Swedish women who ate fatty fish like salmon, mackerel and herring at least once a week had a significantly lower risk of kidney cancer compared to consumers of lean fish, researchers said on Tuesday.

The 15-year study found those who regularly ate fish containing lots of fish oil that is rich in omega-3 acids and Vitamin D had a 74 percent lower risk of getting kidney cancer compared to those who ate no fish at all.

Lean varieties such tuna, cod and fresh-water fish did not confer the same benefit.

Compared to lean fish, fatty fish have up to 30 times the amount of certain acids and up to five times the level of Vitamin D. The fatty acids have been reported to slow development of cancer and people with kidney cancer often have low levels of Vitamin D.

“The name fatty fish may frighten some people but this kind of fat is healthy so I would recommend to eat fatty fish, not lean, because you can get much more benefits,” said Alicja Wolk of the Karolinska Institute in Stockholm.

“Fatty fish per definition has also more calories but benefits are so overwhelming,” she said.

The researchers, writing in the Journal of the American Medical Association, did not indicate whether fatty fish might prevent other types of cancer.

Of more than 61,000 women in the study, ranging in age from 40 to 76, 150 developed kidney cancer.

In the United States, there is a one in 77 lifetime risk of kidney cancer, and 39,000 Americans expected to be diagnosed this year, according to the American Cancer Society. The disease is twice as common among men than women.