Diet rich in fatty fish good for cognitive function

Dear Doctors: Our grandfather is having memory problems, and my mom is trying to get him to eat more fish. I know fish is called “brain food,” but my mom says she has heard on the news that fish keeps you from getting dementia. Is this true? What about fish and mercury?

Dear Reader: Research into a link between a diet rich in fatty fish and improved cognitive function dates back decades. The findings continue to point to a wide range of benefits, including improved eye, cardiovascular and brain health.

The research that has focused on the brain-related effects of consuming fish has found the benefits to be far-reaching. These include not only improvements to cognitive function, but also what appears to be protective effects to both brain volume and brain structure. Many of the studies have pointed to the omega-3 fatty acids that certain fish contain as a factor in these findings. And because all roads seem to lead to the gut, newer research has found a beneficial connection between a diet rich in fish and seafood and the gut microbiome.

Your mother is correct that some research has linked regular fish consumption to a reduced risk of Alzheimer’s disease. One study, in which researchers studied brain autopsies, found that individuals who had included fish as a regular part of their diets had fewer markers of Alzheimer’s disease than did those who ate little or no fish and seafood. And, while the individuals in that study who had consumed more fish did have elevated levels of mercury in their bodies, the accumulations were not high enough to pose a danger. The researchers also concluded that the potential benefits of a diet that includes fish outweighed the risks.

Elizabeth Ko, MD and Eve Glazier, MD

That said, mercury in fish is an important issue. It’s a toxic metal that, once consumed, is not eliminated from the body. Negative health effects of methylmercury, which is the form of the element that reaches us through seafood, can include neurological and genetic damage. Mercury is especially damaging to the developing human and to young children. For that reason, it is recommended that eating fish during pregnancy should be limited to two servings per week. The same precaution is true for young children, whose developing brains and nervous systems are at highest risk of the damaging effects.

The good news is that it’s possible to limit the intake of mercury by being selective about the type of seafood that you eat. Steer clear of regularly consuming larger and long-lived fish, such as swordfish, ahi and bigeye tuna, orange roughy, marlin and king mackerel. Their long lifespans allow them to accumulate larger amounts of mercury. Children are recommended to stick to light or skipjack tuna, with a limit of two servings a week. Seafood and fish such as salmon, ocean perch, shrimp, sardines, scallops, herring, whitefish and flounder are good choices. The FDA offers a good guide on the topic. Go to fda.gov and enter “advice about eating fish” in the search box.

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(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)


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