Effects of Vitamin C on the Thyroid

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Vitamin C, also known as ascorbic acid, has numerous functions in a human body.

The vitamin is required for biosynthesis of collagen, protein metabolism, functions as an antioxidant, and strengthens our immune system to prevent infections, cold and flu.

Humans are not able to synthesize vitamin C, so it is a crucial dietary component.

Benefits of this micronutrient for different aspects of our health are well-documented, but what about thyroid?

This article aims to elucidate the effects of vitamin C on thyroid and its functioning.

Oxidative stress and thyroid

Oxidative stress is defined as an imbalance between the production of free radicals and the body’s ability to detoxify or counteract their harmful effects through neutralization by antioxidants.

Numerous factors are linked to oxidative stress including thyroid hormones.

Evidence shows that oxidative stress is strongly associated with both hypothyroidism and hyperthyroidism[i].

Despite the fact that oxidative stress is linked to both hypo- and hyperthyroidism, the underlying mechanisms are entirely different.

Hyperthyroidism is associated with increased reactive oxygen species or ROS (chemically reactive species containing oxygen) while hypothyroidism is connected to the low availability of antioxidants.

It is also important to mention that thyroid itself can be damaged by oxidative stress, particularly in the case of iodine excess.

Studies show that excess of iodide in a thyroid may result in mitochondrial oxidative stress, which leads to a damage of thyrocytes[ii] (thyroid epithelial cells).

Furthermore, some complications of hyperthyroidism in target tissues are caused by oxidative stress, according to a study whose findings were published in the Free Radical Biology and Medicine[iii].

Evidence also shows that tissue hypothyroidism can worsen oxidative stress[iv].

Vitamin C steps in to combat oxidative stress

Bearing in mind that both hypothyroidism and hyperthyroidism are directly or indirectly linked to oxidative stress, vitamin C can help regardless of the condition you have.


The answer is because it acts as an antioxidant[v].

Antioxidant supplementation proves to be effective in individuals with hypothyroidism.

In one study, scientists enrolled 33 patients with primary hypothyroidism who were compared with 26 healthy controls.

Serum MDA (marker of oxidative stress) levels were higher in patients with hypothyroidism before the antioxidant treatment compared to controls.

After the treatment, MDA levels in participants with hypothyroidism decreased significantly[vi].

Similarly to hypothyroidism, studies found that Graves’ hyperthyroidism is characterized by increased oxidative stress.

What’s more, free radicals might be responsible for some symptoms and signs of hyperthyroidism[vii].

An antioxidant treatment which included ascorbic acid or vitamin C improved the antioxidant defense symptoms in 24 hyperthyroid patients and relieved oxidative stress[viii].

Evidence of oxidative stress in thyroid disorders and the role of antioxidants keeps mounting.

One study revealed that consequent antioxidant therapy should be incorporated with thyroid replacement therapy such as Synthroid or Armour Thyroid.

The same research also confirmed oxidative stress is present in both hyper- and hypothyroidism and highlighted the role of antioxidant vitamins E and C.

Vitamin C is a powerful antioxidant due to its ability to reduce the tocopherol back to alpha tocopherol[ix] (vitamin E).

Enhanced hormone absorption

Hypothyroidism is a disorder indicated by underactive thyroid gland i.e. the production of hormones is insufficient. It has many causes including nutrient deficiencies, genetics, etc.

The primary treatment option for this disorder is an intake of levothyroxine, a synthetic thyroid hormone whose brand names include Synthroid, Levoxyl, Unithroid, and Tirosint[x].

However, malabsorption of levothyroxine is a common clinical problem.

One study aimed to discover the effect of vitamin C on the absorption of levothyroxine in individuals with hypothyroidism and gastritis.

The study included 31 patients with hypothyroidism (28 women and 3 men) who ingested the dose of levothyroxine in 120ml water containing 500mg vitamin C.

Scientists found that serum concentrations of TSH, free T4, and T3 improved while participants were taking vitamin C together with their medication.

