[Association of drinking water source and colorectal cancer incidence: a prospect cohort study]

The pollution of drinking water, for example river and pool, has long been recognized to be associated with an increased risk of colorectal cancer (CRC) in previous epidemiological studies. There is little prospect cohort study with person-years directly on the relative risks of different sources of drinking water for CRC.

From May 1989 to April 1990, a screening for CRC was carried out among residents aged 30 and over 30 years in 10 villages and towns of Jiashan in China. A total of 64115 residents who participated the screening were classified into 5 cohorts by the source of drinking water and were followed-up for CRC incidence through a tumor reporting system including a rapid reporting system of CRC Registry and for death instance through Death Registration of Jiashan. After 11 years of follow-up, person-years calculated with every cohort member, the incidence densities of CRC with different sources of drinking water were analyzed respectively. Poisson regression was used to control potential confounding variables including demography variables and smoke history and to attain crude and adjusted relative risks based on person-years.

A trend was seen toward increasing incidence rates of colorectal cancer from municipal, river, channel, mixed water to well source in turn as shown as 29.61, 32.67, 33.45, 40.87, 58.67 per 100,000 inhabitants, and only the role in risk of well water was marked different from municipal water (P< 0.05). After adjusted the confounding variables by multi-Poisson regression, we found the significant risk of drinking well water for colon cancer, rectal cancer, and colorectal cancer. The relative risks were 1.741 (95%CI 1.001-3.029), 2.228 (95%CI 1.432-3.466), and 2.022 (95%CI 1.432-2.854), respectively.

Drinking well water long is a risk factor for colorectal cancer in Jiashan, especially for rectal cancer.