Table of Contents
- 1 Introduction
- 2 Vitamin C steps in to combat oxidative stress
- 3 Enhanced hormone absorption
- 4 Recommended daily value of vitamin C
- 5 Other health benefits of vitamin C
- 6 Conclusion
- 7 References
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.
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.
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.
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.
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].
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].
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.
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[xxi] Vitamin C, National Institutes of Health https://ods.od.nih.gov/factsheets/VitaminC-Consumer/