Water intake may be associated with a slightly reduced risk of bladder cancer, especially in women, a study suggests.

The study, conducted in Los Angeles County, involved 1,586 bladder cancer patients and an equal number of age-, sex-, and race-matched neighborhood controls. Investigators led by Xuejuan Jiang, PhD, of the University of Southern California in Los Angeles, obtained information on total fluid intake from the consumption of specific fluids, such as water, coffee, tea, alcohol, milk, juice, hot chocolate, and soda.

Total fluid intake was not associated with bladder cancer, but daily water intake was. Compared with drinking less than one glass of water daily, drinking six or more glasses daily resulted in a 31% decreased risk of bladder cancer in women and a 6% decreased risk in men, investigators reported in the International Journal of Cancer (2008;123:1649-1656).

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Daytime urination frequency modified the association. Among men and women who urinated at least six times daily, drinking six or more glasses of water per day was associated with a significant 59% decreased risk of bladder cancer compared with drinking less than one glass per day.

The researchers wrote that their results are consistent with a hypothesis first proposed in 1974, “which attributes development of bladder cancer to prolonged exposure to carcinogens in urine. A high intake of water can dilute the urine, increase the frequency of urination, and thereby reduce the contact of carcinogens with the urothelium.”

In a separate study published in the same issue (pp.1644-1648), investigators found a link between nocturia and a lower risk of bladder cancer. Voiding at least two times per night was associated with a significant 40%-50% reduced risk. Nocturia reduced the risk associated with cigarette smoking.

The authors wrote that their findings “provide evidence in humans that bladder cancer risk is related to the contact time of the urothelium with carcinogens in urine.”