The research team concluded vitamin C improves the abnormalities in serum T4, T3, and TSH concentrations in hypothyroidism patients[xi] and the method could be helpful for management of this health problem.

Memory improvement

Thyroid hormones regulate metabolism in every organ of your body, including the brain.

When the production of thyroid hormones is low, in the case of hypothyroidism, it can affect memory and concentration of an individual.

Evidence shows deficits in verbal memory are strongly linked to hypothyroidism[xii], which can have a major impact on overall quality of life.

Verbal memory deficits were also found in adolescents with congenital hypothyroidism[xiii].

This is yet another way vitamin C can help improve thyroid function naturally.

A study whose findings were published in the Metabolic Brain Disease discovered that vitamin C has beneficial effects on learning and memory.

The research also confirmed supplementation with vitamin C has protective effects on hypothyroidism-related learning and memory impairment in juvenile rats which may be elucidated by antioxidant effects[xiv].

Cholesterol management

The body needs thyroid hormones to make cholesterol as well as to get rid of the cholesterol it doesn’t need.

In people with hypothyroidism, the body doesn’t break down and remove LDL or bad cholesterol as efficiently as it should.

As a result, LDL cholesterol builds up in the blood. Higher levels of LDL cholesterol are a major risk factor for cardiovascular diseases.

One study analyzed the effects of antioxidants such as vitamin C, vitamin E, and turmeric extract on hyperthyroidism symptoms.

Scientists discovered that treatment with vitamin C showed reduced weights in thyroid glands, less suppressed T4 and T3 levels, and less increase in total cholesterol levels[xv].

Lower cortisol

Cortisol is a stress hormone.

Higher levels of this hormone make us feel stressed out and have a major impact on our overall health.

When left unresolved, stress pose as a risk factor for numerous diseases and health conditions. Higher cortisol levels are also linked with hypothyroidism[xvi].

The thyroid works together with adrenal glands. The adrenal glands are located above your kidneys release cortisol when you encounter stress.

Too much stress can have a negative effect on thyroid and, thereby, slow the body’s metabolism.

When the function of thyroid slows down during stress, levels of T3 and T4 decrease at the same time. What’s more, the conversion of T4 to T3 may not occur at all.

Studies show that supplementation with ascorbic acid has favorable effects on blood pressure, reduced subjective stress responses, and greater salivary cortisol recovery[xvii].

Stress management in patients with hypothyroidism is particularly important if we bear in mind the disorder is associated with mood and emotional issues including depression.

Not only will cortisol regulation help manage stress and prevent these disorders, but it also prevents disturbances in thyroid hormone levels.

Adrenal glands aren’t just involved with cortisol, but vitamin C as well.

In fact, the highest concentration of vitamin C in your body accounts for adrenal glands. This micronutrient plays a major role in both the adrenal cortex and adrenal medulla, both of which are responsible for stress response.

A study whose findings were published in the American Journal of Clinical Nutrition discovered secretion of vitamin C is part of the body’s stress response[xviii].

Unresolved or chronic stress coupled with the insufficient intake of this vitamin can create deficiency which leads to adrenal stress.

It is also important to mention that one study discovered patients with hyperthyroidism had insufficient levels of vitamin C[xix].

Adrenal stress impairs the hypothalamic-pituitary-adrenal (HPA) axis.

Bearing in mind that thyroid hormone is directed or controlled by the hypothalamus and the pituitary gland, almost everything that disrupts the HPA axis is bound to have a negative impact on thyroid function as well.

In their study, German scientists confirmed that vitamin C is a vital factor for adrenal cortex and adrenal medulla[xx] (located at the center of the adrenal gland, surrounded by adrenal cortex).

