Chalk up another health benefit tied to fish consumption. New research shows omega-3 fatty acids — in fish and fish oil — may lower the risk of breast cancer in postmenopausal obese women.

Penn State College of Medicine researchers believe the protection likely comes from the fatty acids' anti-inflammatory effects, said Andrea Manni, professor and division chief of endocrinology, diabetes, and metabolism who helped lead the study.

"Omega-3 fatty acids have an anti-inflammatory effect, so that's one of the reasons why we suspected it may be particularly effective in obese women," Manni said.

Past studies have suggested omega-3s protect against breast cancer, but the findings have been inconsistent. Other studies have found obesity is a major breast cancer risk factor in postmenopausal women, and scientists believe increased inflammation is an important underlying cause in this population.

Manni said the Penn research suggests normal-weight women have less inflammation than heavier women, and are therefore less likely to benefit from anti-inflammatory omega-3s.

The study, published online in the journal Cancer Prevention Research, involved 266 women who were prescribed the antiestrogen drug Raloxifene, the omega-3 drug Lovaza (or a combination of the two drugs), or no treatment at all. All of the women had high breast density — a known biomarker for breast cancer risk — and had a variety of weight levels.

At the conclusion of the two-year study, the researchers found that increasing levels of omega-3 in the blood were associated with reduced breast density — but only in women with a body mass index above 29, bordering on obesity.

Although Lovaza contains both of the fatty acids DHA (375 milligrams) and EPA (465 milligrams), only DHA blood levels were associated with breast density reduction. The researchers plan to test the effect of DHA alone in obese subjects, potentially in combination with weight loss, in a future trial.

"The finding supports the idea that omega-3s, and specifically DHA, are preferentially protective in obese postmenopausal women," Manni said. "This represents an example of a personalized approach to breast cancer prevention."

Manni added that, with obesity-related cancers on the rise, the findings could have implications beyond breast cancer.

The researchers noted a combination of Lovaza and a low dose of Raloxifene (30 milligrams) also helped reduce patients’ triglycerides and LDL "bad" cholesterol and boosted HDL "good" cholesterol.