Drink a Toast to Tap Water
Study Suggests Water Consumption Benefit Outweighs THM
Many water treatment systems use chlorine to disinfect drinking
water. However, chlorine reacts with dissolved organic matter in water
to create trihalomethanes (THMs), which have been associated with
excess risk of bladder cancer in people who drink chlorinated water.
Now, in a large study conducted in Spain, an international team of
scientists has examined the role of tap water and total fluid intake in
bladder cancer risk, while also assessing the effect of exposure to
THMs in water
[
EHP 115:1569–1572; Michaud et al.].
The results suggest that higher water consumption is associated with
lower risk of bladder cancer, regardless of THM exposure.
Some studies have linked high consumption of fluids including tap
water with a lower risk of bladder cancer, perhaps because urinating
more frequently allows more flushing of the bladder. Other studies
suggest that high tap water consumption could increase bladder cancer
risk if chlorination by-products or other water contaminants such as
arsenic are elevated in the water source. Adding to this complexity is
that still other studies have shown a THM-related excess risk of
bladder cancer in men but not women.
Between June 1998 and June 2001, researchers
conducted a hospital-based case–control study of bladder cancer in
multiple centers in Spain. Male and female bladder cancer patients aged
20–80 years were recruited from 18 participating hospitals. For the 397
bladder cancer cases available for this analysis, the team recruited
664 matched controls who had been admitted to the same hospitals around
the same time for hernias, fractures, orthopedic problems, and other
reasons.
Trained interviewers collected information during
each subject's hospitalization that included sociodemographic
characteristics, family history of cancer, smoking history,
occupational history, residential history, drinking water source at
each residence, beverage consumption (including water), and medical
history. The researchers used local government and water company data
on annual average THM levels, water source history since 1920, and
chlorination history to calculate average year-by-year THM exposure.
These data were available for 78.5% of the total study person-years.
The researchers examined the association between
total fluid and water consumption and bladder cancer risk, while also
examining the interaction between water intake and THM exposure. The
results suggest that drinking more water, even from chlorinated sources
with high THM levels, is beneficial in reducing risk of bladder cancer.
The authors found a 53% lower risk of bladder cancer in people who
drank 1,400 mL or more water per day compared with those who drank less
than 400 mL per day after adjusting for known and potential
confounders. This inverse association held across all strata of smoking
status and THM exposure, and for both men and women.
The study was strengthened by high response rates
from cases and controls, detailed interview data on individual beverage
consumption, detailed assessment of THM exposure, and detailed data on
smoking, which is believed to be the greatest risk factor for bladder
cancer.
Originally published on http://www.ehponline.org
