More good news if you're a fan of particular fish: eating salmon, herring, mackerel and sardines may help you keep your kidneys at peak performance, but cod, tuna, shrimp, lobster and crayfish probably won't.

Swedish doctors say omega-3 acids in "fatty fish" may not only protect your heart but your kidneys from renal cell carcinoma, the most common form of kidney cancer.

But "lean fish," which is much lower in omega-3 acids,  fails to give you such benefits, according to the 15-year study of more than 61,000 women by researchers at Stockholm's Karolinska Institutet, a medical university where the Nobel Prize in medicine is awarded each year.

Health experts note that the study only links lower kidney-cancer risks and fatty-fish eating, and doesn't prove a cure, but adding fatty fish to your healthy eating plans still can't hurt you.

Separating fat from lean

Although other studies looked at cancer and fish but with inconsistent results, the study by the institute's Dr. Alicja Wolk from 1987 to 2004 is believed by health experts to be the first to study fatty-fish consumption and separate fatty fish from their lean cousins.

Women who ate fatty fish consistently over the long haul were 74 percent less likely to get kidney cancer during the study's first 10 years and 44 percent for the entire 15 years, she said.

Wolk and her team noted that fatty cold-water fish contain 20 to 30 times more omega-3 polyunsaturated fatty acids than lean fish. In addition, fatty fish's vitamin D content is three to five times higher than that  of lean fish.

Lower levels in the blood of vitamin D are linked to the development and progression of renal cell carcinoma, Wolk said.

Her findings contradict a study earlier this year that said that fish diets or fish-oil supplements fail to prevent cancer. The study reviewed more than 38 other studies that found no evidence between fish diets and any cancer, but they didn't differentiate between fatty and lean fish, Wolk said.

In the United States, kidney cancer is the seventh most prevalent cancer for men and is even lower for women, according to the American Cancer Society.

The study was published in the  Sept. 20 issue of the Journal of the American Medical Association.