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Is Eating Seafood Harmful or Beneficial For Thyroid Health?

There are many different controversies when it comes to the foods people with thyroid conditions should eat, as well as the foods which should be avoided.  One of those controversies has to do with seafood.  There are numerous health benefits associated with consuming seafood, and there are also certain risks involved.  Although all seafood has toxins, just like anything else, everything comes down to risks vs. benefits, and so one question is whether the benefits of eating seafood outweigh the risks?  In addition to the toxins present in seafood, one also has to deal with the iodine controversy.  While some healthcare professionals feel that people with thyroid conditions should consume more seafood, others recommend for people with thyroid conditions to avoid seafood due to the iodine.

What I’d like to do is start by discussing some of the benefits and risks of eating seafood:

Benefits of eating seafood:

1. Certain types of seafood can be an excellent source of omega 3 fatty acids. Fish is arguably the best food source of omega-3 fatty acids.  In this day and age most people eat way too many omega-6 fatty acids and don’t consume enough omega-3 fatty acids, which is a big reason for the rise in cardiovascular disease.

2. Seafood is a great source of protein. Obviously there are other good sources of protein, but if someone is trying to minimize their consumption of beef, pork, chicken, and other meat then seafood can be a good option.

3. Seafood can be a good source of iodine. Although there are other sources of iodine such as sea vegetables, and even dairy, some people get most or all of their iodine from consuming seafood.

Risks of eating seafood:

1. The presence of heavy metals. Methylmercury is the main heavy metal which is present in fish and other types of seafood.  And there is no question that mercury is a toxin, and can potentially trigger an autoimmune response.  However, seafood species are also high in selenium, and this in turn might offer protection from the toxic effects of mercury (1) [1].  This remains controversial, and might only be true for those who don’t have a selenium deficiency.  In other words, if someone has a selenium deficiency then the selenium they consume when eating fish might not offset the toxic effects of the mercury.

2. The presence of other toxins. In addition to methylmercury, other toxins are usually present in fish such as dioxins, polychlorinated biphenyls, polybrominated diphenyl ethers, and chlorinated pesticides (2) [2].

3. Not everyone with thyroid conditions does well with iodine. There of course is a lot of controversy when it comes to iodine and thyroid conditions.  With regards to hypothyroid conditions, iodine is required for the formation of thyroid hormone, and an iodine deficiency might lead to a decrease in thyroid hormone production.  When this is the case it would seem that eating iodine-rich foods would be beneficial, and perhaps even taking iodine supplements would be a good idea.  However, most hypothyroid conditions are autoimmune, and some people with Hashimoto’s Thyroiditis don’t do well with iodine.  Once again, there’s a lot of controversy over this, as one of the reasons why some people don’t do well with iodine is because they are low in antioxidants such as selenium and vitamin C, which are necessary to offset the potential negative effects of the oxidation reaction that takes place when iodine forms thyroid hormone.

With regards to hyperthyroid conditions, since iodine is necessary for the formation of thyroid hormone, it would seem wise for people with hyperthyroidism to avoid iodine.  However, most people with hyperthyroidism have Graves’ Disease, which is an autoimmune condition characterized by TSH receptor antibodies which attack the TSH receptors, and this is what’s responsible for the high thyroid hormone levels.  Taking iodine usually won’t cause an excess of thyroid hormone production, and in fact, before radioactive iodine was used as a treatment, iodine supplementation was commonly recommended in those with hyperthyroid conditions.  With that being said, while most people with Graves’ Disease seem to do fine eating iodine-rich foods, every now and then someone won’t do well.

How Much Iodine Is Present In Seafood?

Not surprisingly, different types of seafood will have different amounts of iodine.  Scallops, cod, and shrimp appear to have some of the highest levels of iodine.  Tuna, salmon, and sardines also have high levels of iodine, although not as much.  But keep in mind that when I say “high levels”, this is in relationship to the recommended daily intake (RDI).  The RDI for iodine in adults is 150 mcg (3) [3].  For most fish the content of iodine usually ranges from between 25 to 140 micrograms per 4-ounce servings (4) [4].  For example, a 4-ounce serving of cod has approximately 132 mcg of iodine, while a 4-ounce serving of salmon will have 32 mcg of iodine (3) [3].

In most cases, the iodine content of seafood won’t cause problems in those with thyroid and autoimmune thyroid conditions, and so eating a few servings of seafood per week usually is fine.  On the other hand, sea vegetables such as kelp have much larger amounts of iodine, and possibly can be problematic in some people with thyroid and autoimmune thyroid conditions.  I realize that some healthcare professionals recommend for people with Graves’ Disease and Hashimoto’s Thyroiditis to completely avoid iodine, even from food sources.  And while every now and then someone with these conditions will have problems even with small amounts of iodine from food sources, in most cases this isn’t an issue.  And so very rarely do I tell someone to avoid eating seafood out of fear of them reacting to iodine.

Which Fish Have The Highest Levels Of Mercury?

Typically the larger fish will have higher amounts of mercury, as well as other toxins.  According to the Environmental Protection Agency, shark, swordfish, king mackerel, and tilefish contain high levels of mercury, and thus shouldn’t be eaten (5) [5].  They also mention how shrimp, canned light tuna, salmon, pollock, and catfish have lower levels of mercury.  However, most other types of tuna has higher amounts of mercury.  The Natural Resources Defense Council has a list of seafood [6] with the least amount of mercury, those with a moderate mercury content, and those with a high mercury content.  And for those people who love eating lobster, keep in mind that lobster is lower in omega-3 fatty acids, and according to the Environmental Working group it should be avoided by pregnant and women due to the mercury content.

Do The Risks of Eating Seafood Outweigh The Benefits?

As I mentioned earlier, I’m not too concerned about the risks of consuming seafood due to the iodine content, as this rarely is a problem.  However, I am concerned about the levels of toxins present in seafood.  And while one can argue that the selenium in seafood might protect us against the side effects of these toxins, especially mercury, the truth is that the selenium content of seafood probably hasn’t changed much over the last hundred years, but of course the amount of toxins in the lakes, rivers, and oceans have greatly increased.  There is no question that the seafood of today is more toxic than the seafood our ancestors ate in the past.

However, the same of course is true with other foods as well.  Fruits and vegetables are more toxic than they were in the past, and even if you buy organic fruits and vegetables this still doesn’t guarantee that they’re free from pesticides.  No matter what we do we can’t completely avoid exposure to toxins.  When it comes to seafood, I think it’s fine for most people to eat two or three servings of low-mercury fish per week.  But this also might depend on their toxic load, as if they obtain a test for toxic metals and test positive for high levels of methylmercury, then it might be best to either completely avoid fish, or perhaps limit their consumption one or two servings per week.  Another factor could be their glutathione levels, which plays an important role in detoxification.  Someone with normal glutathione levels might be able to eat more fish than another person with lower glutathione levels.  Perhaps a bigger factor is whether or not the person’s immune system reacts to mercury, which can be measured through tests such as the Chemical Immune Reactivity Screen by Cyrex Labs.

In summary, there is some controversy over whether people with thyroid and autoimmune thyroid conditions should consume seafood.  Although there are some great health benefits of eating seafood, there are some potential risks as well.  While some people are concerned about the iodine present in seafood, in most cases the iodine content isn’t high enough to cause problems in people with thyroid and autoimmune thyroid conditions.  On the other hand, the presence of methylmercury and other toxins is a risk that needs to be considered.  I think it’s fine for most people to eat two to three servings per week of fish with lower amounts of mercury, while those with a high mercury content should be completely avoided.