In the latest report, published online on Jan. 31 in JAMA Cardiology, an international team headed by Dr. Robert Clarke of the University of Oxford analyzed the combined results of 10 trials of fish oil supplements involving 77,917 older adults at high risk for cardiovascular disease.

At doses ranging from 226 milligrams to 1,800 milligrams per day of omega-3 fatty acids, no significant protection against “major vascular events” was found overall among the participants or for any subgroup, like those with prior heart disease or diabetes.

While this does not necessarily mean the supplements are unhelpful, it does suggest a more nuanced consideration of who, if anyone, may benefit from taking fish oils and whether we all might be better off simply eating more fish, even though that too can have some downsides as well as benefits. (At the moment, I’m still doing both.)

For example, large predatory fish like shark, swordfish, king mackerel, tilefish and albacore tuna can contain high levels of methyl mercury, a toxin that would override any health benefit, especially for the developing brains of fetuses and young children as well as for adults, Dr. Nesheim and Marion Nestle, professor emerita of nutrition, food studies and public health at New York University, noted in 2014 in an editorial in the American Journal of Clinical Nutrition. (Levels of mercury and other contaminants in fish have since declined somewhat but are not negligible.)

However, in both observational studies and controlled clinical trials, eating fish was shown to foster optimal development of a baby’s brain and nervous system, prompting advice that pregnant women and nursing mothers eat more fish rich in omega-3s while avoiding species that may contain mercury or other contaminants like PCBs sometimes found in freshwater fish.

Another concern is the environmental cost that could result if people ate more fish, given that “many ocean fisheries are fully exploited or are in decline,” Drs. Nesheim and Nestle wrote. “In the face of limited supplies,” they added, the price of seafood would likely be “out of the reach of many consumers.”

The declining supplies and rising costs of wild-caught fish have spawned a worldwide explosion of fish farming, which also has its downsides. For example, marine organisms used to feed farmed fish can diminish this vital food supply for wild stock, and fish that escape from farms may change the gene pool of wild fish.