While fish is an important component of an anti-aging diet—thanks to the high-quality protein and heart-healthy omega-3 fatty acids in many species—people often question whether it’s safe to eat fish and shellfish, given the dangers of mercury exposure. Here's a look at what mercury poisoning is, and how to avoid it in the fish you eat.
How are we exposed to mercury? Mercury is a poisonous metal used in some manufacturing and industrial processes. There are different kinds of mercury, but the type we're exposed to when we eat contaminated fish is an organic form called methylmercury. Methylmercury is created by microorganisms when mercury in the air falls into lakes and streams. Fish living in these bodies of water absorb the methylmercury in their tissues to varying degrees. They also absorb methylmercury by eating other contaminated fish.
Past wide-scale mercury poisonings from industrial pollution have occurred in cities like Minamata, Japan, giving rise to what is now known as Minamata disease.
Effects of methylmercury on humans: The dangers associated with methylmercury depend on how much is in the fish we eat, how often we eat it, and how old we are.
According to the US Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA), the risks of trace amounts of methylmercury from fish are not usually a health concern for people beyond childbearing age. But methylmercury is dangerous for unborn fetuses and infants, as it acts on the developing central nervous system: the brain and spinal cord. According to the US National Institutes of Health, many of the neurological symptoms caused by methylmercury poisoning are similar to symptoms of cerebral palsy.
- Growth problems
- Brain damage
- Damage to kidneys and liver
Prevent mercury poisoning: Damage from these toxic compounds cannot be reversed. The best way to prevent mercury and methylmercury poisoning is to avoid the types of fish that contain the greatest amounts. These include large, predatory fish species that accumulate methylmercury in their tissues over time: shark, swordfish, tilefish and marlin.
Methylmercury collects in the human bloodstream. While it's eliminated naturally by the body, this process can take a matter of several months. That’s why both the US Food and Drug Administration and the Environmental Protection Agency recommend that women who are pregnant, hope to become pregnant, or those who are nursing avoid fish with the highest levels altogether. Health Canada recommends other consumers limit their consumption of these large species to no more than one meal per week.
For consumers of all ages, government recommendations in Canada and the US suggest choosing fish and shellfish with lower levels of mercury—including canned light tuna, salmon, sole and shrimp—up to twice a week.
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Mercury: Health Effects. US Environmental Protection Agency Public Information Sheet. Accessed September 24, 2012.
Mercury: Your Health and the Environment. Health Canada Public Information Sheet. Accessed September 24, 2012.
Methylmercury Poisoning. US National Institutes of Health Medline Public Information Sheet. Accessed September 24, 2012.
What You Need to Know About Mercury in Fish and Shellfish. US Food and Drug Administration Public Information Sheet. Accessed September 24, 2012.