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28.11.2008

Fish fatty acids keep prostate cancer under control

A high intake of fish and polyunsaturated n-3 fatty acids from fish cannot prevent men from getting prostate cancer. But it can halve the chance of dying from the disease. This is confirmed in the results of a big epidemiological study at Harvard, which were recently published in the American Journal of Clinical Nutrition.

Men have about a ten-percent chance of developing prostate cancer. So it's not surprising that doctors refer to the prostate as a ticking time bomb, and that scientists are searching for nutritional and lifestyle factors that reduce the chance of prostate cancer. In test-tube studies, fish fatty acids look as though they provide the ideal solution. A metabolite of the fish fatty acid EPA, 15-HEPE, inhibits the development of prostate cancer cells. But the epidemiological evidence to support the protective effect of fish fatty acids is weak: some studies suggest there is a relationship, others reject the possibility.

The Harvard researchers attempted to throw light on the matter by searching through a database of twenty thousand general physicians for data on the effect of fish and fish fatty acids on prostate cancer. The doctors were all participants in the Physician's Health Study, which started in 1983. At that point all were healthy and over forty, the oldest being eighty. The doctors told how much fish they ate, and the researchers monitored the participants for 22 years.

After analysing the data, the researchers concluded that eating fish did not prevent the doctors from developing prostate cancer. There was no link between the chance of contracting prostate cancer and the intake of fish fatty acids.

In the table above the researchers set the chance of developing cancer among the men who consume the least amount of fish fatty acids (quintile 1) at 1 (the referent). The men in quintile 3 had an average intake of fish fatty acids, and the men in quintile 5 the highest intake.

As the table shows, there was no effect.

But when the researchers looked at the likelihood of the men dying from prostate cancer, they did find a relationship. The more fish fatty acids the men consumed, the lower the chance of dying (see graph below). The steeper the curve, the greater the likelihood that men who have been diagnosed with prostate cancer will die from the disease.

If you look at intake of fish instead of fish fatty acids, the graph is almost identical. The group of men with the highest fish consumption - more than five times a week – were about half as likely to die of prostate cancer compared with the men who ate the least fish.

Sources:
Am J Clin Nutr. 2008 Nov;88(5):1297-303.