CHLORINATED
WATER CAN EFFECT CANCER RISK
Lifetime
consumption of chlorinated tap water can more than double the
risk of bladder and rectal cancers in certain individuals, two
new studies conclude.
Both studies examined
the lifetime water-consumption patterns, diets and lifestyles
of over 2,200 middle-aged and elderly Iowans suffering from either
bladder, colon, or rectal cancers. Those profiles were then compared
with those of a pool of nearly 2,000 healthy 'controls'.
Recent research has
suggested that chlorine reacts with naturally-found organic compounds
in water to form what the study authors call "chlorination
byproducts."
They say many of these
byproducts are "mutagenic and/or carcinogenic." The
first study found that smoking men who drank chlorinated tap water
for more than 40 years faced double the risk of bladder cancer
compared with smoking men who drank nonchlorinated water. Women
who drank chlorinated water, on the other hand, had only slightly
raised risks for bladder cancers, regardless of (their) smoking
status.
The second study found
that rates for rectal cancers for both sexes escalated with duration
of consumption of chlorinated water. Individuals on low-fiber
diets who also drank chlorinated water for over 40 years more
than doubled their risk for rectal cancer, compared with lifetime
drinkers of nonchlorinated water.
Similar differences
were also found between the risk patterns of chlorinated-water
drinkers who exercised at least once a week, and those who exercised
just once a month, or less. Experts have long recommended regular
exercise as one means of reducing one's risk of rectal and other
cancers.
The study found no
link between the long-term consumption of chlorinated tap water
and the incidence of colon cancer. This was not surprising, the
researchers explain, since colon tumors have very different patterns
of genesis and development compared with rectal tumors.
They speculate that
the source of chlorinated tap water may help determine its potential
to promote cancers.
Since surface water
(such as that found in lakes and reservoirs) usually contains
higher concentrations of organic compounds, the study authors
say it is also more likely to contain higher levels of (potentially
carcinogenic) chlorination byproducts, compared with water sourced
from deep underground.
Epidemiology 1998;9(1):21-28,
29-35
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