Does mercury contamination outweigh the health benefits of eating fish?

The risk of getting too much mercury or other contaminants from fish is generally outweighed by the health benefits that omega-3 fatty acids have. The main types of toxins in fish are mercury, dioxins and polychlorinated biphenyls (PCBs). The amount of toxins depends on the type of fish and where it's caught.

Mercury occurs naturally in small amounts in the environment. But industrial pollution can produce mercury that accumulates in lakes, rivers and oceans, which turns up in the food fish eat. When fish eat this food, mercury builds up in the bodies of the fish.

Large fish that are higher in the food chain — such as shark, tilefish, swordfish and king mackerel — tend to have higher levels of mercury than do smaller fish. Larger fish eat the smaller fish, gaining higher concentrations of the toxin. The longer a fish lives, the larger it grows and the more mercury it can collect.

Pay attention to the type of fish you eat, how much you eat and other information such as state advisories. Each state issues advisories regarding the safe amount of locally caught fish that can be consumed.

Should anyone avoid eating fish because of the concerns over mercury or other contaminants?

If you eat enough fish containing mercury, the toxin can accumulate in your body. It can take as long as a year or more for your body to remove these toxins. Mercury is particularly harmful to the development of the brain and nervous system of unborn children and young children. For most adults, however, it's unlikely that mercury would cause any health concerns.

Still, the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) recommend that these groups limit the amount of fish they eat:

  • Women who are pregnant or trying to become pregnant
  • Breast-feeding mothers
  • Young children

Pregnant women, breast-feeding mothers and children can still get the heart-healthy benefits of fish by eating fish that's typically low in mercury, such as salmon, and limiting the amount they eat to:

  • No more than 12 ounces (340 grams) of fish in total a week
  • No more than 6 ounces (170 grams) of canned tuna a week
  • No amount of any fish that's typically high in mercury (shark, swordfish, king mackerel and tilefish)

Are there any other concerns related to eating fish?

Several recent studies have linked high levels of omega-3 fatty acids in the blood to an increased risk of prostate cancer. But, these studies weren't conclusive, and more research needs to be done to confirm this link. Talk with your doctor about what this potential risk might mean to you.

Can you get the same heart-health benefits by eating other foods that contain omega-3 fatty acids, or by taking omega-3 fatty acid supplements?

Eating fish rich in omega-3 fatty acids and other nutrients appears to provide more heart-healthy benefits than does using supplements. Other nonfish food options that do contain some omega-3 fatty acids include flaxseed, flaxseed oil, walnuts, canola oil, soybeans and soybean oil. However, similar to supplements, the evidence of heart-healthy benefits from eating these foods isn't as strong as it is from eating fish.

Feb. 07, 2014 See more In-depth