if you have followed the stories about Angelina Jolie, and the decisions she faced upon learning she had a hereditary predisposition to breast cancer. In fact, one of these "breast cancer genes" known as BRCA2 is linked with a 2-fold risk of developing lung cancer in women who smoke.

    Possible Reasons for the Japanese Lung Cancer Smoking Paradox

    In addition to genetic tendencies and carcinogen content of cigarettes, there are other factors that may account for, or at least contribute to, the differences between smoking and lung cancer risk in the U.S. and Japan. These may include:

    • Lower alcohol consumption by Japanese males. High alcohol consumption is linked with a higher risk of lung cancer, though some types of alcoholic beverages may result in more risk than others. Genetic factors may also play a role in this factor, as one study found no link between alcohol and lung cancer in Chinese men.
    • Lower fat intake by Japanese males. A lower fat intake in the diet is associated with a lower risk of developing lung cancer.
    • The higher efficiency of filters in Japanese cigarettes. There is more use of activated charcoal in the filters of Japanese cigarettes than cigarettes available in the United States. You may be familiar with activated charcoal as it is used in emergency rooms to treat some poisonings and overdoses. Activated charcoal binds some chemicals, but certainly not all. In addition, activated charcoal is used in some health food supplements.
    • Earlier age of smoking onset in American men. American men begin smoking, on average, at least 2.5 years earlier than Japanese men. In general, lung cancer risk increases with the number of pack-years smoked, or the total number of cigarettes. But those who begin smoking at younger ages appear to be more at risk than those who begin smoking later, even if both groups were to smoke the same number of cigarettes.
    • Lifestyle factors other than smoking. Certain dietary factors are associated with a lower risk of lung cancer. In addition, exercise—even small amounts—appears to reduce the risk of lung cancer.

    What Can You Do With This Information?

    Certainly, genetic factors are beyond our control, but American men who smoke may wish to consider limiting their alcohol intake and consumption of high-fat foods.

    Make sure to check out these 10 tips for preventing lung cancer, whether or not you smoke. Keep in mind that lung cancer can, and does, occur in lifelong never smokers. Anyone with lungs can get lung cancer.

    Sources:

    Jung, K., Jeon, C., and S. Jee. The Effect of Smoking on Lung Cancer: Ethnic Differences and the Smoking Paradox. Epidemiology and Health. 2016. 38:e2016060.

    Marugame, T. et al. Lung cancer death rates by smoking status: comparison of the Three-Prefecture Cohort Study in Japan to the Cancer Prevention Study II in the USA. Cancer Science. 2005. 96(2):120-6.

    Nakaji, S. et al. Explanations for the smoking paradox in Japan. European Journal of Epidemiology. 2003. 18(5):381-3.

    Stellman, S. et al. Smoking and lung cancer risk in American and Japanese men: an international case-control study. Cancer Epidemiology Biomarkers and Prevention. 2001. 10(11):1193-9.

    Takahashi, I. et al. Differences in the influence of tobacco smoking on lung cancer between Japan and the USA: possible explanations for the ‘smoking paradox’ in Japan. Public Health. 2008. April 15 (Epub ahead of time).