Taking supplements of lycopene, the tomato-derived carotenoid making growing sales in the supplement market, may not be sufficient to fight against the onset of prostate cancer, say researchers in a new study.
The antioxidant, also responsible for the red colour of tomatoes and other fruits, has been linked to reduced risk of prostate cancer in studies. It is marketed increasingly in supplement form but the new findings, based on a comprehensive prostate-cancer survival study done on rats, found that it may be more powerful in combination with other phytochemicals in tomatoes.
"It has been unclear whether lycopene itself is protective. This study suggests that lycopene is one factor involved in reducing the risk of prostate cancer," said John Erdman, professor of food science and human nutrition and of internal medicine at the University of Illinois, US.
"This also suggests that taking lycopene as a dietary supplement is not as effective as eating whole tomatoes. We believe people should consume whole tomato products - in pastas, in salads, in tomato juice and even on pizza."
Researchers now suggest that the lycopene found in human prostate tissue and the blood of animals and humans who remain disease free may reflect heightened exposure not just to lycopene but also to other compounds that may be working in synergy with it.
For the 14-month study, published in today's Journal of the National Cancer Institute, the Illinois team randomly assigned 194 male rats treated with a carcinogen to induce prostate cancer to diets containing whole tomato powder (made from tomato paste that included seeds and skins), pure lycopene or a control.
Four weeks later, the rats were divided into two groups, with one having unlimited access to food and the second consuming 80 per cent of the first's average daily intake. At the conclusion of the feeding portion of the study, histological studies on all of the rats' tissues and blood were done at Ohio State University.
Researchers found that the rats that had consumed the tomato powder had a 26 per cent lower risk of prostate cancer death than control rats, after controlling for diet restriction. The rats fed pure lycopene had a risk of prostate cancer similar to control rats.
"Tomato powder consumption clearly extended the life and reduced the cancer in this particular model," Erdman said. "Lycopene was a little better than the control group but not as good as the tomato powder group."
In the end, prostate cancer had claimed the lives of 80 percent of the control group, 72 per cent of the lycopene-fed rats and 62 per cent of the rats fed tomato powder. Rats on the restricted diet had an even lower risk of developing prostate cancer, independent of their diets. The researchers suggest that tomato products and diet restriction may have independent additive benefits.
Other unpublished data in cell culture studies support the idea that lycopene's role is enhanced in the presence of other phytochemicals in tomatoes, Erdman said. More work is needed to understand the role of the various phytochemicals in tomatoes and to determine whether there are additive or synergistic effects among the compounds.
"Our findings strongly suggest that risks of poor dietary habits cannot be reversed simply by taking a pill," said Professor Stephen Clinton, from Ohio State University. "We shouldn't expect easy solutions to complex problems. We must focus more on choosing a variety of healthy foods, exercising and watching our weight." He added: "Our study does not say that lycopene is useless. Instead it suggests that if we want the health benefits of tomatoes, we should eat tomatoes or tomato products and not rely on lycopene supplements alone."
The authors of the study conclude: "Many men are consuming lycopene-containing supplements with the hope that they may prevent prostate cancer or enhance the treatment of their prostate cancer. We suggest that a focus on interventions with whole tomato products and energy balance should be a priority while clinical studies simultaneously investigate the risks and benefits of lycopene supplementation."
While the study raises doubts about the use of lycopene supplements, more research could pave the way for development of tomato products or extracts to work against the onset of prostate cancer.
In an accompanying editorial, Peter H. Gann, of the Robert H. Lurie Comprehensive Cancer Center at Northwestern University in Chicago, and Frederick Khachik, of the University of Maryland, College Park, note that the study adds to the debate about whether cancer prevention is best achieved with whole foods or with single compounds. They point out that carotenoids and other secondary plant compounds evolved as sets of interacting compounds, and say that this complexity limits the usefulness of reductionist approaches that seek to identify single protective compounds.