Tap water may raise bladder cancer risk: study

Reuters Health
May. 06, 2006

NEW YORK (Reuters Health) - Pooled data from six case-control studies suggest that higher consumption of tap water-based drinks may slightly increase the risk of bladder cancer among men.

The increased risk of bladder cancer with tap water consumption was "consistently found in all six studies, making chance an unlikely explanation," write investigators in the International Journal of Cancer.

They caution, however, that for now, the study finding that tap water "is associated with a slight increased risk of bladder cancer" does not readily translate into public health recommendations.

The results are based on 2,749 bladder cancer cases and 5,150 cancer-free controls. Most of the subjects resided in the US, Canada or Finland, with data from subjects in France and Italy also included.

The investigators observed that the risk of bladder cancer was 50 percent higher in men who drank more than 2.0 liters of tap water per day compared with those who drank 0.5 liters or less of tap water per day. Results among women were less consistent.

Coffee made up, on average, about one third of the tap water intake and heavy coffee consumption, defined as more than 5 cups per day, increased bladder cancer risk, especially among men who smoked.

However, consumption of tap water excluding coffee was also associated with an increased risk of bladder cancer.

Drinking fluids other than tap water was not associated with bladder cancer risk, reports the study team led by Dr. Christina M. Villanueva from Institut Municipal d'Investigacio Medica in Barcelona, Spain.

The association between bladder cancer and tap water consumption, but not with non-tap water fluids, suggest to investigators that the increased risk may be related to the cancer-causing contaminants in tap water, such as disinfection by-products.

Disinfection by-products are chemicals generated through reactions of disinfectants (such as chlorine) with organic matter naturally occurring in water. Trihalomethanes are usually the most prevalent by-products of chlorination.

However, in the current study, the increased risk of bladder cancer among those who drink large amounts of tap water was independent of trihalomethane exposure.

SOURCE: International Journal of Cancer, April 15, 2006.