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Selenium May Cut Bladder Cancer Risk in Ex-Smokers

Mineral doesn't offer same protection to current, nonsmokers

FRIDAY, Nov. 1, 2002 (HealthDayNews) -- If you're a former smoker and want to protect yourself against bladder cancer, you might want to include selenium-rich foods in your diet.

A new study, published in the November issue of Cancer Epidemiology, Biomarkers and Prevention, found that ex-smokers who had high levels of selenium had a decreased risk of bladder cancer.

This effect didn't hold true for current smokers or non-smokers. The study authors suggest this is because non-smokers have not exposed their bodies to the same oxidative stress that former smokers have, and current smokers are overwhelming any positive effects from selenium due to the toxic chemicals found in tobacco.

Selenium is an essential trace mineral and antioxidant. It helps keep the immune system and the thyroid gland working properly. It is found in plant foods, meat, fish, cereal, dairy products, eggs and some nuts, particularly Brazil nuts. The selenium content of food varies, depending on how much selenium is present in the soil the food is grown in.

Selenium deficiency is unusual in the United States, but not so in other parts of the world. In places such as China and Russia, where the selenium content of the soil is low, selenium deficiency is more common. The recommended daily intake of selenium is around 55 micrograms. Doses higher than 400 micrograms daily could lead to side effects such as gastrointestinal problems, hair loss and mild nerve damage, according to the National Institutes of Health.

More than 50,000 Americans are diagnosed with bladder cancer every year, according to the National Cancer Institute. Worldwide, about 200,000 new cases occur annually, reports the study. Those at greatest risk for the disease include smokers, males, people over 40, whites and people who work with chemicals.

For the new study, researchers in the Netherlands studied data on more than 3,000 men and women who had participated in the larger Netherlands Cohort Study. The average age of the study volunteers was between 55 and 69 at the start of the study. Just over 400 of those studied developed bladder cancer during the six years of research.

All of the participants completed a questionnaire that helped the researchers assess and control for other possible cancer risk factors, such as alcohol use, diet, chemical exposure and a family history of bladder cancer. The volunteers also provided a toenail clipping, because analysis of toenail clippings gave the researchers an estimate of the average selenium intake during a year.

People who had at least 30 percent more selenium in their toenails had a slightly decreased risk of bladder cancer. However, the decrease in risk was greatest for ex-smokers. The researchers also found that higher selenium levels only seemed to affect invasive forms of bladder cancer.

None of the other known antioxidants, such as vitamin C, E and beta carotene, appeared to have any effect on bladder cancer rates in the study.

Commenting on the study, nutritionist Samantha Heller of New York University Medical Center says one possible reason smokers don't seem to get any benefit from selenium is that smoking might be depleting the mineral in their bodies.

She adds that if you want to prevent bladder and other cancers, supplementing with selenium isn't the answer.

"All of these healthy things work together as a team," Heller explains. So, if you supplement with selenium and a couple of other vitamins, you could still be missing out on essential nutrients. "It's like trying to play in the World Series without a pitcher or a third baseman," she adds.

The key, she says, is keeping everything in balance. That means stop smoking and start eating a balanced diet that includes lots of vegetables, nuts and legumes, Heller says.

The authors of the study conclude that more research needs to be done, and they don't recommend taking selenium supplements until more conclusive proof of its benefits is available.

What To Do

For more information on bladder cancer, visit the National Cancer Institute. To learn more about selenium, check with the National Institutes of Health or the University of Texas Health Science Center at Houston.

SOURCES: Samantha Heller, M.S., R.D., senior clinical nutritionist, New York University Medical Center, New York City; November 2002 Cancer Epidemiology, Biomarkers and Prevention
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