There is already some evidence to show that lycopene, the antioxidant found in tomatoes, could both protect against onset of prostate cancer and slow the growth of tumours.
A new study suggests that green and black tea polyphenols, already shown to fight other cancers, could slow the growth of prostate cancer cells. And the polyphenols appear to be quickly absorbed in human prostate tissue, according to the researchers at the University of California at Los Angeles. They were able to detect the compounds in prostate tissue after a very limited consumption of tea.
More importantly, the scientists found that prostate cancer cells grew more slowly when placed in a medium containing blood serum of men who had consumed either green or black tea for five days compared to serum collected before the men began their tea-drinking regimen. Serum from men who drank comparable amounts of diet or regular soda showed no such slowing in cancer cell proliferation, they reported at this week's Experimental Biology meeting in Washington DC.
Prostate cancer is one of the common cancers among men, and in the US it is known that at least a quarter of all prostate cancer patients use alternative therapies, including green tea.
Other natural products shown to fight growth of prostate cancer cells include the mineral selenium, the soy compound genistein (thought to reduce prostate-specific antigen levels), and a chemical produced when digesting green vegetables like broccoli and kale, called 3,3'-diindolylmethane (DIM). All of these need to go through further human clinical trials before lab findings can be confirmed.
The UCLA researchers noted that recent animal and epidemiological studies suggest that tea may have anti-tumour effects against carcinoma of the prostate, and many of the polyphenolic components of tea have been found in the prostate and many other tissues in rats and mice after chronic consumption of green tea polyphenols in drinking water.
In the new study, Dr Susanne Henning and colleagues focused on the possible effect of tea polyphenols on factors named polyamines and the enzymes responsible for the production of polyamines. Elevated levels of polyamines have been associated with malignancy in humans, including prostate cancer, and - since polyamines are present in prostate tissue in high concentration - are considered a logical target for chemoprevention of prostate cancer.
Five days before they were to undergo radical prostatectomy, 20 men with prostate cancer were randomly assigned to consume daily either five cups of green tea, five cups of black tea, or diet or regular soda containing no tea polyphenols. Their blood serum was then collected and added to prostate tissue samples from a commercially available prostate cancer cell line called LNCaP.
Analysis of the prostate tissue showed a large variation in tea polyphenol content between study participants. Tea polyphenols were found in six out of eight participants drinking green tea, seven out of seven drinking black tea, and two out of five drinking soda. The fact that two of the control participants showed polyphenols in the prostate sample might be because they were eating chocolate regularly (which contains the polyphenols epicatechin and epicatechingallate) or drinking tea before entering the study, suggested the researchers.
But two important factors were different in the men who drank tea and those who did not during the five-day study.
When the scientists compared the level of total polyamine to the total polyphenol content, the tea drinkers showed a significant negative correlation - the more tea components in the tissue, the less of the polyamines associated with malignancy.
And when the scientists measured the proliferation of prostate cancer cells, there was a significant decrease in how fast new cancer cells appeared for the men who had consumed either green or black tea. That was true even when no tea components could be detected in the serum, indicating that the inhibition of cell proliferation was caused by other compounds altered through tea consumption, said Dr Henning.
Both black and green tea are therefore promising natural dietary supplements for chemoprevention of prostate cancer, according to Dr Henning. She plans to investigate if this effect can be enhanced by consuming larger amounts of tea polyphenols in the form of green tea extract supplement capsules.