Fluid intake and risk of bladder cancer in the Nurses' Health Studies.

Increase in fluid intake may reduce bladder cancer risk by decreasing the contact time between carcinogens in urine and bladder epithelium. However, this association has not been examined in a large cohort of women. The association between total fluid intake and bladder cancer risk in two large prospective women's cohorts with 427 incident bladder cancer cases was examined. Detailed information on total fluid intake was collected by repeated food frequency questionnaires over time. Multivariable relative risks (RRs) and 95% confidence intervals (95% CIs) were estimated by using Cox proportional hazards regression models. Results from the two cohorts were pooled together using the random-effects model. Using the average values from the earliest two dietary assessments and lowest quartile as reference, a suggestive inverse association was observed between total fluid intake and overall bladder cancer risk (RR: 0.83, 95% CI: 0.61-1.12, p-value for trend: 0.08), and invasive bladder cancer risk (RR: 0.47, 95% CI: 0.23-0.97, p-value for trend: 0.04). Among heavy cigarette smokers, women with the highest quartile of total fluid intake had a 38% decrease in bladder cancer risk (RR: 0.62, 95% CI: 0.41-0.93, p-value for trend: 0.02). The findings suggested that total fluid intake may reduce bladder cancer risk for female smokers, as well as reduce the risk of invasive bladder cancer.