Fish Oil and Thyroid Relationship (Should you supplement?)

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Fish oil is a supplement that supplies your body with Omega-3 fatty acids that are essential for our health and wellbeing.

According to the National Center for Complementary and Integrative Health, fish oil was the most popular natural product among US adults in 2012 (the last year for which info is available) with 7.8% people reporting they used these products regularly.

About 8 million more people used fish oil in 2012 compared to 2007[i]. Regular intake of fish oil provides various health benefits, but how does it affect your thyroid?

We aimed to find out.

Fish oil and hypothyroidism

Even though benefits of fish oil for our overall health and management of different diseases and conditions are well-documented, there is still not enough research about its impact on hypothyroidism.

While it is important to carry out more studies to find out more about the effect of fish oil on this common thyroid disorder, some studies confirmed it has a positive influence on your gland.

Liver function

First, it is important to mention that fish oil has the tremendous potential to improve liver function. The liver is the organ that processes most fat in a person’s body and it plays a big role in weight management.

Inadequate liver function contributes to weight gain, which happens to be a major symptom of hypothyroidism too.

The prevalence of liver diseases is on the rise, particularly non-alcoholic fatty liver disease, which occurs due to the accumulation of fat in the liver.

Evidence shows that Omega-3 fatty acids, found in fish oil, decrease liver fat[ii] by as much as 50%[iii] thus improving overall liver function.

Why is this important?

Well, your liver pays a huge role in the functioning of thyroid gland and vice versa.

Thyroid hormones thyroxine (T4) and tri-iodothyronine (T3) regulate the basal metabolic rate of all cells, including hepatocytes (liver cells), thereby modulating the function of your liver too. As a result, the liver metabolizes hormones produced by the thyroid and regulates their endocrine effects.

Thyroid disorders disrupt the function of the liver just like liver problems modulate thyroid hormone metabolism[iv]. Basically, thyroid hormones need a healthy liver, just like this organ needs healthy thyroid in order to function properly.

Their efficacy and function go hand in hand.

The Journal of Nutritional Biochemistry published a study which evaluated the impact of fish oil on thyroid hormone signaling in the liver.

Results showed that serum total T3, T4, and thyrotropin were similar between mice that received fish oil and soybean oil, but the first one had more favorable effects overall.


Scientists discovered that expression of liver thyroid hormone receptor (TR) β1 protein was higher in fish oil group.

Moreover, liver 5’-deiodinase activity, which is responsible for converting T4 into T3 hormone, was similar between the groups but animals that received fish oil also exhibited the improved activity of hepatic mitochondrial glycerophosphate dehydrogenase.

This is an enzyme that plays a role in thermogenesis and a target stimulated by thyroid hormone T3 through TRβ1 receptor. Scientists concluded that fish oil supplementation enhances thyroid hormone action in the liver[v].

Bearing in mind that fish oil has a favorable impact on liver action and thyroid production, it could help prevent or manage hypothyroidism.

Lipid balance

Not only did the above-mentioned study confirm the positive influence of fish oil on thyroid hormone production and liver health, but it revealed a potential mechanism involved in lipid metabolism.

Omega-3 fatty acids, found in fish oil supplements, are well-known for their positive influence on cholesterol levels in your body.

Studies show that regular intake Omega-3s reduces plasma triglyceride levels[vi] and some evidence reveals these healthy fats have a positive impact on HDL (good) cholesterol[vii].

Unhealthy cholesterol levels increase the risk of cardiovascular diseases, but thyroid function also plays a role in lipid profile.

Hypothyroidism, a common thyroid disorder, is strongly associated with increased levels of total cholesterol, LDL (bad) cholesterol, higher triglyceride levels, and reduce the concentration of HDL cholesterol.

A growing body of evidence confirms that thyroid dysfunction has a major impact on your lipid profile which is why biochemical screening for thyroid dysfunction is recommended for all patients who experience unexpected worsening or improvement of lipid profile.

Thyroid hormones induce the HMG-CoA (3-hydroxy-3-methylgutaryl-coenzyme A) reductase, the first step in cholesterol biosynthesis. In addition, T3 upregulates LDL receptors by controlling the LDL receptor gene activation.

At the same time, this hormone also regulates LDL receptor’s gene expression and it protects LDL from oxidation. Thyroid hormones also influence HDL metabolism and take place in many other metabolic processes[viii].

If we bear in mind that hypothyroidism negatively affects lipid profile and fish oil consumption improves it, we can consider it yet another way this healthy fat helps people with hypothyroidism.

Of course, more research on this topic is necessary to determine how exactly fish oil helps us balance out lipid profile.

Protects from cognitive impairment

In many cases, hypothyroidism is linked to decreased cognitive abilities. One study showed that hypothyroid patients had worse memory states than their healthy counterparts. Also, hypothyroid participants had decreased task-induced deactivation during working memory processing[ix].

Adequate thyroid function is vital for healthy development and retention of cognitive function, throughout your lifetime. The relationship between thyroid hormone levels and cognitive function has been recognized ever since scientists discovered that cretinism stems from thyroid and iodine deficiencies.

