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Both men and women who urinated at least twice at night were at 40% to 50% lower risk of developing bladder cancer, Dr Debra T. Silverman of the National Cancer Institute in Bethesda, Maryland, and her colleagues found.
The findings suggest, they say, that frequent urination may be protective because it reduces the amount of time the lining of the bladder is exposed to cancer-causing compounds in urine.
Research in animals and some small studies in humans have suggested that frequent urination may reduce bladder cancer risk, Silverman and her team note in the International Journal of Cancer.
How the research was done
To investigate the relationship on a larger scale, they compared 884 men and women who had recently been diagnosed with bladder cancer with 996 healthy "controls." The more a person urinated at night, the researchers found, the less likely he or she was to have bladder cancer. This effect was seen no matter how much water a person drank.
Smokers who didn't urinate at night were at seven-fold greater risk of bladder cancer than non-smokers, but smokers who did void during the night cut their risk in half.
Drinking water showed an independent effect on bladder cancer risk, with people who consumed at least 1.4 litres of water daily and who urinated at least twice nightly being at 80% lower risk compared to those who drank less than 0.4 litres daily and didn't urinate at night.
Night-time urination may be more protective because this is the period when people typically go the longest without voiding, the researchers say.
"If confirmed, innovative approaches will be needed to translate this finding into meaningful prevention of the occurrence of the nearly 357 000 bladder cancer patients newly diagnosed worldwide annually and the 145 000 deaths," they conclude. – (Reuters Health, October 2008)
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