Tomato Diet Can't Guarantee Prostate Health: Study

But Alan Kristal, associate head of the Cancer Prevention Program at the Fred Hutchinson Cancer Research Center in Seattle, remained more skeptical. Though he called the study "well-executed," Kristal noted, for instance, that the authors were unable to control for prostate-specific antigen (PSA) testing among the men. These blood tests often detect clinically irrelevant tumors, he explained.

"You can never do an observational study of prostate cancer without rigorously controlling for whether or not the person got PSA screening," Kristal said. "The more times you take the test, the more likely you are to get the disease."

He also noted that the finding for lycopene contradicts a report published in May inCancer Epidemiology Biomarkers and Prevention. That study did account for PSA testing, and it found no effect of lycopene whatsoever on prostate cancer risk -- including the risk of advanced disease.

"To my mind, that study is definitive," said Kristal. "It's a big study, extremely well executed, properly analyzed, and not biased by PSA screening."

A review of lycopene's effect on cancer by the U.S. Food and Drug Administration, published in July in theJournal of the National Cancer Institute, likewise found "no credible evidence to support an association between lycopene intake and a reduced risk of prostate, lung, colorectal, gastric, breast, ovarian, endometrial, or pancreatic cancer and very limited evidence to support an association between tomato consumption and reduced risks of prostate, ovarian, gastric, and pancreatic cancers," according to that study's authors.

So, with tomatoes, ketchup and pizza sauce crossed off the list of prostate-protecting foods, Key and others continue the search. Kristal, for instance, is on the executive committee of a randomized trial examining the effects of selenium and/or vitamin E on prostate cancer risk in 35,000 men. Results are expected in 2012, he said.

Said Key, "I am optimistic we will find something. This paper is an important piece of work, but it doesn't look like this is the answer."

More information

For more on vitamins and cancer, visit the American Cancer Society.

SOURCES: Tim Key, Ph.D., deputy director, Cancer Research UK Epidemiology Unit, University of Oxford, U.K.; Peter Scardino, M.D., chairman, department of surgery and head, Prostate Cancer Program, Memorial Sloan-Kettering Cancer Center, New York City; Alan Kristal, DrPH, member and associate head, Cancer Prevention Program, Fred Hutchinson Cancer Research Center, Seattle; September 2007,American Journal of Clinical Nutrition