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What is mercury?

Mercury is a metal found naturally in the environment. Human activities, such as farming, burning coal, and using mercury in manufacturing, increase the mercury cycling through the air, water, and soil. In water, mercury changes its form and becomes methylmercury. Fish absorb this mercury. When you eat fish containing mercury, you absorb the mercury, and at high levels it can be harmful. Mercury will leave the body over time in the urine, feces, and breast milk.

Do you need to avoid the mercury found in fish?

For most people, the level of mercury absorbed by eating fish and shellfish is not a health concern. Overall, fish and shellfish are healthy foods. They contain high-quality protein and other essential nutrients, are low in saturated fat, and contain omega-3 fatty acids, a type of essential fatty acid. A balanced diet that includes fish and shellfish can contribute to heart health and children's growth and development.

Nearly all fish and shellfish contain traces of mercury. But some contain high levels. Eating large amounts of these fish and shellfish can result in high levels of mercury in the human body. In a fetus or young child, this can damage the brain and nerves (nervous system).

Because of the mercury found in fish, the U.S. Food and Drug Administration (FDA) and U.S. Environmental Protection Agency (EPA) advise the following people to avoid eating fish high in mercury and to eat limited amounts of fish and shellfish that are lower in mercury:

  • Women who may become pregnant
  • Pregnant women
  • Nursing mothers
  • Young children

If you are concerned about your or your child's mercury level, talk to your doctor or local health department about testing.

How should you change your eating habits to reduce your exposure to mercury in fish?

The FDA and EPA recommend that women who may become pregnant, pregnant women, nursing mothers, and young children:1, 2

  • Do not eat shark, swordfish, king mackerel, or tilefish, because these all contain high levels of mercury.
  • Eat up to 12 oz (340 g) a week (two average meals) of a variety of fish and shellfish that are lower in mercury.
    • Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.
    • Another commonly eaten fish, albacore ("white") tuna, has more mercury than canned light tuna. So when choosing your two meals of fish and shellfish, you may eat up to 6 oz (170 g) a week (one average meal) of albacore tuna.

Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 oz (170 g) a week (one average meal) of fish caught from local waters, but don't eat any other fish during that week.

WebMD Medical Reference from Healthwise

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