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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.
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
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:
If you are concerned about your or your child's mercury
level, talk to your doctor or local health department about testing.
The FDA and EPA recommend that women who may
become pregnant, pregnant women, nursing mothers, and young children:1, 2
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.
Mercury accumulates in your bloodstream over time and
slowly leaves the body through urine, feces, and breast milk. If you eat a lot
of fish high in mercury, it may take up to a year for your mercury levels to
drop after you stop eating the fish. If you decide to become pregnant or if you have
an unplanned pregnancy, you may have high levels of mercury. While elevated
levels of mercury usually do not cause significant health problems, they may
affect a developing
fetus. If you are of childbearing age, try to follow
the guidelines above when you eat fish.
For general information on mercury in fish, see:
U.S. Food and Drug Administration (2004). What you
need to know about mercury in fish and shellfish: 2004 EPA and FDA advice for
women who might become pregnant, women who are pregnant, nursing mothers, young
children. Available online:
U.S. Department of Health and Human Services, U.S. Environmental Protection Agency (2011). Mercury Levels in Commercial Fish and Shellfish. Available online: http://www.fda.gov/Food/FoodSafety/Product-SpecificInformation/Seafood/FoodbornePathogensContaminants/Methylmercury/ucm115644.htm.
Current as of:
June 4, 2014
Sarah Marshall, MD - Family Medicine & Siobhan M. Dolan, MD, MPH - Reproductive Genetics
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