Fish can be a very healthy food and provide a high-quality source of dietary protein. However, some fish can also serve up a portion of a dangerous substance.
Mercury found in some fish and shellfish can cause harm to an unborn baby or a child’s developing nervous system.
The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) have both created guidelines for consuming certain fish and shellfish known to contain mercury.
Specific guidelines apply to pregnant women so that they can get the health benefits of eating fish, but decrease the risks associated with eating fish containing mercury.
How does mercury get into fish?
Mercury occurs naturally in nature. It can also be released into the air from coal burning, metal mining and industrial pollution. Mercury released into the air through pollution accumulates in the soil and water.
In water, it is turned into methylmercury — the form of mercury that is dangerous to young children and unborn babies.
Fish absorb methylmercury from the water, and it is stored in their bodies. Methylmercury builds up in certain types of fish and shellfish more than others.
The amount of methylmercury in fish depends on how big they are, how long they live and how much mercury is in the fish they eat.
Which fish may have mercury?
Mercury has been found in all five of the Great Lakes and in waterways in all 50 states. The National Resources Defense Council has estimated that 43 percent of all the wetlands in the US are polluted with mercury.
If you don't know where the fish you plan to eat was caught, consider these general rules of thumb:
- High mercury levels are often found in shark, swordfish, king mackerel and tilefish from the Gulf of Mexico.
- Low mercury levels are found in shrimp, canned light tuna, salmon, pollock, tilapia, cod and catfish.
Deborah Gordon, MD, a homeopathic and nutrition expert, told dailyRx News, "Fish is a healthy food because of the protein source and, for ocean fish, because of the high omega-3 content. I encourage everyone to work fish into their diet, and where possible to rely on fish from cold water parts of the ocean, such as fresh wild Pacific salmon or halibut, and canned wild salmon, anchovies, sardines, mackerel and herring.
"Oceans and almost all ocean fish are rich in selenium, which performs the incredibly useful task of binding with mercury inside our digestive tracts and actually escorting the mercury out of our bodies, thereby preventing its absorption," she continued.
Dr. Gordon's advised, "Freshwater fish demonstrate variable levels of both selenium and mercury, so it is not as predictably safe as fish caught wild in the ocean, and is therefore safer as an occasional meal rather than a regular one."
Recommendations for pregnant women and children
The FDA recommends that pregnant and breastfeeding women and young children only consume fish from the list of those containing low levels of mercury.
The recommendations include eating 8 to 12 ounces of a variety of fish per week and limiting albacore, or white tuna, to 6 ounces a week.
The FDA recommends 2 or 3 servings of fish a week for young children, with the reminder that smaller children should be served smaller portion sizes than adults.
When eating fish caught by people fishing waterways, the FDA recommends paying attention to fish advisories on those water bodies. When no advisory is available, portions should be limited to 6 ounces a week. Young children can eat 1 to 3 ounces of fish caught from these sources weekly, but no other fish should be eaten that week.
Risks and facts of mercury poisoning
The human body does not need mercury, and there should be no mercury in a person’s body, blood or urine.
Amounts found in the blood, urine or tissue mean that a person has been exposed, usually by eating methylmercury. High levels of mercury in the body can indicate methylmercury poisoning.
Mercury affects a child or unborn baby’s developing nervous system and growing brain. Exposure to methylmercury in unborn babies can affect thinking, memory, language, attention, fine motor skills and visual skills.
In adults, mercury exposure can affect the nervous, immune and digestive systems, as well as the lungs, kidneys, skin and eyes.
The following symptoms may be present in cases of methylmercury poisoning. If you experience these symptoms, see a doctor immediately:
- Feelings of pins and needles in the hands, feet or around the mouth
- Uncoordinated movements, lack of balance or difficulty walking
- Effects on vision at the edges of the field of vision (effects on peripheral vision)
- Effects on speech or hearing
- Muscle weakness