#238 Mercury and Alzheimer’s: Does Eating Fish Increase the Risk?

Mercury and Alzheimer’s: Does Eating Fish Increase the Risk?

Studies show that eating fish protects the brain.  However, studies also show that mercury increases the risk of dementia.  So does eating fish, even if there is some mercury in it, increase or decrease your risk of Alzheimer’s disease?  Be sure to continue reading this article to find out the answer…

The Rush University Mercury, Alzheimer’s and Fish Study

Dr. Martha Clare Morris and colleagues from Rush University have been at the forefront of brain research.  In fact, Rush University is even home to the MIND Diet which is a way of eating that has been scientifically proven to protect the brain from Alzheimer’s disease and other forms of dementia.

In this study, Dr. Morris wanted to understand what mercury from eating fish does to the brain over time.  They also wanted to see if omega 3 fatty acids from fish, plants, or supplements protected the brain.  To answer this question, she studied the brains of 286 people who had already passed away.

These 286 people not only had donated their brains to Rush University but also had provided them with five years worth of food journals.  Armed with this information, Dr. Morris and her team could then connect the dots between Alzheimer’s brain changes and mercury from eating fish.

The 5 Findings of the Mercury, Fish, and Alzheimer’s Study

To come to their five conclusions, Dr. Morris and coworkers measured the amount of mercury in these donated brains.  Also, they carefully dissected each of these brains not only looking for the plaques and tangles, commonly seen with Alzheimer’s disease, but any other sign of brain damage as well.  Here is what they found:

1. The more fish people reported eating while they were alive, the more mercury researchers saw in their autopsied brains.  No surprise here.

2. Eating fish at least once a week correlated with significantly less Alzheimer’s changes to the brain in people with the Alzheimer’s gene. This finding isn’t always consistent with other studies.

For example, some studies show that fish protects everyone’s brain whereas other studies show that fish only protects the brains of people without the Alzheimer’s gene.  Regardless, there are no credible studies showing that fish is bad for your brain!

3. Plant-based omega 3s, from foods like walnuts, flax or chia seeds, protect you from strokes.  The finding that plant-based omega 3s may prevent strokes is something that has been backed up by other studies.

4. Fish oil supplements offered no protection to the brain.  This Rush University study is just one of many studies now showing that fish oil doesn’t help the brain or heart much.

5. Mercury levels in the brain from fish did not correlate with any brain damage.  This finding that moderate levels of mercury from eating fish doesn’t cause brain damage had to be the most important, and reassuring, discovery of this study.

Practical Tips

As blog readers know, I have long been interested in anything that can protect the heart and the brain.  Below are my three practical tips based on the findings of this and other studies.

1. Consider eating fish at least once a week.

In my opinion, the scientific data are now robust enough that people should consider eating fish at least once a week.  However, despite the reassuring findings of this Rush University study, mercury should be minimized to the greatest extent possible.

Just because mercury levels didn’t correlate with brain damage, doesn’t mean it isn’t causing any harm.  To minimize your mercury risk from eating fish, always look for wild, small, or ocean fish.

If wild fish is too expensive for your budget, consider shopping at places like Costco.  Given the high price of wild Alaskan salmon, our family buys all of our fish at Costco.

2. Eat plant-based omega 3s every day.

The plant-based omega 3s from foods like walnuts, chia seeds, and flax seeds have taken the back seat to fish-based omega 3s for far too long.  Plant-based omega 3s offer tremendous brain benefits without the risk of mercury and other contaminants.  Unless you have a food allergy, or are unable to digest nuts and seeds, consider eating some every day.

Our favorite way to get more plant-based omega 3s is to mix flax and chia seeds into our nut butters.  We just pour in both seeds and then stir.  You’ll love the crunchy taste these seeds give to almond butter, peanut butter, or just about any nut butter.

