Thyroid and Vitamin B12 Relationship

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We have the amazing opportunity to protect thyroid and its functioning by avoiding or limiting consumption of foods with a negative impact on the gland.

At the same time, increased intake of nutritious foods can improve thyroid health and help us prevent or manage common disorders.

A number of different nutrients, primarily vitamins, and minerals, are well-known for their ability to benefit thyroid functioning. This post is going to focus on vitamin B12.

Scroll down to learn more about a relationship between this vitamin and thyroid health.

Vitamin B12 brief overview

Let’s start with a simple overview to get to know this vitamin a little bit better.

Vitamin B12, whose formal name is Cobalamin, is just one of eight B complex vitamins.

Generally, B complex vitamins help the body convert carbohydrates into glucose or fuel for energy.

These vitamins also help the body use proteins and fats. As you are already aware, all vitamins from B complex are vital for overall health and wellbeing.

Vitamin B12 is water-soluble. Basically, the vitamin dissolves in water and then travels through the bloodstream in order to deliver its health benefits.

This micronutrient is particularly important for maintaining nerve cells’ health and functioning. Vitamin B12 also participates in production of genetic material i.e. DNA and RNA[i].

Together with vitamin B9 (folic acid, folate), vitamin B12 works to improve efficacy and functioning of iron and to produce red blood cells.

Functioning of the brain and nervous system and metabolism of every cell in your body require sufficient levels of vitamin B12.

While your body produces millions of red blood cells every minute, they cannot function adequately or multiply without this vitamin. Since cobalamin has a significant influence on our entire body, does it also play a role in thyroid health?

Let’s see.

Vitamin B12 and hypothyroidism

Before we move on, if you see a term or phrase that you don’t really understand, check out our frequency asked questions series found on Common Thyroid Questions and Answers.

OK, back to the topic.

Many hypothyroid patients are deficient in some vitamins and minerals, including vitamin B12.

One study enrolled 116 hypothyroid patients who were evaluated for signs and symptoms of vitamin B12 deficiency.

Scientists discovered that 46 or 39.6% participants had low levels of this micronutrient.

The prevalence of vitamin B12 deficiency was equal in both men and women.

Based on the discovery that about 40% of hypothyroid patients are deficient in this vitamin, scientists emphasized the importance of screening people with hypothyroidism for vitamin B12 levels. Replacement of vitamin B12 leads to improvement of symptoms[ii] patients experience.

In addition, evidence shows that pernicious anemia affects hypothyroid patients 20 times more frequently than other people[iii]. Pernicious anemia is a condition that occurs when the body doesn’t absorb sufficient amount of cobalamin.

This form of anemia is called pernicious due to the fact it was considered a deadly disease back in time. The primary reason why pernicious anemia was deadly in the past was due to the lack of adequate treatment.

Nowadays, it is possible to treat and manage this condition with vitamin B12 injections and supplements.

Hypothyroidism can cause vitamin B12 deficiency

Symptoms of vitamin B12 deficiency are quite similar to symptoms of hypothyroidism, which is why it is usually overlooked.

A hypothyroid person who experiences symptoms linked with vitamin B12 deficiency can assume he/she is experiencing those unfortunate scenarios due to their condition and vice versa.

Hashimoto’s thyroiditis, the most common cause of hypothyroidism, can induce intestinal damage that affects the body’s ability to absorb this vitamin. As a result, a person with

Hashimoto’s who consumes sufficient amount of this micronutrient can still experience symptoms of deficiency because his/her body didn’t absorb the vitamin adequately.

A solution to this problem is addressing the thyroid problem in order to enhance absorption of vitamin B12.

Previous research investigated the association between hypothyroidism and high homocysteine levels. Homocysteine is an amino acid and a breakdown product of protein metabolism that increases the risk of heart disease and stroke when present in high concentrations.

The study included 14 hypothyroid patients who were diagnosed with hyperhomocysteinemia, abnormally high homocysteine levels. Patients received a treatment with l-thyroxine (T4).

Scientists discovered that homocysteine levels returned to normal values as hypothyroidism was resolved. This finding led to a conclusion that hyperhomocysteinemia is caused by hypothyroidism[iv] and it is possible to manage the condition successfully.

Why is this related to vitamin B12?

Homocysteine is a metabolite of the crucial amino acid methionine which requires vitamin B12 and folate for the synthesis process. The insufficient levels of these vitamins lead to the accumulation of homocysteine in the body.

As a result, homocysteine becomes toxic to nervous and cardiovascular systems. That’s why supplementation with vitamin B12 or folate is necessary in case of deficiency in one or both micronutrients – to prevent accumulation.

