Omega-3 fatty acids have almost no effect, good or bad, on the risk for cardiovascular disease or cancer.
Those are the findings of two large studies, one an update in the Cochrane Database of Systematic Reviews and the second in the British Journal of Cancer, that combined data from dozens of randomized controlled trials.
In 28 high-quality trials covered in the Cochrane analysis, with durations ranging from one to more than seven years, pooled results showed little or no effect of omega-3 supplements on dying from any cause, dying from cardiovascular disease, cardiovascular events like heart attack or stroke, or heart rhythm disorders. There was low-quality evidence of a small effect on coronary heart disease mortality. The investigation showed little evidence of any benefit in the few trials that tested eating oily fish.
The analysis in the British Journal of Cancer showed no beneficial effect on cancer diagnosis or cancer death. But the review found that high doses of omega-3 supplements may very slightly increase the risk for prostate cancer and cancer death. The authors conclude that this slight increase is probably offset by small protective effects on cardiovascular disease.
The American Heart Association and the American Cancer Society both recommend omega-3s for reducing the risk of heart disease and cancer, but Lee Hooper, a reader in nutrition at Norwich Medical School who worked on both studies, said that the evidence does not support those recommendations.
“We’ve tried to get it right,” she said. “We’ve tried to make sure all the details are there. We’ve tried to check every way to make sure we’re not missing something. And all we see is these tiny harms and benefits that appear to balance each other out.”