Objectives: The prevalence of cigarette smoking among Japanese men has been consistently high compared with males in Western countries over the past 30 years. However, during the same period, the incidence and mortality rates for lung cancer have been consistently lower in Japan than in Western countries, which has been termed the 'Japanese smoking paradox'. The odds ratio/relative risk of cigarette smoking for lung cancer mortality and incidence for the same number of cigarettes smoked per capita in Japan have been lower than those in Western countries. This difference in the odds ratio/relative risk is likely to be the main reason for the Japanese smoking paradox. The aim of this study was to clarify the reason for the difference in the odds ratio/relative risk between Japan and the USA.
Study design: Literature review to compare environmental, hereditary and other factors that may be related to lung cancer in Japan and the USA.
Results and conclusions: The main factors likely to have brought about the difference in the odds ratio/relative risk between Japan and the USA (and perhaps other Western countries as well) are: lower alcohol consumption by Japanese males; lower fat intake by Japanese males; higher efficiency of filters on Japanese cigarettes; lower levels of carcinogenic ingredients in Japanese cigarettes; and lung-cancer-resistant hereditary factors among Japanese males.