Preventing Prostate Cancer So Far, No Clear Answers

Nutrition Action Healthletter, July, 2001 by Bonnie Liebman

The odds aren't good.

One out of six American men will be diagnosed with prostate cancer over the course his lifetime. Every year, the disease kills 31,500 men.

But prostate cancer isn't a universal death threat. For years, researchers have been trying to figure out why the U.S. mortality rate is ten times higher than it is in countries like China. They're still trying.

Now, for the first time, the evidence is strong enough that the National Cancer Institute (NCI) is set to launch a ten-year trial on 32,000 men to see if two supplements--selenium and vitamin E--can cut the incidence of prostate cancer.

"If this study shows a reduction in cancer rates anywhere near what we've seen in earlier trails, it would put a dent in the 200,000 new cases of prostate cancer we see annually," says NCI researcher Demetrius Albanes. But some experts worry that the trial is testing the wrong kind of selenium and vitamin E. "We have to keep our fingers crossed and hope for positive results," says Tim Byers, a professor of preventive medicine at the University of Colorado in Denver. "We could use some.

The death count alone--31,500 lives lost every year--doesn't begin to measure the anxiety, misery, and pain caused by prostate cancer. Yet after years of research, experts don't have many answers for men who want to dodge the disease through diet.

"When you put all the data together, it looks like diet is definitely important," says Edward Giovannucci of the Harvard School of Public Health. "But we can't make any firm recommendations yet."

That's little comfort to men who've seen friends or family members die of the disease or who have a high risk themselves. "So far, we have nothing definite to help men who have a PSA of 8 and have to get a biopsy every six months," says Peter Gann of the Northwestern University Medical School in Chicago. (Doctors use blood levels of PSA, or prostate specific antigen, to screen men for early prostate cancer.)

Nor do researchers have anything definite to help men who face impotence, incontinence, or other side effects from the treatment of prostate cancer. And then there are the men who have succumbed to the disease. Larry Clark was the University of Arizona researcher whose 1996 study found such a remarkable drop in prostate cancer rates that it led the National Cancer Institute (NCI) to mount its new selenium trial. In March 2000, Clark died--of prostate cancer--at the age of 51.

Here's what scientists know so far about diet and the cancer that strikes more American men than any other.

SELENIUM

In the 1980s, when Larry Clark and colleagues assigned 1,300 people to take either 200 micrograms of selenium or a placebo every day, no one suspected that selenium might prevent prostate cancer. Their goal was to see whether it could prevent skin cancer in residents of the Southeast, where the soil and people's diets--are selenium-poor.(1)

"Selenium supplements had no effect on the recurrence of skin cancer," Clark told Nutrition Action Healthletter in 1996. "But the three leading cancers--lung, prostate and colon--all decreased."

Decreased by an unheard-of two-thirds, that is. The researchers had to stop the study three years early because the selenium-takers fared so much better that it would have been unethical to keep people on the placebo.

Still, Clark was cautious about his findings. "Selenium is not going to help everybody, and it's not going to cure all cancer," he explained.

It's possible that selenium only works in people who get too little from their food ... or that Clark's results were a fluke.

But worth another trial? You bet.

The National Cancer Institute (NCI) doesn't expect results from its new trial, called SELECT, for about a decade (see "SELECT One Option," p. 5). Meanwhile, some researchers are worried that SELECT may not be using the right kind of selenium supplement.

Clark's trial used a high-selenium yeast. (SelenoExcell is the brand that is closest to the supplement Clark used--see "The Bottom Line," p. 5.) SELECT will use selenomethionine, which is the most abundant form of selenium found in the yeast. An expert panel recommended selenomethionine instead of yeast because selenium and other constituents of the yeast vary too much from batch to batch, explains the NCI's Demetrius Albanes.

Let's hope it was the right choice.

"I'm concerned that there might be some bioactive compounds in the yeast that aren't in the selenomethionine supplements," says Colorado's Tim Byers, who served on a safety committee for the 1996 study. "If the new study fails, we won't know why."

VITAMIN E

Like selenium, vitamin E's link with the prostate showed up in a clinical trial designed to test something else.

The Alpha-Tocopherol Beta-Carotene (ATBC) study tested a daily dose of 50 International Units (IU) of vitamin E (that's the alpha-tocopherol) on 29,000 male Finnish smokers.(2) It had no impact ... on lung cancer, that is.

"In the men who took alpha-tocopherol, we saw a one-third reduction in the incidence of, and a 41 percent reduction in the death rate from, prostate cancer over a period of rive to eight years," explains Albanes, one of the ATBC study investigators.