Recommended daily value of vitamin C

According to the National Institutes of Health, recommended daily intake of vitamin C is[xxi]:

  • Birth to 6 months – 40mg
  • 7-12 months – 50mg
  • 1-3 years – 15mg
  • 4-8 years – 25mg
  • 9-13 years – 45mg
  • 14-18 years – 75mg (boys) and 65mg (girls)
  • Adults – 90mg (men) and 75mg (women)
  • Pregnant teens – 80mg
  • Pregnant women – 85mg
  • Breastfeeding teens – 115mg
  • Breastfeeding women – 120mg

Best sources of vitamin C

As shown above, vitamin C plays a major role in thyroid function and it is beneficial for patients who are diagnosed with either hyperthyroidism or hypothyroidism.

One of the greatest advantages of vitamin C is that we can obtain recommended daily value through the diet.

Below, you can see the list of the best sources of this micronutrient:

  • Oranges – one large orange contains 82mg of vitamin C, which is over 100% daily value (DV)
  • Red peppers – 95mg (more than 100% DV) of vitamin C in ½ cup chopped red peppers
  • Kale – one cup of kale delivers 80mg of vitamin C, which is about 134% DV
  • Brussels sprouts – you’ll find 48mg of vitamin C in ½ cooked Brussels sprouts, which accounts for 80% DV
  • Broccoli – 51mg of vitamin C is found in ½ cup cooked broccoli, or 107% DV
  • Strawberries – you’ll find 42mg or 70% DV of vitamin C in ½ cup of delicious strawberries
  • Grapefruit – 43mg or 71% DV of vitamin C is delivered in ½ cup of grapefruit
  • Guarava – one fruit delivers 125mg of vitamin C or more than 100% DV
  • Kiwi – one piece contains 64mg of vitamin C or 33% DV
  • Green peppers – you’ll find 60mg or 100% DV of vitamin C in ½ cup of chopped green peppers

If you are thinking about using vitamin C supplements to help manage hyper- or hypothyroidism you should ask your doctor first. Some thyroid supplements already contain this vitamin included.

Based on your condition and severity of symptoms, the physician will explain whether intake of vitamin C supplement would be safe or effective for you.

It’s always a good idea to discuss supplements with your doctor.

Other health benefits of vitamin C

Besides favorable impact on thyroid functioning, vitamin C has a number of health benefits including, but not limited to:

  • Stronger immune system, prevention of flu and cold
  • Stress prevention and management
  • Lower risk of stroke
  • Healthy and youthful skin
  • Improved blood flow, lowering hypertension
  • Diabetes management
  • Heart disease prevention


Back in 1928, Albert Szent-Györgyi a Hungarian biochemist isolated vitamin C or ascorbic acid which enables the body to efficiently use fats, carbohydrates, and protein.

Vitamin C is dubbed as one of the most important nutrients we can consume. Unlike some other nutrients, human bodies do not produce vitamin C, meaning we rely solely on diet or supplements to get recommended daily amounts.

Vitamin C participates in numerous processes in our body including thyroid functioning. In fact, it directly or indirectly benefits patients with hypothyroidism and hyperthyroidism.

While it is easy to obtain necessary amount through diet, some individuals prefer supplements. It’s always a good idea to seek doctor’s approval if you deal with thyroid disorders.


[i] Resch U, Helsel G, Tatzber F, Sinzinger H. Antioxidant status in thyroid dysfunction. Clinical Chemistry and Laboratory Medicine 2002 Nov;40(11):1132-4. Doi: 10.1515/CCLM.2002.198 https://www.ncbi.nlm.nih.gov/pubmed/12521231/

[ii] Zhang N, Wang L, Duan Q, et al. Metallothionein-I/II knockout mice aggravate mitochondrial superoxide production and peroxiredoxin 3 expression in thyroid after excessive iodide exposure. Oxidative Medicine and Cellular Longevity 2015;2015:267027. Doi: 10.1155/2015/267027 https://www.ncbi.nlm.nih.gov/pubmed/26101557/

[iii] Asayama K, Kato K. Oxidative muscular injury and its relevance to hyperthyroidism. Free Radical Biology and Medicine 1990;8(3):293-303 https://www.ncbi.nlm.nih.gov/pubmed/2187767/

