In the latest report, published online on JAMA Cardiology on January 31, an international team led by Dr. Robert Clarke of Oxford University presented the combined results of 10 studies of fish oil supplements that included 77,917 older adults at high risk for cardiovascular disease.

At doses of 226 milligrams to 1,800 milligrams of omega-3 fatty acids per day, no overall significant protection against “major vascular events” was found among participants or for a subgroup such as those with a history of heart disease or diabetes.

While this doesn’t necessarily mean that the supplements aren’t helpful, it does suggest a more nuanced consideration of who, if anything, may benefit from taking fish oils and whether it’s better for all of us to just eat more fish, even if this can have some disadvantages as well as advantages. (Right now I’m still doing both.)

For example, large predatory fish such as shark, swordfish, king mackerel, tilefish, and albacore tuna can be high in methylmercury, a toxin that would override any health benefits, especially for the developing brains of fetuses and young children, as well as adults, Dr. Nesheim and Marion Nestle, professor emeritus of nutrition, food studies, and public health at New York University, noted this in a 2014 editorial in the American Journal of Clinical Nutrition. (The levels of mercury and other contaminants in fish have decreased somewhat since then, but not negligible.)

However, in both observational and controlled clinical studies, eating fish has been shown to promote optimal development of a baby’s brain and nervous system, which has led to the suggestion that pregnant women and nursing mothers eat more fish that are rich in omega -3 fatty acids while avoiding species that may contain mercury or other contaminants like PCBs that are sometimes found in freshwater fish.

Another problem is the environmental costs that could arise if people eat more fish, as “many marine fisheries are fully exploited or in decline,” said Dr. Nesheim and Nestle wrote. “Given the limited supply,” they added, the price of seafood would likely be “out of reach for many consumers.”

The declining supply and rising cost of wild-caught fish have led to a worldwide explosion in fish farming, which also has disadvantages. For example, marine organisms used to feed farmed fish can reduce this vital food supply for wildlife populations, and fish that escape from farms can alter the gene pool of wild fish.

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