Tomato Antioxidant Does Not Prevent Cancer

September 2007 - A recent study by researchers based at the National Cancer Institute and Fred Hutchinson Cancer Research Center published in Cancer Epidemiology, Biomarkers & Prevention concludes that lycopene, an antioxidant predominately found in tomatoes, is not effective in preventing prostate cancer. In addition, the study found an unexpected association between beta-carotene, a related antioxidant, and an increased risk of aggressive prostate cancer.

Described as one of the largest of its type, the study by Dr Ulrike Peters and colleagues was based on data from over 28 000 men enrolled in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial which evaluates cancer screening methods and investigates early markers of cancer.

Ulrike Peters said:

"It is disappointing, since lycopene might have offered a simple and inexpensive way to lower prostate cancer risk for men concerned about this common disease. Unfortunately, this easy answer just does not work."

Researchers explain that antioxidants protect against free radicals, highly reactive atoms and molecules that can damage DNA and other cellular components. Like the incidence of prostate cancer, free radical damage increases with age. Previous research suggesting that a diet rich in lycopene protected against prostate cancer stimulated commercial and public interest. However, subsequent studies proved contradictory or inconclusive. In a 2006 study, Ulrike Peters and colleagues used data from the PLCO trial to evaluate dietary intake of more than 25 tomato-based foods and found no overall association between lycopene intake and prostate cancer.

The 28 000 men in the current study were between the ages of 55 and 74 with no history of prostate cancer. They were initially screened using a PSA test and digital rectal examination and completed a questionnaire related to health, diet and lifestyle. They were followed through routine screenings until first occurrence of prostate cancer, death or the end of the trial in 2001.

Researchers focused on non-Hispanic Caucasian men, the only statistically significant ethnic group. They found no significant difference between those who had prostate cancer and those who did not in relation to the concentration of lycopene in their bloodstream.

Ulrike Peters commented:

"Our results do not offer support for the benefits of lycopene against prostate cancer."

She added that the most unexpected finding was the relationship between increased risk of aggressive prostate cancer (defined as disease that has spread beyond the prostate) and beta-carotene, another antioxidant found in many vegetables and a common dietary supplement.

Ulrike Peters concluded:

"This may be due to chance however beta carotene is already known to increase risk of lung cancer and cardiovascular disease in smokers. While it would be counter-productive to advise people against eating carrots and leafy vegetables, I would say to be cautious about taking beta carotene supplements, particularly at high doses, and consult a physician."

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