Omega-3s, Fish, and Mercury in the Diet

You've heard you should eat more fish because it's good for your heart. But you may also be concerned about mercury and other contaminants. What is a health-conscious consumer to do? Here's the low-down on fish: how much to eat, how to avoid mercury and other toxins, and whether you should take a fish oil supplement.

Salmon with citrus and vegetables
Davide Illini / Stocksy United

Fish for Heart Health

Oily or "fatty" fish, such as salmon, tuna, and sardines, are an excellent source of heart-healthy omega-3 fatty acids. Though some studies to date have been inconclusive on the heart-health benefits of omega-3s, a 2019 meta-analysis of the largest trials to date found omega-3 supplements reduce the risk of cardiovascular disease, with greater benefits at higher doses (over 840 mg a day). Though the analysis did not find a benefit for stroke, omega-3 supplements reduced the risk of heart attack, as well as hospitalization or death for cardiovascular reasons, in more than 120,000 people included in 13 trials. Omega-3s help the heart, other research suggests, because they may reduce inflammation and slow plaque buildup in the arteries.

Is an Omega-3 Supplement as Good as Fish?

Omega-3s are a unique form of nutrient known as "essential," meaning that you must obtain them from food or a supplement pill. Your body cannot make the nutrient from other fats, carbohydrates, or proteins. Omega-3s are not very common in the foods we eat and are mostly found in fish, seafood, and some plant sources.

If you don't enjoy fish, you can opt for a supplement. While it's generally best to get nutrients from food, it's better to get fish oil in your diet than not. If that means taking a supplement, go for it (but consult your healthcare provider first). Current research indicates they are as good for you as food sources.

How Much Omega-3 Do You Need?

The American Heart Association recommends eating fish twice a week, while the FDA recommends two to three servings of fish per week. If you're taking a supplement or getting omega-3s through fortified foods, then shoot for 250 to 500 mg a day. (Note, too, that 1,000 mg of fish oil is not equivalent to 1,000 mg of combined EPA and DHA—check labels to see how much omega-3 your supplement actually contains.) Consult your healthcare provider before starting this or any other supplement. Some medications, including blood pressure medications such as beta-blockers, blood thinners, and diuretics, could interact with fish oil.

Beyond fish and fish oil, there are plant-based forms of omega-3s. For example, a handful of walnuts, a tablespoon of canola oil over salad or a tablespoon of ground flaxseed over your breakfast cereal are all good ways to get omega-3s in your diet.

Mercury in Fish

Mercury is a naturally occurring element, but it is also a byproduct of pollution. In high amounts, ingesting mercury can cause neurological problems. All fish and seafood contain some amount of mercury. So while it is impossible to avoid mercury entirely when eating fish and seafood, you can make lower-mercury choices. Experts recommend avoiding fish with the highest levels of mercury and eating low-mercury fish and other seafood. For children, or if you're a woman who's pregnant or nursing or could become pregnant, these recommendations are even more important.

Examples of Low-Mercury Seafood High-Mercury Fish to Avoid
Salmon, flounder, pollock, shrimp, clams, scallops, and crab King mackerel, shark, swordfish, orange roughy, marlin, bigeye tuna, and tilefish
Sardines, canned light tuna, and anchovies Albacore tuna has more mercury than light tuna.

As with other animal foods, seafood can also have additional contaminants (such as dioxins and polychlorinated biphenyls, or PCBs). However, nutrition researchers agree that the benefit of eating fish and seafood far outweighs any potential risk of PCBs you may consume.

Eating Fish During Pregnancy

While eating low-mercury fish is healthy for everyone, the EPA and FDA suggest it’s particularly good for three groups of people: pregnant and breastfeeding women, women who might become pregnant, and young children. Their combined recommendations suggest women who are pregnant or breastfeeding eat between 8-12 ounces of low-mercury fish each week. Children between ages 2 and 11 should have fish once or twice a week in portions of 1 to 4 ounces depending on their age. Moms may be happy to hear that fish sticks count!

Wild vs. Farmed Salmon

There is considerable controversy about wild versus farmed fish, especially salmon. Wild fish advocates state that wild fish, such as wild Atlantic salmon, have fewer PCB contaminates than their farmed counterparts. Proponents of farmed fish, especially farmed Pacific salmon, note that farmed fish have as much and sometimes more DHA and EPA omega-3s than wild salmon.

As a consumer, it is important to know that even these claims may change as farmed and wild fish purveyors change their methods of feeding and collection to meet consumer demand. Ultimately, the benefits of both farmed and wild fish outweigh the risks when it comes to protecting your health.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Hu Y, Hu FB, Manson JE. Marine Omega-3 Supplementation and Cardiovascular Disease: An Updated Meta-Analysis of 13 Randomized Controlled Trials Involving 127,477 Participants. J Am Heart Assoc. 2019;8(19):e013543. doi:10.1161/JAHA.119.013543

  2. Bäck M. Omega-3 fatty acids in atherosclerosis and coronary artery disease. Future Sci OA. 2017;3(4):FSO236. doi:10.4155/fsoa-2017-0067

  3. National Institutes of Health. Omega-3 Fatty Acids.

  4. United States Environmental Protection Agency. EPA-FDA Advice about Eating Fish and Shellfish.

  5. Harvard University, T.H. Chan School of Public Health. Fish: Friend or Foe?

  6. U.S. Food and Drug Administration. Advice about eating fish for women who are or might become pregnant, breastfeeding mothers, and young children.

Additional Reading

By Ellen Slotkin, RD, LDN
Ellen Slotkin is a registered dietitian specializing in heart-healthy nutrition, weight management, and pregnancy nutrition.