Thyroid hormones take part in folate synthesis and since this micronutrient and vitamin B12 do share different biochemical processes, then these hormones also influence cobalamin levels.

Basically, hypothyroidism can lead to vitamin B12 deficiency especially if we bear in mind that the condition affects absorption of the micronutrient.

Vitamin B12 deficiency and hypothyroidism symptoms

As shown above, vitamin B12 deficiency and hypothyroidism symptoms are similar, which is why this problem is largely overlooked among hypothyroid patients. For a comparison’s sake, here are the most common symptoms of both vitamin B12 deficiency and hypothyroidism.

Vitamin B12 deficiency:

  • Behavioral changes
  • Depression
  • Fatigue
  • Headache
  • Lightheadedness
  • Memory loss
  • Muscle weakness
  • Pale skin
  • Vision loss


  • Decreased libido
  • Depression
  • Dry skin
  • Fatigue
  • Memory problems
  • Menstrual period issues
  • Muscle weakness
  • Pain and stiffness in your joints
  • Slowed heart rate

Immune system and vitamin B12

A growing body of evidence confirms that vitamin B12 exhibits immunomodulatory effects[v]. One study discovered that although this vitamin doesn’t affect the immune system of rats that were fed the standard diet for 30 days, it has a beneficial impact on protein-deficient animals[vi].

Supplementation with vitamin B12 strengthened the immune system of rats that didn’t consume sufficient amount of protein, thus confirming that adequate intake of this micronutrient is vital for good overall health and wellbeing.

The positive impact of vitamin B12 on the immune system is particularly important if we bear in mind that thyroid hormones T3 and T4 modulate immune activity on a cellular level[vii].

Evidence shows that thyroid hormones play a big role in regulating lymphocyte reactivity[viii].

Lymphocytes are a type of white blood cells generated by the immune system to defend the body against pathogens, cancerous cells, viruses, bacteria, and diseases.

Cognitive functioning and vitamin B12

Vitamin B12 influences numerous processes and functions in your body. Besides its impact on the immune system and production red blood cells, this micronutrient also benefits your cognitive abilities.

Studies show that neurotoxic effects of homocysteine may play a role in the neurologic and psychiatric disturbances associated with a deficiency in folate and vitamin B12[ix].

Thanks to its role in nerve health and neurotransmitter signaling, vitamin B12 positively influences cognitive function which is why it is used to decrease the risk of neurodegenerative diseases like dementia and Alzheimer’s disease[x].

As seen above, hypothyroidism is strongly related to memory problems and weaker cognitive functioning. In fact, this thyroid disorder may be a predisposing factor for cognitive impairment. That is because thyroid function is an important factor in retaining optimal cognition during the aging process.

Many studies suggest there is a continuum characterizing the influence of thyroid function on cognition wherein cognitive dysfunction results either from chronically decreased or increased concentration of thyroid hormones[xi].

Other benefits of vitamin B12

Sufficient intake of vitamin B12 is essential for our overall health and wellbeing.

Now that we have established healthy levels of the vitamin have a positive influence on thyroid functioning, especially for hypothyroid individuals, let’s see some other health benefits linked with this micronutrient. They are:

  • Anemia prevention – deficiency in vitamin B12 leads to anemia primarily because this vitamin is essential for production of red blood cells
  • Better mood – together with folate, vitamin B12, is also necessary for production of s-adenosyl methionine (SAM), a compound that is crucial for neurological function, mood regulation, and stress management
  • Healthy skin and hair – vitamin B12 takes part in the production of cells, thus contributing to healthy skin, hair, and nails. Plus, this amazing vitamin also reduces skin redness, dryness, acne blemishes, and inflammation. Sufficient level of vitamin B12 prevents hair breakage and makes the bones stronger. See more here.
  • Heart health – due to its ability to regulate levels of homocysteine, vitamin B12 maintains heart health and prevents different cardiovascular diseases. The micronutrient is also linked with healthy cholesterol levels and regulation of blood pressure
  • Improved digestion – one of many effects of vitamin B12 is the ability to foster healthy bacteria in a person’s gut. Digestive health and prevention of diseases affecting the GI tract occur thanks to the elimination of harmful bacteria and generating presence of good or beneficial bacteria in return
  • Maintaining energy levels – vitamin B12 is vital for healthy metabolism because the body needs it to convert carbs into glucose that our body uses for energy. Since the body uses vitamin B12 to produce energy, it comes as no wonder why deficiency in this micronutrient induces fatigue
  • Safe and healthy pregnancy – expectant mothers need to consume a variety of nutrients to stay healthy and ensure their baby develops properly. During this special time in a woman’s life, vitamin B12 is crucial for creating nucleic acid or DNA

