Alcohol drinking and lung cancer risk: An evaluation based on a systematic review of epidemiologic evidence among the Japanese population

Background: The relationship between alcohol consumption and risk of lung cancer is controversial. Based on a systematic review of epidemiologic evidence, we evaluated this association among the Japanese population, who may be more susceptible to alcohol-related diseases than Western populations. Methods: Original data were obtained from MEDLINE searches using PubMed or from searches of the Ichushi database, complemented with manual searches. The evaluation of associations was based on the strength of evidence and the magnitude of association, together with biological plausibility as previously evaluated by the International Agency for Research on Cancer. Results: We identified seven cohort studies and twocase-control studies. One cohort study demonstrated a strong positive association between alcohol drinking and the risk of female lung cancer, but the association almost disappeared after adjustment for smoking. The other eight studies showed a weak positive or no association. Although smoking is the best-established risk factor for lung cancer, only five cohort studies presented smoking-adjusted risks out of all nine identified. Furthermore, only two studies explicitly reported the risk estimate for ex-drinkers who may have quit alcohol drinking after the development or diagnosis of the disease and have an apparently higher risk. Conclusion: We conclude that the epidemiologic evidence on the association between alcohol drinking and lung cancer risk remains insufficient in terms of both the number and methodological quality of studies among the Japanese population.