TUESDAY, Sept. 19 (HealthDay News) -- The heart-healthy omega-3 fatty acids abundant in fatty fish like salmon and sardines may help protect your kidneys against cancer, new research suggests.

A large, 15-year Swedish study of women looked at fatty and lean fish consumption and the risk of kidney cancer. The finding: Those who ate high amounts of fatty fish -- more than one serving a week -- had 44 percent less risk for developing renal cell carcinoma (the most common form of kidney cancer) than those who did not consume any fish.

"That's substantial," said Eugenia Calle, director of analytic epidemiology for the American Cancer Society. "There is very little published on this topic -- it may be the only study to look at fatty fish and kidney cancer."

The findings were published in the Sept. 20 issue of the Journal of the American Medical Association.

Previous studies on fish consumption and cancer risk produced inconsistent results, Calle said, and they were limited in that they looked at all types of fish consumption. There has been some experimental data with animals and cells that suggest fatty fish, with their abundance of omega-3 fatty acids and Vitamin D, may protect against cancer, she added.

The Swedish study, led by Alicja Wolk of the Karolinska Institutet in Stockholm, "is probably the first study to look at fatty fish consumption. There's a lot of hypotheses but not a lot of studies yet," Calle said.

The study investigated the association between fatty-fish and lean-fish consumption and the incidence of kidney cancer in 61,433 women. Fatty fish included salmon, herring, sardines, and mackerel; lean fish included cod, tuna and fresh water fish; and seafood included shrimp, lobster and crayfish. The participants answered a food frequency questionnaire when they entered the study in 1987 and in September 1997.

During an average 15-year follow-up from 1987 to 2004, 150 kidney-cancer cases were diagnosed. The researchers found a lower incidence of kidney cancer in women who ate fatty fish once a week or more, but found no association with lean fish or other seafood consumption.

"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 (renal cell carcinoma) 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 wrote in a prepared statement.

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

The Swedish researchers noted 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 are 20 to 30 times higher in fatty cold-water fish than in lean fish. Fatty fish has three to five times higher content of vitamin D than lean fish, and lower serum vitamin D levels have been associated with development and progression of renal cell carcinoma."

The Swedish findings conflict with a major review published earlier this year that found omega-3 fatty acids derived from fish or fish-oil supplements did not prevent cancer.

A review of more than 38 studies found no evidence that diets rich in fish fight any kind of malignancy. These conflicting data showed omega-3 fatty acids "definitely have health benefits, but they are not a panacea. Preventing cancer is not one of the things omega-3 fatty acids do," said lead researcher Dr. Catherine MacLean, a natural scientist at Rand Health and a rheumatologist at the Greater Los Angeles VA Healthcare System. The study was published Jan. 25 in the Journal of the American Medical Association.

Kidney cancer isn't that common in the United States, Calle said, ranking No. 7 for men and not making the top 10 cancers for women. "This is not a common cancer, so the public health impact is not as great as it would be, say, for breast, lung, prostate," she said. But, in terms of general interest, "if [fatty fish] were associated with a decreased risk of additional cancers, that would be a very important message."

"You can't go wrong eating fish," Calle said, adding that the American Cancer Society does not have specific recommendations on the type of fish to eat. "As more data become available, our dietary recommendations are reviewed and updated.

More information

For more on the health benefits of omega-3 fatty acids, visit the University of Maryland.