[Total fluid intake, urination frequency and risk of bladder cancer: a population-based case-control study in urban...

To evaluate the association between total fluid intake and the time of urination per day and the risk of bladder cancer.

A population-based case-control study was conducted in urban Shanghai, China, during January 1996 to December 1998. The study included 608 incident cases of bladder cancer and 607 age- and sex-matched controls. Unconditional logistic regression models were used to estimate the odds ratios (ORs) and their corresponding 95% confidence intervals (95%CIs) for bladder cancer associated with frequency of urination, after adjusted for age, gender, smoking status, history of occupation with high risk, history of bladder infections, body mass index and other confounding factors. The level of statistical significance was set at 0.05 (two-sided).

No significant trend was observed for the association between total fluid intake, time of nighttime urination and the risk of bladder cancer. Increasing time of urination during daytime was associated with decreased risk of bladder cancer (P for trend = 0.014). ORs (95%CIs) for subjects who voided 4 times, 5 times and 6 or more times per day [0.72 (0.49 - 1.05), 0.60 (0.41 - 0.87) and 0.62 (0.43 - 0.90), respectively], when compared with those with less than 4 times per day after adjustment of confounding factors. Data showed that smokers and nonsmokers who voided at least 6 times per day had the ORs of 0.72 (95%CI: 0.45 - 1.15) and 0.46 (95%CI: 0.25 - 0.87) when compared to their counterparts who voided 3 times or less per day during the daytime. Subjects who urinated at least 6 times per day and consumed more than 1500 ml of total fluid per day experienced a significant 57% reduction in risk compared to subjects who urinated 3 times or less and consumed less than 750 ml of total daily fluid intake.

Increased urination frequency and total fluid intake, especially among those who never smoked might be associated with a reduced risk of bladder cancer.