Fluid intake and risk of bladder and other cancers.

There are appreciable differences in total fluid intake at the individual and population level, and substantial difficulties in obtaining valid measures of fluid intake. Epidemiological studies have examined the association between fluid intake and different types of cancer. For bladder cancer, fluid consumption has been associated with a moderate increase of risk in some studies, including a multicentric case-control study from the United States, based on about 3000 cases, with a decrease in others, including the Health Professional Follow-up study, or with no material association. The evidence, therefore, is far from consistent. Sources and components of fluids were also different across different types studies. From a biological point of view, a decreased fluid intake could result in a greater concentration of carcinogens in the urine or in a prolonged time of contact with the bladder mucosa because of less frequent micturition. Carcinogenic or anticarcinogenic components of various beverages excreted in the urine may also play a role in the process. It has been suggested that fluid consumption has a favorable effect on colorectal cancer risk. Fluid intake may reduce colon cancer risk by decreasing bowel transit time and reducing mucosal contact with carcinogens. Low fluid intake may also compromise cellular concentration, affect enzyme activity in metabolic regulation, and inhibit carcinogen removal. However, epidemiological data are inadequate for evaluation. Data are sparse and inconsistent for other neoplasms, including breast cancer. The fluid constituent of foods, confounding, interactions and possible influences of specific types of beverages should be investigated further. In conclusion therefore the association between total fluid intake and cancer risk remains still open to debate.