3. Supplements should just be supplements.

Indiscriminate use of supplements has never been shown to improve health or longevity.  Indeed, countless studies have now linked many supplements to heart disease or cancer.

Supplements should just be supplements.  In other words, supplements should only be used when it is impossible for you to get enough of a specific micronutrient from food sources.  While the benefit of fish oil has been questioned in many recent studies, at least the risk of using it seems to be very low.

Personally, I’m relieved to see the most recent data coming out on fish oil.  I never liked the after taste I used to get from swallowing the massive fish oil tablets.

What are your thoughts on fish, mercury, and Alzheimer’s disease?  Were you surprised by the findings of this study?

Please leave your thoughts and questions below.  As I respond to every question posted, the comment section will only be open for one month.  Also, if you liked this article, please be sure to read our new #1 Amazon best-selling book, The Longevity Plan, and subscribe to our free weekly newsletter and podcast!

Of course, if you are not used to eating fish or plant-based omega 3 foods, please be sure to check with your doctor first.  Also, nothing discussed in this article, or anything else from my website, should be taken as medical advice.  Always check with your doctor first before making any changes based on anything I have written or said.


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  1. I really enjoyed reading your book and I learned a lot from it. I would like to try the Longevity Soup and have found the Hemp seeds at Costco. I live in the Salt Lake City area and was wondering if you knew where I could find the pumpkin leaves. Also is there a particular type of pumpkin that I should plan on planting in my garden next year?

    Thank you.

    • Unless you grow your own garden, pumpkin greens are pretty hard to come by. I have seen them once before at Whole Foods.

      Probably the best substitution would be to use kale or spinach instead of pumpkin greens for this recipe.

      Hope this helps!


  2. Could there be an association between mercury and brain cancer? 30 years ago you never heard of brain cancer, and now I hear of a lot of people getting it (both famous and among people I know). That’s a scary disease.

    Also could mercury be a cause of neurological diseases like Parkinsons and ALS? Those seem to be increasing in frequency as well. Parkinson’s doesn’t kill you but it limits your quality of life.

    It’s a shame that we’ve let our environment get so polluted that our fish is contaminated in the first place. The one fish I like is tuna (Chicken of the Sea) but it’s probably the highest in mercury.

  3. I’m curious about why you buy fish from Costco I particular. Is their farmed salmon safer than other sources of farmed salmon? Or just cheaper, and the risk is low?

    • Hi Margot,

      The reason why we buy our fish from Costco is that their wild Alaskan salmon is cheaper than what most places charge for farmed salmon.

      Thanks for reading!


      • Oh! Thanks. I thought you were saying that Costco’s salmon was farmed. No idea why I got that idea.

        What are some of your other favorite types of fish? I hear people disparaging tilapia often. Is it worth eating?

        • Hi Margot,

          I wish I enjoyed eating fish. Unfortunately, I don’t…Thus, as I only eat fish for the health benefits, I tend to only eat wild salmon every week.

          Yes, tilapia is not the darling of the health food community. This is because tilapia is relatively low in omega 3s and very high in pollutants.

          Hope this helps!


  4. I do not understand why greater mercury in fish brains drives people to eat living fish. Personally, I like fish, so I can’t bring myself to eat them even if they are dead. What possible explanation do fish-hating people have???

    • Hi Kevin,

      Thanks for reading! For the non-fish lovers, I would recommend getting your omega 3s from other sources. Walnuts, chia seeds, and flax seeds are all excellent sources for the plant-based omega 3s. For the “fish forms” of omega 3s, you could ask your doctor about whether fish oil would be good for you or not…

      Hope this helps!


  5. hi dr. day could you kindly leave a suggested amount for nuts and seeds per day say in tablespoons for each the usual amount given is usually in a form such as handful which is vague. thank you steve

    • Hi Steve,

      For nuts, one serving in tablespoons would be 2 tablespoons which is approximately 100 calories. For seeds it would be half that amount at 1 tablespoon.

      Hope this helps!