TUESDAY, May 24 (HealthDay News) -- Long known as heart-healthy, fish that's baked or broiled also protects against developing heart failure, a new study suggests.

Research tracking more than 84,000 postmenopausal women for an average of 10 years found that those whose diets included more baked and broiled fish -- defined as five or more servings per week -- had a 30 percent lower risk of heart failure compared to women who ate less than one serving per month.

"A direct relationship between fish and heart failure is not necessarily intuitive because you might expect it protects against heart attacks," said senior study author Dr. Donald Lloyd-Jones, a preventive cardiologist and chair of the department of preventive medicine at Northwestern University Feinberg School of Medicine, in Chicago. "But that's not the mechanism in place here . . . and I think that's kind of interesting. It's also interesting that how you prepare fish is just as important as the kind of fish you're eating."

The study is published May 24 in the journal Circulation: Heart Failure.

Eating fried fish -- previously tied to greater risks for strokes -- is linked to a higher danger of heart failure, the study found, with even one serving per week associated with a 48 percent greater risk.

Additionally, dark fish such as salmon, mackerel and bluefish were associated with lower risks than either tuna or white fish such as sole, snapper or cod.

Prior research has suggested that omega-3 fatty acids in fish reduced risks for cardiovascular disease by lowering inflammation and improving blood pressure and cardiac and blood vessel function.

Lloyd-Jones said his study showed no specific link between omega-3s and heart failure, as compared to overall heart disease, but noted that science is still teasing out all the nutritional aspects of fish. Heart failure is characterized by the inability of the heart to pump sufficient blood to the rest of the body.

"We may not know the other components . . . but that's why eating fish is better than taking a supplement," he said. "You really need to eat the food. This is clearly an important part of a healthy dietary eating pattern."

Lloyd-Jones' study was based on data from 84,493 women aged 50 to 79 from the Women's Health Initiative study. The vast majority of participants were white (85 percent), while 7 percent were black and 3 percent were Hispanic.

The main limitation of the study was its observational nature and the self-reported eating habits of participants, said Lona Sandon, an assistant professor of clinical nutrition at the University of Texas Southwestern in Dallas.

"What we don't know is have these women been eating five servings of baked and broiled fish all of their lives, or is this something they started in their fifties?" Sandon said. "They may also have a more active lifestyle and eat less saturated fat. So there are a lot of differences, probably, in overall nutrition intake."

Indeed, the study indicated that participants whose diets included more baked and broiled fish tended to be healthier and younger than peers who ate fried fish, as well as more physically active and fit. They were also more educated, less likely to smoke and had fewer incidences of diabetes, high blood pressure and cardiovascular disease.

"Certainly it's promising that [baked and broiled fish] essentially had a protective effect," Sandon said. "That goes along with what we know in other studies - something about fish is good for us. Something about unfried fish is good for us as well."

More information

The U.S. National Institutes of Health has more on heart failure.