Study also finds that beta carotene may raise likelihood of aggressive prostate cancer
For the past 10 years, many clinicians have been advising men to boost the levels of lycopene in their diet because it could lower their risk for prostate cancer or recurrence for the disease. These recommendations were based on studies showing a protective effect between lycopene consumption and prostate cancer. A recently published study casts doubt on that advice.
Researchers reported in Cancer Epidemiology, Biomarkers & Prevention (2007;16:962-968) that lycopene does not effectively prevent prostate cancer. In fact, the investigators observed an association between beta carotene, an antioxidant related to lycopene, and an increased risk for aggressive prostate cancer.
The study is one of the largest to evaluate the role of blood concentrations of lycopene and other ca-rotenoid antioxidants in preventing prostate cancer. Study data were derived from over 28,000 men enrolled in the Prostate, Lung, Colo-rectal, and Ovarian (PLCO) Cancer Screening Trial, an ongoing, randomized National Cancer Institute trial to evaluate cancer screening methods and to investigate early markers for cancers.
“It is disappointing, since lycopene might have offered a simple and in-expensive way to lower prostate cancer risk for men concerned about this common disease,” said study investigator Ulrike Peters, PhD, MPH, as-sistant professor at the Fred Hutchinson Cancer Research Center and an assistant professor in the department of Public Health at the University of Washington in Seattle. “Unfortunately, this easy answer just does not work.”
Much of the previous research had suggested that a diet rich in lycopene protected against prostate cancer. For the past 5-10 years, this has spurred commercial and public interest in the antioxidant. Antioxidants protect against free radicals, highly active atoms and molecules that can damage DNA and other important molecules in cells. Free radical damage increases with age, so the scientific community has harbored suspicion that this damage could increase the risk of prostate cancer, a disease that has been clearly associated with age.
In the last couple of years, however, studies of the potentially protective role of lycopene have been contradictory or inconclusive. In a 2006 study, Dr. Peters and her colleagues looked at the dietary intake of more than 25 tomato-based foods, using data from the PLCO trial, and found no overall association between lycopene intake and prostate cancer.
In the new study, the researchers followed more than 28,000 men aged 55-74 years with no history of prostate cancer. The men were initially screened with a PSA test and digital rectal examination and then were followed with routine examinations and screenings until first occurrence of prostate cancer, death, or the end of the trial in 2001. At the beginning of the trial, men gave a blood sample and completed a questionnaire related to their health, diet, and lifestyle.
The researchers focused on non-Hispanic Caucasian men, as the small number of cases among other ethnic groups are currently too small to draw any conclusions. They found no significant difference between those who had prostate cancer and those who did not in relation to the blood concentration of lycopene. In addition, the researchers found a relationship between an increased risk of aggressive prostate cancer and beta carotene.
Dr. Peters said this was an unexpected observation that could have possibly been due to chance, but “beta carotene is already known to increase risk of lung cancer and cardiovascular disease in smokers. While it would be counterproductive to advise people against eating carrots and leafy vegetables, I would say to be cautious about taking beta carotene supplements, particularly at high doses.”
Commenting on the new findings, Martha Terris, MD, chief of urology at the Augusta (Ga.) VeteransAffairsMedicalCenter and a professor of urology at the Medical College of Georgia in Augusta, observed: “It may be like the selenium story. A lot of the things we know may be protective of prostate cancer in low levels, such as selenium, at higher doses may actually promote cancer growth.”
Much remains unknown about the various minerals and micronutrients in the body and how high doses of these compounds are metabolized. Dr. Terris said she usually tells her patients to stick with the recommended daily allotments of any nutritional supplement, and that getting nutrients from food is better than taking them in pill form.