Relation of cigarette smoking and alcohol use to colorectal adenomas by subsite: the self-defense forces health study.

While smoking has consistently been shown to be related to increased risk of colorectal adenomas, few studies have addressed the association between smoking and site-specific colorectal adenomas. The reported association between alcohol use and colorectal adenomas has been inconsistent. We evaluated risks of adenomas at the proximal colon, distal colon, and rectum in relation to cigarette smoking and alcohol use, and their interaction. Subjects were 754 cases with histologically proven colorectal adenomas and 1547 controls with normal colonoscopy among male officials of the Self-Defense Forces (SDF) undergoing total colonoscopy at two SDF hospitals. Statistical adjustment was made for hospital, rank, body mass index, physical activity, and either smoking or alcohol drinking. Cigarette smoking was significantly associated with an increased risk of adenomas, regardless of the location of the adenomas, but the increased risk associated with smoking was more pronounced for rectal adenomas. Alcohol use was associated with moderately increased risks of distal colon and rectal adenomas, but not of proximal colon adenomas. Cigarette smoking, but not alcohol drinking, was associated with greater increases in the risk of large adenomas and of multiple adenomas across the colorectum. There was no measurable interaction of cigarette smoking and alcohol drinking on colorectal adenomas. The findings corroborate an increased risk of colorectal adenomas associated with smoking and a weak association between alcohol use and colorectal adenomas. Further studies are needed to confirm whether smoking is more strongly related to rectal adenomas, large adenomas, or multiple adenomas.