[iv] Mancini A, Di Segni C, Raimondo S, et al. Thyroid Hormones, Oxidative Stress, and Inflammation. Mediators of Inflammation. 2016;2016:6757154. doi:10.1155/2016/6757154. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4802023/

[v] Vitamin C (ascorbic acid), University of Maryland Medical Center http://www.umm.edu/health/medical/altmed/supplement/vitamin-c-ascorbic-acid

[vi] Baskol G, Atmaca H, Tanriverdi F, et al. Oxidative stress and enzymatic antioxidant status in patients with hypothyroidism before and after treatment. Experimental and Clinical Endocrinology and Diabetes 2007 Sep;115(8):522-6. Doi: 10.1055/s-2007-981457 https://www.ncbi.nlm.nih.gov/pubmed/17853336/

[vii] Marcocci C, Leo M, Altea MA. Oxidative Stress in Graves’ Disease. European Thyroid Journal. 2012;1(2):80-87. doi:10.1159/000337976. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3821469/

[viii] Seven A, Tasan E, Inci F, et al. Biochemical evaluation of oxidative stress in propylthiouracil treated hyperthyroid patients. Effects of vitamin C supplementation. Clinical Chemistry and Laboratory Medicine 1998 Oct;36(10);767-70. Doi: 10.1515/CCLM.1998.136 https://www.ncbi.nlm.nih.gov/pubmed/9853803/

[ix] Sripad DV, Chowdary NVS, Sivaprabodh V, Shekhar R. Oxidative stress in thyroid disorders. International Journal of Current Medical and Applied Sciences December 2014, vol. 5, issue 1, 31-35 http://svimstpt.ap.nic.in/jcsr/oct-dec14_files/ambi.pdf

[x] Levothyroxine, Drugs.com https://www.drugs.com/levothyroxine.html

[xi] Jubiz W, Ramirez M. Effect of vitamin C on the absorption of levothyroxine in patients with hypothyroidism and gastritis. Journal of Clinical Endocrinology and Metabolism 2014 Jun;99(6):E1031-4. Doi: 10.1210/jc.2013-4360 https://www.ncbi.nlm.nih.gov/pubmed/24601693

[xii] Burmeister LA, Ganguli M, Dodge HH. Hypothyroidism and cognition: preliminary evidence for a specific defect in memory. Thyroid July 2004,11(12): 1177-1185. Doi: 10.1089/10507250152741037 http://online.liebertpub.com/doi/abs/10.1089/10507250152741037

[xiii] Wheeler SM, McLelland VC, Sheard E, McAndrews MP, Rovet JF. Hippocampal Functioning and Verbal Associative Memory in Adolescents with Congenital Hypothyroidism. Frontiers in Endocrinology. 2015;6:163. doi:10.3389/fendo.2015.00163. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4610202/

[xiv] Beheshti F, Karimi S, Vafaee F, et al. The effects of vitamin C on hypothyroidism-associated learning and memory impairment in juvenile rats. Metabolic Brain Disease 2017 Jun;32(3):703-715. Doi: 10.1007/s11011-017-9954-y https://www.ncbi.nlm.nih.gov/pubmed/28127705

[xv] Deshpande UR, Joseph LJ, Patwardhan UN, Samuel AM. Effect of antioxidants (vitamin C, E, and turmeric extract) on methimazole induced hypothyroidism in rats. Indian Journal of Experimental Biology 2002 Jun;40(6):735-8 https://www.ncbi.nlm.nih.gov/pubmed/12587721

[xvi] Terzidis K, Panoutsopoulos A, Mantzou A, et al. Lower early morning plasma cortisol levels are associated with thyroid autoimmunity in the elderly. European Journal of Endocrinology 2010 162, 307-313. Doi: 10.1530/EJE-09-0534 http://www.eje-online.org/content/162/2/307.full.pdf

