December 18, 2014
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Nutrition and Fitness

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Study: Mercury in fish may not harm seniors' brain function

While eating fish is believed to be healthy, some seafood has gotten a bad rap over its mercury content. But should older adults - who may benefit from the heart-healthy fats contained in fish - pass up the seafood over concerns about their mercury levels? Research suggests that the answer may be no.

Fish has long been touted as an important part of a healthy diet thanks to its protein content and its levels of omega-3 fatty acids. These healthy fats have been linked to protection against heart disease, inflammation from arthritis, and depression as well as a wealth of other benefits. But concern over the mercury content in fish has caused many people to forgo it. Mercury has been linked to trouble with learning development and has been the subject of warnings for pregnant women and young children.

But a study in the Journal of the American Medical Association says older adults may not need to worry about the effects of too much fish on their brains. Researchers at the Johns Hopkins Bloomberg School of Public Health collected data from 474 randomly selected people between the ages of 50 and 70 who were participating in the larger Baltimore Memory Study. They measured the participants' blood mercury levels and had them complete questionnaires that included questions on diet and fish consumption, smoking, alcohol use, and other factors.

Participants then completed 12 tests focusing on memory, manual dexterity, verbal skills, and other cognitive markers. And researchers found that while higher blood mercury levels were linked with poorer recall and visual memory, they were also associated with better performance on a test of manual dexterity.

"We cannot exclude the possibility that these associations were due to chance," they wrote in their findings.

"Overall, the data do not provide strong evidence that blood mercury levels are associated with worse neurobehavioural performance in this population of older urban adults." However, they go on to add that since the study only involved a single blood test, further research is needed.

But while the study points to the safety of fish for older adults, Health Canada warns Canadians to limit their consumption of certain fish to one meal per week - and one per month for pregnant women, women of childbearing age, and young children.

Specifically, their warning concerns shark, swordfish, and fresh or frozen tuna (not canned), all of which have been shown to contain high levels of mercury. These fish are of particular concern because of their age and place in the food chain, which causes mercury to "bioaccumulate" or concentrate inside them in higher levels than in other fish.

Other fish and seafood such as salmon, cod, pollock, sole, shrimp, mussels, and scallops fall well below Health Canada's limits and can safely be eaten regularly.


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