After I recently caught myself on my third order of yellowtail and salmon sashimi of the week, I started to think about the warnings I've read about high mercury levels in fish.
After I recently caught myself on my third order of yellowtail and salmon sashimi of the week, I started to think about the warnings I've read about high mercury levels in fish. I wondered: Could my newfound sushi obsession put me at risk for mercury poisoning?
To learn more, I reached out to Navya Mysore, M.D, a primary-care physician specializing in women’s health at One Medical. Turns out, I don’t need to be overly concerned about full-blown mercury poisoning from seafood. However, I learned that less-severe mercury toxicity is no joke either-and it is important to know which types of fish can raise your risk.
For those of us who weren't chem majors, mercury (a.k.a. quicksilver or Hg on the periodic table) is a heavy metal that’s naturally found in the earth’s crust, Mysore explains. There are three forms of the metal: elemental, inorganic, and organic.
Mercury in its organic form isn't dangerous, she says. The trouble arises when it is broken down by bacteria into methylmercury-the dangerous, dietary form of mercury. This is what’s found in certain kinds of fish and shellfish. Generally, larger fish-like shark and swordfish-are higher in mercury, because they live longer and are higher on the food chain, says Jagdish Khubchandani, Ph.D., a professor of community health at Ball State University.
Another less common source of exposure is to elemental mercury, which occurs through inhaling vaporized mercury, not eating fish. Those whose work includes coal mining or working in a factory that manufactures products containing mercury (i.e. thermometers, barometers, dental fillings), but the majority of people aren’t at risk of that type of exposure, Mysore says.
Acute cases are rare, but mercury toxicity isn't exactly unheard of: It’s estimated that high levels of mercury in blood can be found in 5 to 10 percent of Americans, says Khubchandani.
This can be the result of low-grade yet chronic exposure to methylmercury in fish, which can build up over time and cause some serious health issues, Mysore says.
Here’s how long-term exposure can play out in your body.
1. Developmental delays in babies: Methylmercury is particularly harmful to fetuses, Mysore says, which is why pregnant women need to be cautious about what types of fish they eat. (More on that below.) Even though the mother may not experience symptoms of toxicity, her baby may have brain damage due to high exposure to mercury, Khubchandani says. This can lead to problems with behavior, cognition, attention span, and motor activity later in life.
2. Cognitive issues: People with high levels of mercury may experience trouble thinking, memory problems, and they may be more irritable, Mysore says.
3. Impaired motor skills: This can include tremors (uncontrollable shaking), lack of coordination or inability to walk, muscle weakness, and numbness or “pins and needles” sensations, Khubchandani says.
4. Shortness of breath: Because of toxicity in the lungs, you may experience shortness of breath or trouble breathing, Mysore says.
5. Neurological symptoms: Exposure to elemental mercury (again, by inhaling the vapor, not eating fish), can affect brain and nervous system function, causing headaches, insomnia, dizziness, and poor cognitive function, says Khubchandani. Seizures may also occur. Blindness and double vision are also possible.
6. Oral issues: If inhaled or swallowed, elemental mercury can cause a metallic taste in the mouth, or swollen bleeding gums.
7. Organ failure: In severe cases, elemental mercury poisoning may result in systemic organ failure, which can lead to death, Khubchandani notes.
Since the symptoms above are all fairly non-specific symptoms, check in with your primary-care physician if you’re concerned, and tell them what you’ve been eating, Mysore says. They can perform simple blood tests to determine your mercury levels.
The good news: you don’t need to avoid fish or give up your sushi habit entirely. Most kinds of fish are good sources of protein, vitamins, and minerals, says Khubchandani, and the nutritional benefits outweigh the risks.
The FDA recommends two to three servings of fish per week, as well as varying the types of fish you eat-especially if you exceed three servings. Mysore takes it a step further and recommends spacing fish dishes out to at least every other day. And cut your intake of fish that are highest in mercury: Tilefish, swordfish, shark, king mackerel, and tuna top the FDA’s most recent list.
Other ways you can reduce mercury levels in your body include drinking plenty of water; making sure that you have regular bowel movements to keep things moving; increasing your dietary vitamin C levels (through leafy greens and citrus fruits); and taking a probiotic supplement.
A final (and important) note: If you’re pregnant, check out this helpful chart by the FDA and EPA to choose which fish to eat, how much and how often, and which fish you should avoid.