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.
