by Dr. James Meschino on 27 December 2021 in Cancer

Mercury Levels In Fish: Advice For You And Your Patients


You know that omega-3 fats are good for you and your patients, but what about the risk of getting too much mercury in your body from eating fish on a regular fish. What fish should be avoided for this reason and which fish are safe? And can you get some additional omega-3 fats from sources other than fish? Here are the answers to those very important questions that patients often ask.

The Benefits of Omega-3 Fats

Omega-3 fats are highly beneficial to human health in that the cells of our body convert these unique fats into small hormones called prostaglandins (or eicosanoids). The prostaglandins made from omega-3 fats (Prostaglandin series 3 or PG-3) reduce risk of heart disease by opening up blood vessels and reducing the stickiness of our blood, so abnormal clots don’t form as easily. PG-2 also makes our joints and tissues less prone to inflammation, a major benefit if you have some arthritis or inflammatory bowel disease (e.g. ulcerative colitis). In addition, PG-2 has also been shown to reduce risk of cancer, as it signals our cells to replicate themselves at a slower rate. Slower cell replication reduces the chances of a genetic mutation occurring that can lead to cancer. Both animal and human studies demonstrate the anti-cancer effects of omega-3 fats. PG-2 also makes your skin smooth and soft and helps counter eczema problems. Recent studies have shown that omega-3 fat consumption can also reduce your risk of developing Alzheimer’s disease and dementia as you age. So, all in all, its worth having a strategy to get the amount of omega-3 fats to derive these available benefits.

Watching Your Mercury Intake From Fish

Fish that contain more than 1,000 mg of omega-3 fats per serving (approximately 3 ounces or 100 grams) and are low in mercury include spiny dogfish, herring, sardines, pilchards, lake trout, Atlantic sturgeon, wild Pacific salmon, anchovies, sprats, bluefish, and mullet. The following is the advice provided by the US Department of Health and Human Services (and The Environmental Protection Agency) in counseling pregnant women about fish consumption. It is a guideline for the rest of as well.

  1. Do not eat Shark, Swordfish, King Mackerel, or Tilefish because they contain high levels of mercury.
  2. Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury:
  3. Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.
  4. Another commonly eaten fish, albacore ("white") tuna, has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.

Fish and Mercury Contamination

Mercury is a mineral that exists naturally in the environment. In addition, thousands of tons are released into the air each year through pollution and waste. Bacteria and natural processes can transform mercury into the organic mercury compound methylmercury, which is a poisonous substance. Methylmercury accumulates in streams and oceans. It also accumulates in the food chain, as each fish absorbs all the mercury of the smaller fish or organisms it has eaten. That is why the oldest and largest fish, such as shark or swordfish, have the highest levels.  Studies show that methylmercury levels are higher in people who regularly eat fish.

The effects of methylmercury toxicity include paraesthesia (a pricking, tingling or creeping sensation on the skin), depression, and blurred vision. Research also suggests prenatal and infant exposure can affect attention span, language, visual-spatial skills, memory, and coordination. The National Academy of Sciences estimates that nearly 60,000 children each year are born at risk for neurological problems due to methylmercury exposure in the womb.

Vegetarian Sources Of Omega-3 Fats

In addition to fish and seafood there are omega-3-fats in some plant-based foods. However, the omega-3-fat in beans, seeds, cereals, nuts etc. is ALA (alpha-linolenic acid). Fish contain EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), which are the more famous omega-3-fats. Their famous because EPA is converted by the body into mini-hormones that directly reduce risk of heart disease (by opening up blood vessels and decreasing blood stickiness), reduce inflammation, reduce cancer risk (by slowing down cellular replication rates), while DHA is used to support brain function. However, the body can convert ALA into EPA and DHA. Scientists argue about how fast this conversion takes place, but there is ample evidence that consuming ALA from plant-based foods provides similar benefits to consuming EPA and DHA from fish. My recommendation is to have two fish servings per week, take a daily supplement containing fish, flaxseed and borage seed oil, and provide additional omega-3-fat to your body by regularly consuming plant-based foods that are rich sources of ALA. Here is a list of plant-based foods high in ALA omega-3-fat:

