The Risks of Mercury in Fish


In China, it is believed that eating fish will help make your wishes come true. In Celtic mythology, eating fish bestows a person with infinite knowledge. Indeed, in cultures and religions the world over, fish have been an enduring symbol of prosperity and divinity.

The Benefits

Of course, the merits of fish aren’t just metaphysical. Fish are a rich source of omega-3 fatty acids — good, unsaturated fats, which promote physical and mental wellbeing. Since 1996, the American Heart Association has advised eating fish regularly to improve cardiovascular health. The low-calorie, high-protein food improves heart health by lowering triglycerides and stemming arteriosclerosis. In the past decade, research has linked fish consumption to decreased risk of strokes, diabetes, diseases of the eye and some cancers as well. Eating fish can also reduce rates of Alzheimer’s disease and boost intelligence — a 2005 Harvard study showed that women who ate fish every week had children with higher intelligence scores than children of women who did not do so.

The Dangers of Mercury

While the advantages of regular fish consumption are clear, new evidence about the dangers of mercury has made the waters murkier. Mercury is a heavy metal found in both fresh and salt water that in high doses acts as a neurotoxin. While all fish contain traces of mercury, the mercury content in certain large, predatory fish — including tilefish, shark, swordfish and king mackerel — is high enough to warrant concern. The average person who eats more than one serving of these fish in a week will be exceeding the World Health Organization’s upper limit for weekly mercury consumption. Tuna, a popular choice for many fish eaters, has also come under scrutiny by the FDA. Vulnerable individuals, including pregnant women and children, are advised to limit intake of canned albacore tuna as well as tuna steaks to six ounces or one can per week. Fresh tuna, which is commonly used in sushi, was originally excluded from the FDA's advisory. But a recent study by The New York Times revealed tuna sushi to contain levels of mercury equal or greater to those in cooked tuna — levels high enough to permit the FDA to take legal action to remove the fish from the market.

Symptoms of Mercury Poisoning

Symptoms of mercury poisoning include motor impairments, muscle weakness, numbness in the extremities and memory loss. Though in many cases symptoms fade after mercury blood levels fall, exposure to excessive levels can permanently damage or fatally injure the brain and kidneys. Unsafe levels of mercury can also interrupt neurological development in fetuses, infants and children. Yet even when eating high-mercury fish doesn’t result in mercury poisoning per se, the health costs are still considerable. Studies suggest that mercury consumption may actually cancel out the cardiovascular benefits of omega-3s. One study done in Finland showed that men who consumed high-mercury fish had double the rates of heart attacks and strokes than men who did not eat such fish.

Consume in Moderation

So, how can one glean the benefits of fish but stave off the detriments of mercury? Partake in moderation and know your fish. The American Heart Association now advises eating two servings of low-mercury fish per week. Wild-caught salmon is very low in mercury — and low in PCBs that can contaminate farmed salmon — as is freshwater trout. Tilapia, herring, sardines, catfish and flounder (sole) are also good, low-mercury choices. Chunk light tuna is a better selection than albacore, with a third of the mercury on average. A general guideline is to choose fish with mercury levels well below the FDA recommendation of one part per million. Though eating fish may not give you infinite knowledge or make all your wishes come true, consuming it sensibly will set you on the path to a healthier, longer life.

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