Given the argument that “smoking causes lung cancer” it would be expected to logically follow that the incidence of lung cancer should mirror smoking prevalence. This is not, however, the case and has led to much discussion of “The Japanese Paradox”.
In Table 3 below we show for a selection of countries male smoking prevalence in 1960, 1970 and 1980 and 2008 data for the incidence of lung cancer among the total population, i.e. allowing a considerable period of time for the “incubation” of smoking-related harm. The contrast in lung cancer incidence in Japan despite much higher prevalence is marked.
There have been a number of academic attempts to justify this marked difference, with one study suggesting 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.
Each of these possible explanations may have merit, but it also suggests that there is a question of factors other than smoking which may have an influence on general health as well as incidence of cancers of any type. As the 2010 Marmot Review commented “A wide body of epidemiological and sociological evidence suggests that health inequalities are likely to persist between socioeconomic groups, even if lifestyle factors (such as smoking) are equalised”. Put more brusquely you are likely to live longer if you are well educated, live in a “nicer” area, have a good job, eat well and take exercise, with these latter factors almost inevitably linked to the previous ones. It is also the case, according to Cancer Research UK, that on a diagnosis of cancer those on higher incomes, with better jobs, etc, have a higher survival rate. Smoking is a major influence on health, but as each of these two reviews points out, it is not the only factor by any means.