The study by scientists at the Fred Hutchinson Cancer Research Center, Seattle, US, found that men who consumed four or more glasses of red wine per week reduced their risk of prostate cancer by 50 per cent.
"Among men who consumed four or more 4-ounce glasses of red wine per week, we saw about a 60 per cent lower incidence of the more aggressive types of prostate cancer," said Janet Stanford, senior author of the study. "The more clinically aggressive prostate cancer is where the strongest reduction in risk was observed."
However, Stanford and her colleagues found that neither beer, hard liquor or white wine had any significant effect on the disease, leading them to believe that once again the antioxidant resveratrol, is the key to the puzzle.
The researchers were keen to point out that these results did not mean that men now had a licence to drink as much red wine as they wanted. Stanford emphasized that the risk of prostate cancer decreased six percent for every glass of red wine consumed per week, but research showed the law of diminishing returns comes into play when consumption increases beyond moderation.
"From a public-health standpoint, it's difficult to recommend any alcohol consumption given the risks associated with heavy consumption," said Stanford. "But for men who already are consuming alcohol, I think the results of this study suggest that modest consumption of red wine - four to eight 4-ounce drinks per week - is the level at which you might receive benefit."
For the study, the researchers interviewed 753 newly diagnosed Seattle-area prostate-cancer patients as well as 703 healthy controls.
"Even though this study is based on relatively small numbers, the results are intriguing and suggest that the potential beneficial effect of red wine and resveratrol - if indeed resveratrol is the active chemopreventive agent involved - would be very important, as it's the more aggressive forms of prostate cancer than are most important to prevent," said Stanford.
She added that a particular strength of the study was the relatively young age - 40 to 64 - of the participants, with the majority being under 60.
"By focusing on men under 65, whose incidence of prostate cancer is much lower than that of older men, we can tease out the effect of a particular environmental exposure on cancer risk, such as wine consumption, more easily than if we were looking at men across the entire age range," said Stanford.
She noted that this was particularly true when studying complex diseases such as prostate cancer in which numerous genetic and environmental factors are thought to play a role.
The researchers concluded that a further strength of the study was that participants were asked about a variety of other risk factors for prostate cancer, such as diet, family history of cancer, screening for prostate cancer and tobacco use, all of which were taken into account and adjusted for when analyzing the data.
To date few studies have looked at the link between prostate cancer and alcohol intake, and according to the researchers there have been no consistent results.
"Some have shown an increase, some a decrease, and most no association whatsoever," said Stanford. "Part of the problem, we believe, is that few of the studies have attempted to sort out the effects of different types of alcohol intake over a man's lifetime."
The researchers now plan to seek funding to conduct a larger study to see if their results are confirmed. In collaboration with Norm Greenberg - also from Fred Hutchinson - they also plan to test the effects of resveratrol on mouse models of prostate cancer to see if giving mice this chemical compound will reduce the onset of prostate cancer and/or decrease the aggressiveness of the disease.
Prostate cancer is one of the biggest cancer killers in industrial countries and affects more than 500,000 men worldwide every year. This number is expected to increase with the ageing population.