The Medical Minute: Something fishy about seafood?

March 24, 2004

Clearing up conflicting reports about whether fish are good for your health
By John Messmer, M.D.
Penn State Milton S. Hershey Medical Center

How about fish for dinner? When you travel to the beach, you probably go out for fresh seafood a few times while you're there. Fish is a good choice, right? After all, physicians and other healthcare experts say we should eat less red meat and more fish. Fish is low in fat, and its fat is polyunsaturated, which is good for our cholesterol. Fish also has omega-3 fatty acids that help keep our arteries clean and can reduce the risk of heart disease. Some experts think we can cut our risk of heart disease in half by eating two fish dinners a week. It's a good source of protein, too.

But you might question the consumption of seafood with reports from the Environmental Protection Agency (EPA) about the dangers associated with eating fish. These seemingly contradictory recommendations can make it difficult to sort the risk from the benefit.

Here's the problem: chemicals from the air and land eventually get into the water in our streams, lakes and oceans. Pesticides from farms, mercury in smoke and fly ash from factories, dioxins from the paper industry and forest fires, and toxic metals from landfills eventually flow into the water where they settle to the sediment. Plants, microscopic animals and microorganisms ingest the toxic substances and concentrate them. Fish feed on plants and organisms in the water and store the contaminants in their flesh and fat. Since the toxins take a long time to be eliminated, they tend to concentrate further in the fish. When we consume the fish, we then absorb whatever toxins the fish have stored.

Probably the biggest concern now is mercury. Chronic high blood levels of mercury damage the nervous system and kidneys causing tremors, fatigue, weight loss, irritability, incoordination, memory loss and intellectual deterioration. Severe toxicity impairs hearing, swallowing, and can cause death. Children and fetuses, because of their developing nervous systems are particularly susceptible.

In the past, mercury poisoning was a hazard of the mirror and felt hat industry. The "mad hatter" in "Alice in Wonderland" was interpreted to be a victim of mercury poisoning. In the 1950s, Minamata, Japan was the site of the tragic poisoning of more than 100 people from fish heavily contaminated with mercury. Mercury levels in the Minamata fish exceeded 50 parts per million (ppm -- one part per million is one milligram of mercury in one kilogram of fish). The most heavily contaminated fish commercially available now have less than one ppm mercury.

Mercury enters the environment from industrial pollution and from many other more mundane sources. Switches, dental amalgam, fluorescent lights, thermometers and thermostats also contribute to the contamination. Ideally these items should be recycled but finding a mercury recycler can be tricky. In most states, you can check with the environmental protection department. In Pennsylvania, visit http://www.dep.state.pa.us/dep/deputate/airwaste/wm/HHW/Facts/Events.htm... to see the 2004 collection events for household hazardous waste.

So, how about that fish dinner? If fish is a major part of your diet as it can be in Asian cuisine, you should be aware of the species with the highest concentrations of mercury: bowfin, pickerel, largemouth bass, walleye, spotted bass, pike, king mackerel, shark, tilefish, bluefish, croaker, swordfish and some salmon. Larger fish have lived longer and have had more time to consume and store mercury so the safe amounts are lower for them.

Although the average American ate 15 pounds of seafood in 2002, that's only a little less than 5 ounces a week. Current recommendations are based on a meal consisting of 6 ounces of fish (8 ounces before cooking). Adult men and non-nursing women who will not become pregnant can usually have three-to-four meals per month of blue-fin and yellow-fin tuna, lobster, perch, catfish, trout and smelt; two-to-three meals per month of canned tuna, grouper, oysters, bass and sunfish; two meals per month of orange roughy, croaker, and one or two meals per month of salmon, bowfin and pickerel although recommendations vary slightly among environmental agencies.

Children, nursing mothers and pregnant women should have the fish mentioned above about half as frequently or in half the quantity as everyone else. Children, nursing mothers and pregnant women also should not eat king mackerel, shark, swordfish, tilefish, striped bass, eel and bluefish and adult men and non-pregnant women should eat them rarely if at all. For sport fishers, check your state's environmental protection and game management departments for current recommendations according to species and stream.

For recommendations on amount and frequency for various fish, visit http://www.epa.gov/waterscience/fishadvice/1-meal-per-week.pdf or http://www.environmentaldefense.org/seafood/fishhome.cfm to search by fish species.

So, go ahead and have some fish. Prepared fish patties, fish sticks and light tuna are very low in mercury. Most species of fresh fish are fine. And remember there is also a health benefit from fish and most authorities agree the benefit outweighs the risk if good judgment is used.

(Media Contacts)

Last Updated March 19, 2009