Nevadans should include fish in their diet twice a week, although pregnant women, nursing mothers and small children should avoid certain types of locally caught and commercially distributed marine fish that have high mercury concentrations, researchers from the University of Nevada, Reno say.
The key, according to one of the researchers, nutritionist Kerry Seymour of University of Nevada Cooperative Extension (UNCE), is to eat fish that are high in beneficial Omega-3 fatty acid and low in mercury contamination – such as salmon and trout.
“People get confusing advice sometimes,” Seymour said. “Some fish are high in mercury and do need to be avoided. But fish is a good source of low-fat protein, and people should have it as a regular part of their diet. It’s about choosing the right type of fish to eat.”
Seymour worked with UNCE water quality specialist Sue Donaldson, Natural Resources and Environmental Science professor Mae Gustin and graduate student Melissa Markee on the two-year study, which examined the sources of mercury in Nevada, its concentration in various state reservoirs, and the fish-eating eating habits of Nevadans.
Some of their findings:
- Mercury is a worldwide issue, and contamination at any given site could just as easily come from another hemisphere as a local source. That’s because mercury is released into the atmosphere and can circulate around the globe before being deposited in a distant locale. That atom of mercury found in a Nevada fish could have come from China, Gustin said.
- About a third of the mercury circulating around the globe comes from human sources – such as coal-fired power plants – and nearly half of that amount comes from China. The United States contributes about 9 percent of the human-caused mercury sources, Donaldson said.
- The risks from mercury were vividly illustrated in the 1950s at Minamata Bay in Japan, where local residents eating mercury-tainted fish suffered birth defects. The mercury was traced to discharges from the Chisso chemical factory along the cost of the Shiranui Sea.
- Mercury is also released into the environment from natural sources, including volcanoes, geothermal fields and the natural weathering of cinnabar, an ore that contains mercury.
- Mercury is converted to methyl mercury through sulfate-reducing bacteria, and this is the form found in fish. Fish accumulate mercury in their flesh, making fish consumption the major pathway to humans.
- Larger, older and more predatory fish (those that eat other fish) tend to have higher concentrations of mercury and should be avoided. These fish include shark, swordfish, king mackerel and tilefish.
People shouldn’t eat fish from Lahontan Reservoir and the Carson River below Dayton, and should avoid eating certain fish in other reservoirs, including Rye Patch (walleye and wiper); Chimney Dam Reservoir (walleye); Big and Little Washoe lakes (white bass); and Comins Lake (Northern pike and largemouth bass). Also, because of the level of mercury contamination, carp taken from the Washoe lakes shouldn’t be eaten more than once a month; carp and white crappie from Chimney Dam shouldn’t be eaten more than once a month, and rainbow trout from Comins should be limited to once a month. Yellow perch from Chimney Dam can be eaten twice a month and white crappie, yellow perch, green sunfish and brown bullheads from Rye Patch can be eaten up to four times a month.
A survey of nearly 2,000 Nevada anglers and more than 500 members of the general population revealed that only 6 percent of the anglers eat fish twice a week as recommended by nutritionists while 11 percent of the general population eat fish twice a week. Anglers generally avoided fish, such as walleye, that have advisories against eating them. But a small percentage of anglers were consuming these fish often enough to pose a health risk, Seymour said.
You don’t have to eat a lot of fish to get the benefits; a 3-ounce cooked filet, about the size of a deck of cards, eaten twice a week is recommended.
There is strong evidence that the fat in fish is essential for healthy brain and eye development in infants and young children, Seymour said. It’s especially important for women who are pregnant, may become pregnant or are breastfeeding to eat two 3-ounce meals of a variety of cooked fish per week. Shark, swordfish, tilefish, king mackerel, any raw fish and more than 12 ounces of albacore white tuna should be avoided.
In adults, eating fish has been shown to decrease the risk of heart disease and stroke, and improve a person’s blood lipid profile. Other benefits may include: lower blood pressure, improvements in depression and rheumatoid arthritis, and lowered risk of macular degeneration and type 2 diabetes.
FOR MORE INFORMATION:
The two-year University of Nevada, Reno study of mercury in fish led to the publication of two fact sheets: Eating Fish: Making Healthy Choices, which was written for pregnant and nursing mothers, and Mercury in Fish: Information for Health Professionals, which was designed to help doctors communicate with their patients about fish consumption.
The fact sheets were written by University of Nevada Cooperative Extension Nutrition Specialist Kerry Seymour and Water Quality Education Specialist Susan Donaldson, and are available on the Cooperative Extension Website.
Researchers will release more details about their study in upcoming articles in professional journals.