Drinking water and the prevalence of colorectal adenomas: an epidemiologic study in Telemark, Norway.

This study was based on an endoscopic screening study for detection of polyps in the rectum and sigmoid colon in a randomized, normal population sample of 400 individuals aged 50-59 years. Family disposition for cancer and indicators of lifestyle (including dietary registration) were recorded. The 310 individuals received domestic drinking water from one out of four public water supplies. The participants were categorized according to the water supply connected to their house of residence. Drinking water was analysed monthly during 2 years for chloroform, total organic carbon, colour index, calcium, magnesium and chlorine. The overall prevalence of colorectal polyps was significantly higher in residents receiving chlorinated water with a high organic content when compared with recipients of water with a low organic content. There was no association between polyp prevalence and chloroform concentration in the drinking water. Multivariate analysis revealed that age, male sex, high BMI, smoking, few stools per week, high protein intake and low intake of fibre, iron and cruciferous vegetables were far more important for the presence of polyps than the total organic content in chlorinated drinking water.