(Reuters Health) - People with moderately elevated levels of arsenic in their urine may have an increased risk of kidney cancer -- particularly if they have high blood pressure and kidney disease, a new study suggests.
The findings, reported in the Journal of Urology, do not prove that arsenic contributes to kidney cancer, however. One possibility, the researchers say, is that kidney cancer, by impairing the kidneys' ability to filter waste from the body, leads to increased arsenic levels in the urine.
Arsenic is an element found in rock, soil, water and air. It is also released into the environment through industrial activities, and can be found in products like paints, dyes and fertilizers.
High arsenic exposure can lead to cancer. And some studies -- but not all -- have linked even moderately elevated levels of arsenic in the body to high blood pressure and type 2 diabetes.
But in general, the potential health effects of chronic, low-level arsenic exposure remain unclear.
In the new study, researchers in Taiwan looked at the relationship between urinary arsenic levels and the risk of kidney cancer among people living in an area with low arsenic concentrations in the drinking water.
Most lived in Taipei City, where arsenic in tap water ranges from undetectable to 4 micrograms per liter.
In the U.S., the Environmental Protection Agency (EPA) has set an allowable limit of 10 micrograms per liter, and most U.S. drinking-water supplies have levels well below that.
The study researchers recruited 132 patients with kidney cancer and compared them with 260 cancer-free adults the same age.
Overall, there was an association between higher urinary arsenic levels and higher odds of kidney cancer, according to Dr. Yu-Mei Hsueh of Taipei Medical University and colleagues.
But the connection appeared strongest for people who had high blood pressure or impaired kidney function -- both established risk factors for kidney cancer.
If study participants had both of those conditions plus relatively high arsenic levels, their odds of kidney cancer were six times higher than those of people with none of the three risk factors.
Those with any two of those risk factors, meanwhile, had a four-fold increase in risk for kidney cancer.
In all, 17 kidney cancer patients and 17 cancer-free participants had all three risk factors.
It's possible, according to Hsueh's team, that arsenic exposure led to high blood pressure or kidney disease in some people, which then contributed to their kidney cancer.
That is a possibility, agreed Dr. Anthony Smith, chief of urology at the University of Mexico in Albuquerque, who was not involved in the study.
On the other hand, impaired kidney function might allow for greater concentrations of arsenic to build up in the urine.
"I don't think they really can tell from this study," Smith said in an interview.
He called the findings interesting, however, and said additional, larger studies to confirm or refute the results would be helpful.
"Arsenic exposure has been linked to a number of cancers -- bladder cancer, lung cancer, liver cancer," Smith noted. But it's unclear whether the low drinking-water exposures of people in the current study -- and most Americans -- present a cancer risk.
"Right now, they think this level is safe," Smith said, referring to the EPA threshold. "But no one knows for sure. It's still up in the air."
It is estimated that 13 million Americans live in areas where the public water supply exceeds the limit of 10 micrograms per liter. And unregulated private wells might also contain too much arsenic -- particularly in certain areas of the West, Midwest and New England where the groundwater contains high concentrations of the toxic chemical.
Experts suggest that people have private well water tested for arsenic. If the level exceeds 10 micrograms per liter, it can be treated with special filtration systems.
Worldwide, potentially dangerous arsenic levels in drinking water are major problem.
Researchers have estimated that about 140 million people around the world drink water with arsenic levels above 10 micrograms per liter. Bangladesh has been hardest hit, with millions being exposed to high levels of naturally occurring arsenic in well water.
SOURCE: bit.ly/kQoyKp Journal of Urology, June 2011.
By Amy Norton