What To Know About Mercury In Fish

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Mercury, a naturally occurring but potentially harmful element, can become concentrated in aquatic food chains, making its presence in fish a public health concern. Regular fish consumption is highly recommended due to the abundance of essential nutrients like omega-3 fatty acids and iron found in some types of seafood. However, the presence of mercury in fish can pose serious health risks, especially for certain populations, including children and pregnant people.

Understanding the potential effects of mercury on your health, the mercury content in different types of fish, safe consumption limits and who should avoid eating fish high in mercury can help you make informed choices about your seafood consumption. Read on to learn more about mercury in fish and how to enjoy seafood safely.

What Is Mercury?

Mercury is a naturally occurring element which can be released into the environment through both natural processes, such as volcanic eruptions and forest fires, and human activities such as the burning of coal, oil or wood as fuel. Once mercury is released into the air, it can fall to the ground in raindrops, snowflakes, dust or due to gravity and contaminate the soil or water.

When mercury enters water sources, such as lakes, oceans and rivers, it undergoes a process known as methylation, where certain microorganisms in the water convert the mercury to a form called methylmercury.

“The methylmercury is absorbed through the gills of fish but also accumulates as fish eat smaller fish,” explains Jordyn Wallerius, a registered nutritionist and certified dietitian for Nutrisense, a data-based  online health-coaching platform. “As a result, mercury becomes more concentrated as it moves up the food chain. Larger fish that live longer, such as swordfish, shark and certain kinds of tuna, tend to be highest in mercury.”

What Does Mercury Do to Your Health?

“Although regular consumption of fish can provide many health benefits, it’s also important to consider that fish can be higher in mercury and that there are some significant health concerns that potentially come along with this,” says Wallerius.

Consuming higher levels of mercury can lead to serious health problems, particularly affecting the brain and nervous system, including:

  • Tingling or numbness in mouth, hands or feet
  • Vision and hearing impairment
  • Loss of peripheral vision
  • Muscle weakness and inability to coordinate movement

In pregnant and breastfeeding individuals, mercury exposure can also affect the development of the baby’s brain and nervous system, leading to impaired cognitive thinking, memory, attention, language, fine motor skills and visual spatial skills.

Fish High in Mercury

Mercury levels in fish vary depending on the type of fish, where they were caught and how high up they are on the food chain. Generally, larger and longer-living predatory fish tend to have higher mercury levels compared to smaller, shorter-lived species, explains Amy Fox, a certified nutritionist and founder of Food and Mood Lab, an online nutrition education and coaching platform.

According to the U.S. Food and Drug Administration (FDA), fish high in mercury include:

  • King mackerel
  • Marlin
  • Orange roughy
  • Shark
  • Swordfish
  • Tilefish
  • Bigeye tuna

Low-Mercury Fish

Despite the concerns about mercury, fish is still considered an important part of a healthy diet. There are many types of low-mercury fish that can be safely consumed on a regular basis, says Fox.

According to the FDA, the best choices for low-mercury fish include:

  • Anchovy
  • Atlantic croaker
  • Atlantic mackerel
  • Black sea bass
  • Butterfish
  • Catfish
  • Clam
  • Cod
  • Crab
  • Crawfish
  • Flounder
  • Haddock
  • Hake
  • Herring
  • Lobster, American and spiny
  • Mullet
  • Oyster
  • Pacific chub mackerel
  • Perch, freshwater and ocean
  • Pickerel
  • Plaice
  • Pollock
  • Salmon
  • Sardine
  • Scallop
  • Shad
  • Shrimp
  • Skate
  • Smelt
  • Sole
  • Squid
  • Tilapia
  • Trout, freshwater
  • Tuna, canned light (includes skipjack)
  • Whitefish
  • Whiting

Should You Avoid Eating High-Mercury Fish?

For most healthy adults and children at least 6 years old, fish high in mercury should be limited to no more than once per week. However, the FDA and Environmental Protection Agency (EPA) advise that young children, as well as pregnant and breastfeeding people, completely avoid fish high in mercury. Other populations, such as elderly people and those with a weakened immune system, should also avoid eating high-mercury fish.

“While fish that are high in mercury may also be high in nutrients that are difficult for us to get from other sources, the risk can potentially be higher than the reward for some people,” says Wallerius, who adds, “instead, these groups of people should lean toward consuming lower- mercury fish options.”

Benefits of Eating Fish

While too much mercury in fish is a health concern, experts recommend eating fish in moderation as part of a healthy diet. The benefits of eating fish as part of a healthy and balanced diet include:

  • Omega 3 fatty acids found in fish may protect against heart disease
  • Consuming fish during pregnancy and while breastfeeding may help with a baby’s brain and nervous system development
  • Decreases in the risk of colon and rectal cancers
  • Decreased risk of becoming obese
  • Better bone health

Mercury in Fish: How Much Is Too Much?

The Dietary Guidelines for Americans recommends regularly eating fish as part of a healthy diet. However, individuals who are more susceptible to the effects of mercury should avoid fish high in mercury and instead consume a variety of fish that are low in mercury.

The FDA and EPA offer the following recommendations:

  • Individuals who are pregnant or breastfeeding: Two or three (4 ounce) servings of fish low in mercury per week.
  • Children ages 1 to 3 years old: Two (1 ounce) servings of fish low in mercury per week.
  • Children ages 4 to 7 years old: Two (2 ounce) servings of fish low in mercury per week.
  • Children ages 8 to 10 years old: Two (3 ounce) servings of fish low in mercury per week.
  • Children ages 11 years and older: Two (4 ounce) servings of fish low in mercury per week.

Mercury Risk

“Eating seafood and most types of fish is relatively safe for most people and considered part of a healthy diet,” says Fox. “However, certain groups of people may be more susceptible to the effects of mercury than others.” warns Fox. These include:

  • People who are pregnant or might become pregnant
  • Breastfeeding individuals
  • Children
  • Elderly people
  • Individuals with a weakened immune system
  • People with chronic exposure to high levels of mercury, including those who are exposed at work or populations who rely on fishing, such as Brazil, Canada and China

If you fall into one of these groups, it’s especially important to pay attention to the mercury levels in fish and avoid consuming fish that contain higher levels of mercury, Fox adds.

When to Call a Doctor

“Potential symptoms [of mercury toxicity] to watch out for may include difficulty breathing, nausea or vomiting, diarrhea, feeling numbness in your body, double/blurred vision or even seizures,” says Wallerius, who advises that anyone who is concerned about mercury exposure or experiencing symptoms associated with high levels of mercury seek medical attention immediately.

“Mercury in fish is a topic that should not be ignored, but it’s important to remember the health benefits that come with eating fish in moderation,” adds Fox. “By following safe consumption recommendations and being aware of the fish that contain high levels of mercury, you can enjoy the benefits of this healthy food while minimizing the risks.”