[xvii] Brody S, Preut R, Schommer K, Schurmeyer TH. A randomized control trial of high dose ascorbic acid and reduction of blood pressure, cortisol, and subjective responses to psychological stress. Psychopharmacology 2002 Jan;159(3):319-24. Doi: 10.1007/s00213-001-0929-6 https://www.ncbi.nlm.nih.gov/pubmed/11862365

[xviii] Padayatty SJ, Doppman JL, Chang R, et al. Human adrenal glands secrete vitamin C in response to adrenocorticotrophic hormone. American Journal of Clinical Nutrition July 2007, vol. 86, no. 1, 145-149 http://ajcn.nutrition.org/content/86/1/145.long

[xix] Dubey SS, Singh RP, Udupa KN. Ascorbic acid status of hyperthyroid patients. Indian Journal of Medical Research 1977 Jun;65(6):865-70 https://www.researchgate.net/publication/22538571_Ascorbic_acid_status_of_hyperthyroid_patients

[xx] Patak P, Willenberg HS, Bornstein SR. Vitamin C is an important cofactor for both adrenal cortex and adrenal medulla. Endocrine Research 2004 Nov;30(4):871-5 https://www.ncbi.nlm.nih.gov/pubmed/15666839

[xxi] Vitamin C, National Institutes of Health https://ods.od.nih.gov/factsheets/VitaminC-Consumer/

  1. Reply
    Asfiya godil January 23, 2019 at 3:08 pm

    Hey can we eat amla if we have hypothyroidism?

  2. Reply
    Anita November 4, 2017 at 6:27 am

    Can vitamin c help hair loss too.

  3. Reply
    Zoe August 9, 2017 at 6:51 pm

    I see that you said taking vitamin c can help improve the absorption of levothyroxine. When is the best time to take vitamin c and levothyroxine? Like take them both at the same time? One after the other?

    • Reply
      Thyroid Advisor August 10, 2017 at 4:27 pm

      Hi Zoe,

      In that study, the patients took it both at the same time. They took their dosage of levothyroxine along with 120 mL of water containing 500 mg of vitamin C.

      However, be careful not to just take a general multivitamin along with levothyroxine. Some vitamins or minerals can actually cause levothyroxine absorption to be worse, such as calcium and iron. See our article here on Synthroid/Levothyroxine for more information.

  4. Reply
    Sky August 7, 2017 at 12:51 am

    I agree that cortisol and stress plays a big part in helping ‘cure’ in a sense an underactive thyroid. But I dont think, or at least im not convinced, vitamin c is as important to this as you make it out to be.

    • Reply
      Thyroid Advisor August 7, 2017 at 11:02 pm

      Hi Sky,

      Vitamin C is definitely important. This article summarized several research studies that show what happens when people do not get enough of it.

      But, I think what you’re getting at is that it’s not the only nutrient that the thyroid needs, and just getting extra Vitamin C will not solve your thyroid problems. If that’s what you’re saying, I agree with you. It’s not the most important thing in the world for your thyroid. Drinking or eating foods with extra Vitamin C will not magically fix most people’s thyroid problems. But it will likely help and begin the process of restoring thyroid balance. For that, Vitamin C is still a very much needed nutrient along with several others.

  5. Reply
    Lise August 6, 2017 at 9:57 pm

    Would orange juice be a good source of vitamin c? I didn’t see it on this list, but a lot of people, including me, probably drink a lot of orange juice everyday with breakfast.

    • Reply
      Thyroid Advisor August 7, 2017 at 10:53 pm

      Hi Lise,

      Orange juice is definitely a good source of Vitamin C. But that doesn’t mean you should be chugging the entire bottle of juice! Most orange juices contain a lot of sugars and carbohydrates, which is why some people believe it is unhealthy.

      Drinking a normal amount everyday isn’t bad. Just don’t go drinking the entire carton and be thinking it’s good for you, because it has Vitamin C… It won’t be!

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