Renal cell carcinoma (RCC) involving the renal parenchyma (the functional tissue of the kidney) accounts for more than 80 percent of all kidney cancers. Renal cell carcinoma incidence rates in the United States had been increasing in 1970-1990s, especially among black women and men; more recent data suggest a leveling off in this trend for most racial groups. The evidence that fish consumption, especially fatty fish, may be associated with lower risk of several cancers has not been consistent, according to background information in the article.

Previous studies have analyzed total fish consumption and have not taken into account that there are large differences between fatty fish and lean fish in the content of omega-3 fatty acids and vitamin D. Marine omega-3 polyunsaturated fatty acids, eicosapentaenoic acid and docosahexaneoic acid, which are present in significant amounts in fatty cold-water fish (up to 20-30 times higher content than in lean fish), have been reported to slow the development of cancer. Fatty fish has 3 to 5 times higher content of vitamin D than lean fish, and lower serum vitamin D levels have been associated with development and progression of RCC.

Alicja Wolk, D.M.Sc., of the Karolinska Institutet, Stockholm, Sweden and colleagues investigated the association between fatty fish and lean fish consumption and the risk for development of RCC in a population with a relatively high consumption of fatty fish. The participants, from the Swedish Mammography Cohort, included 61,433 women age 40 to 76 years without previous diagnosis of cancer at baseline (March 1987 to December 1990). Participants filled in a food frequency questionnaire at baseline and in September 1997. The researchers considered fatty fish to include salmon, herring, sardines, and mackerel; lean fish included cod, tuna, and sweet water fish; and other seafood included shrimp, lobster, and crayfish.

During an average of 15.3 years of follow-up between 1987 and 2004, 150 RCC cases were diagnosed. After adjustment for potential confounders, an inverse association of fatty fish consumption with the risk of RCC was found, while no association was found with the consumption of lean fish or other seafood.

"In this large population-based cohort with data on long-term diet, we found that women who consumed one or more servings of fatty fish per week had a statistically significant 44 percent decreased risk of RCC compared with women who did not consume any fish. Women who reported consistent long-term consumption of fatty fish at baseline and 10 years later had a statistically significant 74 percent lower risk," the authors write.

"Our results support the hypothesis that frequent consumption of fatty fish may lower the risk of RCC possibly due to increased intake of fish oil rich in eicosapentaenoic acid and docosahexaneoic acid as well as vitamin D," they write. "Our results, however, require confirmation because this is the first epidemiological study addressing this issue."

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