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Omega-3 fish oil doesn't reduce risk for early signs of colon cancer, study finds

Those who took the supplement daily for several years developed as many polyps as non-users, researchers say.

By
Brian P. Dunleavy
Omega 3 fish oil supplements offer many health benefits -- just not in colon cancer prevention, study finds. Photo by frolicsomepl/Pixabay
Omega 3 fish oil supplements offer many health benefits -- just not in colon cancer prevention, study finds. Photo by frolicsomepl/Pixabay

Nov. 21 (UPI) -- Omega-3 fatty acids offer a lot of health benefits -- but protecting against colorectal cancers may not be one of them, a new study suggests.

In trial results published Thursday in the journal JAMA Oncology, researchers from the T.H. Chan School of Public Health at Harvard found that adding 1 gram per day of "marine" omega-3s -- in other words, fish oils -- and vitamin D3 to a healthy diet failed to reduce adults' risk for developing colon polyps, which are considered "precursors" for colon cancer.

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The so-called "VITAL" trial evaluated the effects of dietary supplementation with fish oils in more than 25,000 adults, roughly half of whom used the supplement, while the others were given a placebo. Approximately 2.3 percent of study participants in each group were eventually diagnosed with conventional adenomas -- or benign tumors, some with significant presence of cancer cells -- or serrated polyps over the course of trial.

"I think the overall health benefits of omega-3 fatty acids are well established," study co-author Mingyang Song, assistant professor in the Department of Epidemiology at Harvard T.H. Chan School of Public Health, told UPI. However, he added, what the results of the VITAL indicate is that "more research is needed" before it can be determined whether the supplement "can reduce cancer risk."

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Song and his colleagues enrolled 25,871 in their trial, splitting the group in half, with roughly equal distributions along racial and gender lines. Half of the participants were given 1 gram "marine" omega-3 fatty acid, or fish oil, daily along with vitamin D3. The others received a placebo.

The mean age of the study participants was approximately 67 years, and roughly half of the participants in each group were women. Approximately 20 percent of the participants in each group were African-American.

In all, 294 of the 12,933 people in the omega-3 group developed conventional adenomas, compared to 301 of the 12,938 in the placebo group. In addition, 174 cases of serrated polyps were reported in the omega-3 group, compared to 167 in the placebo group.

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Although the authors weren't able to confirm an overall benefit for omega-3 in reducing risk for colorectal cancer precursors, they did find that supplementation "appeared to be associated with lower risk of conventional adenomas among individuals with low plasma levels of omega-3" at the beginning of the study. Also, use of omega-3s seemed to benefit African-Americans -- in terms of reduced risk for colorectal cancer precursors -- more than in other racial/ethnic groups.

In general, fish oil supplementation "is unlikely to have a substantial influence on risk of colorectal cancer precursors," Song said. "However, adults with low omega-3 fatty acid levels and African Americans may benefit from supplementation."

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