Underactive thyroid gland causes deterioration of cognitive abilities, regardless of your age, because hypothyroidism doesn’t allow the brain to sustain the glucose-consuming processes which are important for energy, neurotransmission, memory, and other functions.

Common cognitive effects recorded in middle-aged hypothyroid patients include diminished general cognition, memory, attention, learning, and psychomotor speed. Even though cognitive deficits are mainly characteristic for hypothyroidism, some hyperthyroid patients can experience them as well.

In hyperthyroidism, the impaired cognitive functions are less severe than in hypothyroid individuals[x].

As you can see, it’s not uncommon for hypothyroidism (and hyperthyroidism to some extent) to induce changes in cognitive abilities, but this is where fish oil steps in. A team of scientists from Egypt discovered that supplementation with Omega-3 fatty acids ameliorated memory deficits in hypothyroid rats.

Also, intake of these healthy fats increased total antioxidant capacity and decreased structural changes that occurred due to hypothyroidism.

In addition, Omega-3s reduced the expression of protein Cav1.2 which plays a role in inflammation, stress etc. Scientists concluded that Omega-3 fatty acids could serve as neuroprotective agent in hypothyroidism-caused cognitive impairment[xi].

Fish oil and oxidative stress

Oxidative stress is an imbalance between the production of free radicals and the body’s ability to counteract or neutralize their harmful effects through the activity of antioxidants.

It is a well-known fact that oxidative stress contributes to a number of health conditions, including cancer.

A growing body of evidence confirms that thyroid disorders are usually associated with increased oxidative stress.

For example, hypothyroidism appears to be a state of enhanced oxidative stress, but levothyroxine treatment helps reduce it[xii].

Although oxidative stress is strongly expressed in both hypo- and hyperthyroidism, the mechanisms by which it is generated are different.

In hypothyroidism, oxidative stress is a result of the low availability of antioxidants while in hyperthyroid patients it occurs due to increased reactive oxygen species (ROS) production.

In hyperthyroidism, some complications are caused by oxidative stress because thyroid hormones (which are produced excessively) can act as oxidants and induce DNA damage.

On the other hand, in hypothyroidism oxidative stress can disturb lipid profile entirely[xiii].

Regular intake of fish oil has the potential to reduce oxidative stress. A study from the Free Radical Research revealed that both EPA and DHA (types of Omega-3 fatty acids) decrease oxidative stress by as much as 24%[xiv].

Fish oil and inflammation

Inflammation is a natural response of your body to injury, trauma, and stress. Despite the fact that a certain level of inflammation is important for our health, chronic and persistent inflammation plays a role in the development of many diseases.

Impaired thyroid function also contributes to inflammation.

For instance, one study found that hypothyroidism is linked with low-grade inflammation in men under 50 years of age[xv].

Fish oil exhibits anti-inflammatory effects through a variety of mechanisms. Many of these mechanisms are linked with changes in the fatty acid composition of cell membranes.

Alterations in these compositions modify membrane fluidity and cell signaling thus leading to altered gene expression and the pattern of lipid mediator production.

As a result of their anti-inflammatory effects, marine sources of Omega-3 fatty acids (fish oil primarily) have a major therapeutic efficacy and could protect us from different health conditions caused by excessive inflammation[xvi].

Evidence also shows that supplementation with fish oil also proves to be beneficial for patients with autoimmune diseases[xvii].

This is particularly important if we bear in mind that autoimmune conditions like Graves’ disease and Hashimoto’s thyroiditis are related to hyperthyroidism and hypothyroidism respectively.

Fish oil and weight management

Weight is often correlated with the levels of thyroid hormones in the body. Thyroid hormones regulate basal metabolism in your body and they also take part in thermogenesis and lipid and glucose metabolism. In addition, thyroid hormones levels also play a role in food intake and fat oxidation.

Hypothyroid patients show decreased thermogenesis, metabolic rate, and they also have a higher BMI. What’s more, even mild thyroid dysfunction can induce major body weight changes[xviii].

Benefits of fish oil on weight management are well-documented. A study from the American Journal of Clinical Nutrition found that fish oil supplementation lowered triglyceride levels, increased HDL cholesterol, and reduce body fat in participants[xix]. The International Journal of Obesity published an interesting study which found that the inclusion of fatty fish or fish oil into the energy-restricted diet resulted in about 1kg more weight loss after four weeks than did nutrition plan without fish oil or fatty fish. Scientists concluded their study explaining that fish oil boosts weight loss[xx].

How much fish oil I need a day?

Fish oil supplements come in liquid, capsule, and pill form. At this point, there is no specific daily value you should be taking like with vitamins and minerals.

That being said, different health organizations have released their expert opinions regarding daily intake of fish oil, but they vary from one organization to another.

In most cases, it is recommended that adults take 250-500mg EPA and DHA combined per day.

If you want to manage your thyroid disorder with fish oil or use this supplement to prevent any potential problem with this butterfly-shaped gland, follow your doctor’s or manufacturer’s recommendations.


Fish oil is the most commonly used supplement primarily because it supports overall health and does a great job in prevention and management of different conditions.

