Men with high blood levels of docosahexaenoic acid (DHA), an inflammation-lowering omega-3 (ω3) fatty acid commonly found in fatty fish, have more than double the risk of developing aggressive, high-grade prostate cancer, according to a new study.

Researchers at Fred Hutchinson Cancer Research Center (Seattle, WA, USA) conducted a nested case-control analysis of 3,461 patients (age 55-84 years) participating in the US national Prostate Cancer Prevention Trial in the period 1994-2003. The 1,658 study cases were frequency matched to 1,803 controls by age, treatment, and prostate cancer family history. Phospholipid fatty acids were extracted from serum, and concentrations of ω3, ω6, and trans-fatty acids (TFAs) were expressed as proportions of the total. Estimated odds ratios were calculated for associations of fatty acids with prostate cancer by grade.

The results showed that DHA was positively associated with high-grade disease. Conversely, men with the highest blood ratios of TFAs--which are linked to inflammation and heart disease and abundant in processed foods that contain partially hydrogenated vegetable oils--had a 50% reduction in the risk of high-grade prostate cancer. The researchers also found that ω6 fatty acids, which are found in most vegetable oils and are linked to inflammation and heart disease, were not associated with prostate cancer risk; and none of the fats was associated with the risk of low-grade prostate cancer. The mechanisms behind the impact of ω3 on risk of high-grade prostate cancer are unknown. The study was published in the June 15, 2011, issue of the American Journal of Epidemiology.

“We were stunned to see these results and we spent a lot of time making sure the analyses were correct,” said lead author Theodore Brasky, PhD, a postdoctoral research fellow in the health sciences division. “Our findings turn what we know – or rather what we think we know – about diet, inflammation, and the development of prostate cancer on its head and shine a light on the complexity of studying the association between nutrition and the risk of various chronic diseases.”

Omega-3s are essential unsaturated fatty acids with a double bond (C=C) starting after the third carbon atom from the end of the carbon chain. They cannot be synthesized by the human body but are vital for normal metabolism. Nutritionally important ω3 fatty acids include α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), all of which are polyunsaturated. Common sources of ω3 fatty acids include fish oils and some plant oils such as flaxseed oil and algal oil.

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