"We may be able to use EPA and DHA supplements while also reducing omega-6 fatty acids in the diet as a cancer prevention tool or possibly to reduce progression in men with prostate cancer," said lead researcher Professor William Aronson from the David Geffen School of Medicine at UCLA.
Over half a million news cases of prostate cancer are diagnosed every year world wide, and the cancer is the direct cause of over 200,000 deaths. More worryingly, the incidence of the disease is increasing with a rise of 1.7 per cent over 15 years.
The new study adds to a growing body of evidence linking an increased omega-3 to omega-6 intake ratio to improved health. In March researchers from the Paterson Institute, a cancer research institute funded by British charity Cancer Research UK and affiliated with the University of Manchester reported that omega 6 fats increased the spread of prostate tumour cells into bone marrow, while omega-3 fatty acids were seen to block this invasion (British Journal of Cancer, doi: 10.1038/sj.bjc.6603030).
The new research, published in the new issue of the journal Clinical Cancer Research (Vol. 12, Issue 15), adds to this subject by reporting that changing the ration of omega-3 to omega-6 in the typical Western diet might reduce prostate cancer tumor growth rates and PSA levels.
Prostate specific antigen (PSA) is a protein that is used as a marker for the disease - higher levels are associated with a higher risk of prostate cancer.
A special mouse model was used for hormone-sensitive prostate cancer that is said to closely mirror the disease in humans. The mice were divided into two groups, one fed a diet comprised of 20 percent fat with a healthy one-to-one ratio of omega-6 to omega-3 fatty acids, while the second group of mice was fed the same diet but with the fat derived from mostly omega-6 fatty acids.
Omega 6 fats are found in corn, safflower and other vegetable oils, nuts, seeds, and red meats.
"Corn oil is the backbone of the American diet. We consume up to 20 times more omega-6 fatty acids in our diet compared to omega-3 acids," explained Aronson.
At the end of the intervention period, the researchers reported that tumour cell growth rates had decreased by 22 per cent and PSA levels by 77 per cent in the group receiving a healthier balance of fatty acids compared with the group that received predominantly omega-6 fatty acids.
"This study strongly suggests that eating a healthier ratio of these two types of fatty acids may make a difference in reducing prostate cancer growth, ," said Aronson.
The most likely mechanism for the tumour reductions, say the researchers, is the role of metabolites of omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the omega-6 acid, arachidonic acid. These three fatty acids compete to be converted by cyclooxgenase enzymes (COX-1 and COX-2) into prostaglandins, which can become either pro-inflammatory and increase tumour growth, or anti-inflammatory and reduce growth.
Aronson and his co-workers found that levels of the pro-inflammatory prostaglandin (PGE-2) were 83 per cent lower in tumours in the omega-3 group than in mice on the predominantly omega-6 fatty acid diet.
This suggests that higher levels of DHA and EPA may lead to development of more anti-inflammatory prostaglandins.
While the study agrees and supports previous studies, also conducted in laboratories, human studies are needed, said the researchers, before any clinical recommendations can be made.
Aronson and his team are currently conducting a clinical trial with men who are undergoing prostate removal due to cancer to compare the effects of a low-fat diet using omega-3 supplements and a balanced Western diet.
If results of this small trial are positive, this will be followed by larger clinical trials, said Aronson.