Despite it is thoroughly studied, there is a lot we don’t know about thyroid and fish oil relationship due to the lack of data. Perhaps this is why most thyroid supplements do not currently include fish oil in their supplement ingredients.

Fish oil supplementation may improve thyroid function through multiple mechanisms including liver health, weight management, anti-inflammatory, and antioxidant effects.


[i] Most used natural products, National Center for Complementary and Integrative Health

[ii] Parker HM, Johnson NA, Burdon CA, et al. Omega-3 supplementation and non-alcoholic fatty liver disease: a systematic review and meta-analysis. Journal of Hepatology 2012 Apr;56(4):944-51. Doi: 10.1016/j.hep.2011.08.018

[iii] Spadaro L, Magliocco O, Spampinato D, et al. Effects of n-3 polyunsaturated fatty acids in subjects with nonalcoholic fatty liver disease. Digestive and Liver Disease 2008 Mar;40(3):194-9. Doi: 10.1016/j.did.2007.10.003

[iv] Malik R, Hodgson H. The relationship between the thyroid gland and the liver. QJM: An International Journal of Medicine 2002 Sep, 95(9):559-569. Doi: 10.1093/qjmed/95.9.559

[v] Souza LL, Nunes MO, Paula GS, et al. Effects of dietary fish oil on thyroid hormone signaling in the liver. Journal of Nutritional Biochemistry 2010 Oct;21(10):935-40. Doi: 10.1016/j.jnutbio.2009.07.008

[vi] Goh YK, Jumpsen JA, Ryan EA, Clandinin MT. Effect of Omega-3 fatty acid on plasma lipids, cholesterol, and lipoprotein fatty acid content in NIDDM patients. Diabetologia 1997 Jan;40(1):45-52

[vii] Burillo E, Martin-Fuentes P, Mateo-Gallego R, et al. Omega-3 fatty acids and HDL. How do they work in the prevention of cardiovascular disease? Current Vascular Pharmacology 2012 Jul;10(4):432-41

[viii] Rizos C., Elisaf M., Liberopoulos E. Effects of Thyroid Dysfunction on Lipid Profile. The Open Cardiovascular Medicine Journal. 2011;5:76-84. doi:10.2174/1874192401105010076.

[ix] He XS, Ma N, Pan ZL, et al. Functional MRI assessment of altered brain function in hypothyroidism during working memory processing. European Society of Endocrinology 2011 Apr,

[x] Bégin ME, Langlois MF, Lorrain D, Cunnane SC. Thyroid Function and Cognition during Aging. Current Gerontology and Geriatrics Research. 2008;2008:474868. doi:10.1155/2008/474868.

[xi] Abd Allah ES, Gomaa AM, Sayed MM. The effect of Omega-3 on cognition in hypothyroid adult male rats. Acta Physiologica Hungarica 2014 Sep;101(3):362-76. Doi: 10.1556/APhysiol.101.2014.3.11

[xii] Chakrabarti SK, Ghosh S, Banerjee S, Mukherjee S, Chowdhury S. Oxidative stress in hypothyroid patients and the role of antioxidant supplementation. Indian Journal of Endocrinology and Metabolism. 2016;20(5):674-678. doi:10.4103/2230-8210.190555.

[xiii] Mancini A, Di Segni C, Raimondo S, et al. Thyroid hormones, oxidative stress, and inflammation. Mediators of Inflammation 2016 Feb. Doi: 10.1155/2016/6757154

[xiv] Mas E, Woodman RJ, Burke V, et al. The Omega-3 fatty acids EPA and DHA  decrease plasma F(2)-isoprostanes: results from two placebo-controlled interventions. Free Radical Research 2010 Sep;44(9):983-90. Doi: 10.3109/10715762.2010.492830

[xv] Kvetny J, Heldgaard PE, Bladbjerg EM, Gram J. Subclinical hypothyroidism is associated with a low-grade inflammation, increased triglyceride levels, and predicts cardiovascular diseases in males below 50 years. Clinical Endocrinology 2004 May,61:232-238. Doi: 10.1111/j.1365-2265.2004.02088.x

[xvi] Calder PC. Omega-3 Fatty Acids and Inflammatory Processes. Nutrients. 2010;2(3):355-374. doi:10.3390/nu2030355.

[xvii] Simopoulos AP. Omega-3 fatty acids in inflammation and autoimmune diseases. Journal of the American College of Nutrition 2002 Dec;21(6):495-505

[xviii] Sanyal D, Raychaudhuri M. Hypothyroidism and obesity: An intriguing link. Indian Journal of Endocrinology and Metabolism. 2016;20(4):554-557. doi:10.4103/2230-8210.183454.

[xix] Hill AM, Buckley JD, Murphy KJ, Howe PR. Combining fish oil supplements with regular aerobic exercise improves body composition and cardiovascular disease risk factors. American Journal of Clinical Nutrition 2007 May;85(5):1267-74

[xx] Thorsdottir J, Tomasson H, Gunnardottir I, et al. Randomized trial of weight loss diets for young adults varying in fish and fish oil content. International Journal of Obesity 2007 Oct;31(10):1560-6. Doi: 10.1038/sj.ijo.0803643

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