by Craig Weatherby
The very productive team of Swedish scientists at Stockholm’s Karolinska Institute struck again this week, with publication of another data analysis from their series of epidemiological (population) studies on cancer risk factors.
We’ve reported several other of their findings as well… see, for example, “Cancer-Risk Findings Rank Seafood and Poultry Far Safer than Processed Meats.”
This time, they were looking at risk of prostate cancer, which afflicts Swedish men at high rates, compared with men in East Asian countries.
Past studies generally suggest that higher fish intake reduces prostate cancer risk, although the average association is relatively weak. And one anomalous study in Japanese men indicated an increased risk (Allen NE 2004): an outcome evern the researchers discounted as improbable.
Study finds a big risk reduction, but with a genetic distinction
The Swedes queried 1,500 men diagnosed with prostate cancer about their diets, and compared the answers with a healthy control group.
The results indicate that men who eat salmon more than once a week are 43 percent less likely to develop prostate cancer, in comparison with men who never eat salmon.
However, not all the salmon-eating men benefited from the fish equally.
Blood tests showed that 60 percent of the salmon-eating men benefited dramatically from eating fatty fish regularly, probably because they had a particular variant of the gene that controls activation of the pro-inflammatory COX-2 enzyme.
Prostate cancer growth is spurred by inflammation, and the risk among the salmon eaters with this variation of the COX-2 gene was a whopping 72 percent lower than for the men who never ate fatty fish.
It's likely that the omega-3s ingested by the men with this genetic variation caused the COX-2 enzyme to create more anti-inflammatory prostaglandins than in the other men.
Prostaglandins are ephemeral, hormone-like substances, some of which are anti-inflammatory, others of which are pro-inflammatory. Dietary omega-3s from fish induce creation of anti-inflammatory prostaglandins via their influence on the genes that control the COX-2 enzyme.
Interestingly, the yellow pigment in turmeric (curcumin) also exerts anti-inflammatory, COX-2-mediated effects, which is why it slows prostate cancer growth in cell studies.
Lead author Maria Hedelin, Ph.D. opined that it makes sense to eat fatty fish, even though 40 percent of men lack the “protective” variant of the gene.
As she said, “This study shows that there is an interaction between dietary factors and our genes, but it’s always hard to say what role the genes play. Omega-3 fatty acids can still be good for men who don’t carry this gene variant in completely different ways.”
- Hedelin M, Chang ET, Wiklund F, et al. The association of frequent consumption of fatty fish with prostate cancer risk is modified by COX-2 polymorphism. International Journal of Cancer Online October 25 2006, DOI 10.1002/ijc.22319
- Terry P, Lichtenstein P, Feychting M, Ahlbom A, Wolk A. Fatty fish consumption and risk of prostate cancer. Lancet. 2001 Jun 2;357(9270):1764-6.
- Augustsson K, Michaud DS, Rimm EB, Leitzmann MF, Stampfer MJ, Willett WC, Giovannucci E. A prospective study of intake of fish and marine fatty acids and prostate cancer. Cancer Epidemiol Biomarkers Prev. 2003 Jan;12(1):64-7.
- Terry P, Wolk A, Vainio H, Weiderpass E. Fatty fish consumption lowers the risk of endometrial cancer: a nationwide case-control study in Sweden. Cancer Epidemiol Biomarkers Prev. 2002 Jan;11(1):143-5.
- Allen NE, Sauvaget C, Roddam AW, Appleby P, Nagano J, Suzuki G, Key TJ, Koyama K. A prospective study of diet and prostate cancer in Japanese men. Cancer Causes Control. 2004 Nov;15(9):911-20.