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:footnote 1
- Do not eat shark, swordfish, king mackerel, marlin, orange roughy, bigeye tuna, or tilefish from the Gulf of Mexico, because these all contain high levels of mercury.
- Women who may become pregnant, pregnant women, nursing mothers, and children older than 10 years, should eat between 8 oz (227 g) and 12 oz (340 g) a week (2 or 3 average meals) of a variety of fish and shellfish that are lower in mercury. Children ages 10 and younger should eat less.
- 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 2 or 3 meals of fish and shellfish, you may eat up to 4 oz (113 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 4 oz (113 g) a week (one average meal) of fish caught from local waters, but don't eat any other fish during that week.
Should a woman who is not planning a pregnancy be concerned?
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.
Where can you get more information?
For specific information on:
- The amount of mercury in commercial fish, see www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm115644.htm.
- The fish or shellfish caught by family and friends in your local lakes, rivers, and coastal areas, see www.epa.gov/choose-fish-and-shellfish-wisely/fish-and-shellfish-advisories-and-safe-eating-guidelines#tabs-4.
For general information on mercury in fish, see:
- Your local health department or environmental agency.
- The EPA mercury website at www.epa.gov/mercury/exposure.htm.
- The FDA seafood website at www.fda.gov/food/guidanceregulation/guidancedocumentsregulatoryinformation/seafood/ucm2006751.htm.
- U.S. Food and Drug Administration and U.S. Environmental Protection Agency (2017). Eating fish: What pregnant women and parents should know. U.S. Food and Drug Administration and U.S. Environmental Protection Agency. www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm393070.htm. Accessed April 3, 2017.
Current as of: February 11, 2020
Author: Healthwise Staff
Sarah Marshall MD - Family Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine
Elizabeth T. Russo MD - Internal Medicine
Kirtly Jones MD - Obstetrics and Gynecology
Current as of: February 11, 2020