Background: Using a large-scale cohort of about 110,000 people established in 45 areas through-out Japan from 1988 through 1990, the study attempted to uncover the joint effects of combined smoking and alcohol intake on esophageal cancer mortality. Methods: A cohort established from 1988 through 1990 included 46,465 men and 64,327 women aged 40 years and older and younger than 80. The number of female smokers and drinkers was low, and women were excluded from the analysis for that reason. In addition, 308 people with histories of malignant neoplasm, and 3,579 with unclear smoking and drinking data were also excluded, resulting in 42,578 people available for analysis. A follow-up of these individuals was conducted until 1999. Cox proportional hazards model was used for the analysis. Results: The joint effects of number of cigarettes and amount of alcohol consumed per day were compared with non-smokers and non-drinkers or those consuming less than one unit of alcohol per day. An increased synergistic esophageal cancer mortality risk (3.88) for both smoking and drinking was observed for those smoking 20 cigarettes or less per day and drinking one unit of alcohol or more but less than three units per day, with the risk rising (6.30) for those smoking at least 21 cigarettes and drinking at least three units of alcohol per day. Even in non-smokers with increased alcohol consumption, and in non-drinkers or those drinking at most one drink per day with increased smoking, no increased risk was observed. Conclusions: In this cohort study of a Japanese population, increased esophageal cancer mortality risk was observed only when both factors of alcohol and tobacco intake were present simultaneously.
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