The researchers from the University of California, Los Angeles, suggest that men diagnosed with prostate cancer and having already had preliminary treatment, may benefit from a daily dose of pomegranate juice by suppressing further growth and delaying the need for further therapies.
"In older men 65 to 70 who have been treated for prostate cancer, we can give them pomegranate juice and it may be possible for them to outlive their risk of dying from their cancer," said lead author Dr Allan Pantuck, Jonsson Cancer Center, UCLA.
The fruit, a rich source of antioxidants, has been linked to improved heart health, but other varied claims have been made including protecting against prostate cancer and slowing cartilage loss in arthritis.
It is these antioxidants, and particularly compounds like punicalagin, which accounts for about half of the fruit's antioxidant ability, that are behind the proposed anti-cancer effects observed in this new study.
The researchers recruited 46 men with recurrent prostate cancer and rising levels of prostate specific antigen (PSA) after surgery or radiotherapy. PSA levels, commonly used to screen for prostate cancer and for tracking the disease after its diagnosis, were between 0.2 and 5 nanograms per millilitre of serum.
Data was also available on PSA levels prior to the start of the pomegranate juice trial, enabling the researchers to calculated PSA doubling times (PSADT) - the time necessary for PSA levels to double, and a signal that the cancer is progressing. Doubling time is crucial in prostate cancer, Pantuck said, because patients who have short doubling times are more likely to die from their cancer
The men were given eight ounces (227g) of pomegranate juice (Wonderful variety, equivalent to 570 mg of polyphenols) every day, and followed in three-month intervals.
The researchers found that the average doubling time increased from an average of 15 months to 54 months for the men drinking the pomegranate juice.
The scientists also measured the effects on oxidative stress as a result of drinking the antioxidant-rich juice. It was found that drinking the pomegranate juice decreased measurable oxidative stress by 40 per cent, compared to baseline.
In vitro tests of the subjects before and after the pomegranate juice phase showed that there was a 12 per cent decrease in cell proliferation (spread of the cancer) and a 17 per cent increase in apoptosis (programmed cell death).
"We don't know yet the specific factors behind this response - that's our next step in this research. We want to find out what cell signaling pathways might be affected, what is happening to keep PSA levels stable," wrote Pantuck in the journal Clinical Cancer Research (Vol. 12, pp. 4018-4026).
One possible mechanism is that pomegranate juice exerts an anti-inflammatory effect. Chronic inflammation has been linked to the incidence of many cancers, say the researchers, including prostate.
"There are many substances in pomegranate juice that may be prompting this response. We don't know if it's one magic bullet or the combination of everything we know is in this juice. My guess is that it's probably a combination of elements, rather than a single component," said Pantuck.
The researchers were keen to stress that this is the first clinical trial of pomegranate juice in patients with recurrent prostate cancer, and that significant further study is required, including randomised, double-blind, placebo-controlled studies.
A larger Phase III study, headed up by UCLA, has already started (April 2006) and is being conducted at ten centers across the US. Pantuck said he has men on the study more than three years out who are not being treated for prostate cancer other than drinking pomegranate juice and their PSA levels continue to be suppressed.
"The juice seems to be working," he said.
Over half a million men worldwide are diagnosed with prostate cancer every year, with over 200,000 deaths from the disease. The lowest incidence of the cancer is in Asia and the Far East, in particular India and China.