Food Source


Amount Of Omega-3 Fat (ALA)

Canola Oil (Organic)

1 teaspoon

0.80 gms

Flax Seed (ground up as a powder)

2 tablespoons

3.50 gms

Pumpkin Seeds

¼ cup

4.00 gms


4 ounces

0.36 gms


½ cup

4.54 gms

Salba or chia seed   

2 tablespoons

3.05g (3,050mg) 

Soy bean oil   

1 teaspoon

0.80 gms

As well, small amounts of ALA are found in kiwi fruit, black raspberries, most soy products, cauliflower, broccoli, Brussels sprouts, winter squash, turnip greens, spinach, kale, strawberries, and mustard seeds. Consuming these foods can further support your omega-3-fat nutritional status, but on their own, are likely insufficient to produce major omega-3-fat benefits. 

Foods Fortified With Omega-3-Fats – The Latest Craze

In the US more than 230 new products enriched with omega-3 hit the market this past year, with more on the way. The problem is that the amount of omega-3 being added to items like orange juice is quite small and fairly insignificant in the grand scheme of things. It’s really more marketing than science. However, fortified foods can help prop up a person’s omega-3 status, but won’t help them achieve optimal omega-3 status on their own. So, from that standpoint, a little more is better than a little less.

Food manufactures are adding omega-3 fats to spreads, salad dressings, cereals, breads, muffins etc. Just make sure that you’re not getting a ton of saturated fat, cholesterol or trans-fats from the same foods, as fats of this nature will easily undo any good provided by the added omega-3- fat. As for omega-3-fat-enriched eggs, well, they still contain 250 mg of cholesterol per yolk. Heart Disease guru Dr. Dean Ornish MD cautions against ingesting more than 100-150 mg of cholesterol on any given day. So, a three egg omelet containing, 750 mg of cholesterol, is quite likely to increase your risk of premature heart disease than any protection offered by the small amount of omega-3-fat it contains. My advice: Eat the whites and forget about the yolk altogether.

So, What’s The Game Plan

This is what I recommend as an omega-3 fat and essential fatty acid strategy:

Eat two fish servings per week, on average, choosing fish that have the highest omega-3 fat content and the lowest mercury content. Second, take a supplement each day that contains:400 mg of fish oil (mercury-free)

400 mg of flaxseed oil

400 mg of borage seed oil

I take 2-3 capsules per day of a supplement with these exact ingredients and doses. The fish oil is high in omega-3 fats (50% omega-3 fat – EPA and DHA) and is devoid of mercury and all other contaminants. The flaxseed oil is a rich source of an omega-3 fat (58% omega-3 fat) that the body can convert to the same omega-3 fats you get from fish. The borage seed oil contains a unique essential fat (GLA) that helps to suppress inflammation, improves skin softness and blocks the formation of prostaglandins that are associated with increased cancer risk.

Third, ingest vegetarian foods that can boost your omega-3 fat intake, keeping in mind that these sources contain ALA, not EPA and DHA.

This plan enables you to easily acquire the minimum of 400 mg per day of EPA/DHA that is linked to health promotion and decreased risk of dementia and Alzheimer’s disease and to acquire the ALA and GLA that help reduce inflammation, improve skin texture, and block the build up of prostaglandin series-2 end products that are linked to inflammation, heart disease and cancer.

About the Author

Dr. James Meschino, DC, MS, ROHP, is an educator, author, and researcher having lectured to thousands of healthcare professionals across North America. He holds a Master’s Degree in Science with specialties in human nutrition and biology and is recognized as an expert in the field of nutrition, anti-aging, fitness, and wellness as well as the author of numerous books.

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