Eating omega-3 rich fatty fish at least once a week lowered women's risk of renal cell carcinoma, while lean fish and crustaceans - shrimp and lobster - offered no benefit, explaining the inconsistent results of previous studies analyzing total fish consumption.
In this population-based prospective study performed in Sweden, over 61,000 women between 40 and 76 years old filled out a food frequency questionnaire when first entering the study, then seven to 10 years later. After adjusting for potential confounding factors, there was an inverse relationship with consumption of fatty fish such as salmon, mackerel and herring and risk of developing abnormal cellular growth within the kidney.
The study found that women who ate fatty fish once a week or more had a 74% reduction in developing abnormal cellular growth within the kidneys compared to those who didn't eat any fish at all. Interestingly, lean varieties of fish didn't provide the same benefit. Fatty fish can have up to 30 times the omega-3 fatty acids and up to five times the level of vitamin D compared to lean fish. The study concluded that the consumption of fatty fish may reduce the occurrence of this abnormal cellular growth in the kidney in women.
A preliminary study found that women who consumed one or more servings of fatty cold-water fish per week during an average of 15.3 years had a statistically significant 44% decreased risk of renal cell carcinoma compared with women who ate no fish, according to a report in the Sept. 20 2006 issue of the Journal of the American Medical Association. During 940,357 person-years of follow-up, there were 150 incident cases of renal cell carcinoma.
For a subset of women with consistent long-term consumption of fatty fish at baseline and 10 years later (one to three servings a month or more), the risk was down 74%, said Alicja Wolk, D.M. Sc., of the Karolinska Institute, and colleagues.
Fatty fish included salmon, herring, sardines, mackerel and krill. Lean fish included mainly cod, tuna, and sweet-water fish, as well as seafood such as shrimp, lobster, and crayfish.
The findings came from the Swedish Mammography Cohort, a population-based prospective cohort study of 61,433 women, ages 40 to 76, without a previous diagnosis of cancer at baseline (March 1, 1987 to Dec. 14, 1990). Participants filled out a 67-item food-frequency questionnaire at baseline and in September 1997.
No previous study has investigated the association between fatty fish and lean fish specifically and the risk for renal cell carcinoma, Dr. Wolk said. Previous studies of kidney cancer risk and fish consumption have had inconsistent results and have analyzed total fish consumption not taking into account the large differences between lean and fatty fish in the content of omega-3 fatty acids and vitamin D, she added.
Compared with lean fish, fatty cold-water fish have up to a 20- to 30-times higher content of marine omega-3 polyunsaturated fatty acid, eicosapentaenoic acid, and docosahexanoic acid, all of which have been reported to slow cancer development.
Also, the vitamin D levels in fatty fish are three to five times higher than in lean fish, while lower serum vitamin D levels have also been linked to the development and progression of renal cell carcinoma, the researchers wrote.
As for the role of vitamin D, the researchers suggested that low serum levels of vitamin D3, plentiful in fatty fish, may influence the development and progression of renal cell carcinoma. Vitamin D3 exerts its biological activity by binding to the vitamin D receptors, which are present in kidney cells. The vitamin D receptor genotype, they said, may play an important role in determining the risk of developing more aggressive kidney cancer.
Wolk, A. et al, "Long-term Fatty Fish Consumption and Renal Cell Carcinoma Incidence in Women" JAMA 2006; 296:1371-1376.