Recommended daily intake of vitamin B12

As mentioned throughout this post, sufficient levels of vitamin B12 are crucial for proper functioning of the entire body, including your thyroid gland. Taking supplements or foods containing this vitamin isn’t enough; you have to meet daily requirements. But, how much do you need on a daily basis? According to the National Institutes of Health, the recommended daily intake of vitamin B12 is[xii]:

  • 0-6 months: 0.4 mcg
  • 7-12 months: 0.5 mcg
  • 1-3 years: 0.9 mcg
  • 4-8 years: 1.2 mcg
  • 9-13 years: 1.8 mcg
  • 14+ years: 2.4 mcg

Sources of vitamin B12

Like with many other nutrients, it is possible to obtain recommended daily values of vitamin B12 through diet. The best sources of the micronutrient include:

  • Beef liver
  • Chicken
  • Cottage cheese
  • Eggs
  • Fortified cereal
  • Grass-fed beef
  • Low-fat milk and yogurt
  • Nutritional yeast
  • Salmon
  • Sardines
  • Trout
  • Turkey

Since major sources of vitamin B12 are meat-based vegans and vegetarians obtain daily amounts through the intake of supplements.

If you’re considering using supplements to improve thyroid health, it is always a good idea to check with your doctor first. We also have a guide to different kinds of thyroid supplements on this website (link here), ranked based on the effectiveness of the thyroid supplement.


Vitamin B12 is crucial for the production of red blood cells, improves metabolism, and so much more.

Basically, your body needs this vitamin to stay healthy. The thyroid also requires sufficient levels of vitamin B12 primarily because a deficiency in this vitamin is common among hypothyroid patients.

Strive to consume recommended daily value of this vitamin for optimal health and thyroid functioning.


[i] Vitamin B12 (Cobalamin), University of Maryland Medical Center

[ii] Jabbar A, Yawar A, Waseem S, et al. Vitamin B12 deficiency common in primary hypothyroidism. Journal of the Pakistan Medical Association 2008 May;58(5):258-61

[iii] Antonijević N, Nesović M, Trbojević B, Milosević R. Anemia in hypothyroidism. Medicinski Pregled 1999 Mar-May;52(3-5):136-40

[iv] Catargi B, Parrot-Roulaud P, Cochet C, et al. Homocysteine, hypothyroidism, and effect of thyroid hormone replacement. Thyroid January 2009, 9(12):1163-1166. Doi: 10.1089/thy.1999.9.1163

[v] TAMURA J, KUBOTA K, MURAKAMI H, et al. Immunomodulation by vitamin B12: augmentation of CD8+ T lymphocytes and natural killer (NK) cell activity in vitamin B12-deficient patients by methyl-B12 treatment. Clinical and Experimental Immunology. 1999;116(1):28-32. doi:10.1046/j.1365-2249.1999.00870.x.

[vi] Lewicki S, Lewicka A, Kalicki B, Kłos A, Bertrandt J, Zdanowski R. The influence of vitamin B12 supplementation on the level of white blood cells and lymphocytes phenotype in rats fed a low-protein diet. Central-European Journal of Immunology. 2014;39(4):419-425. doi:10.5114/ceji.2014.47723.

[vii] De Vito P, Incerpi S, Pedersen JZ, et al. Thyroid hormones as modulators of immune activities at the cellular level. Thyroid 2011 Aug;21(8):879-90. Doi: 10.1089/thy.2010.0429

[viii] Klecha AJ, Genaro AM, Gorelik G, et al. Integrative study of hypothalamus-pituitary-thyroid-immune system interaction: thyroid hormone-mediated modulation of lymphocyte activity through the protein kinase C signaling pathway. Journal of Endocrinology 2006 Apr;189(1):45-55. Doi: 10.1677/joe.1.06137

[ix] Bottiglieri T. Folate, vitamin B12, and neuropsychiatric disorders. Nutrition Reviews 1996 Dec;54(12):382-90

[x] H.-X.Wang. Vitamin B12, folate, and Alzheimer’s disease. Drug Development Research June 2002, vol. 56 no. 2, 111-122. Doi: 10.1002/ddr.10066

[xi] 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.

[xii] Vitamin B12, National Institute of Health

1 Comment
  1. Reply
    Heulwen Harris August 28, 2020 at 10:06 am

    Simple question but NOT a simple answer!!!!!!

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