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Hypothyroidism is a condition in which the thyroid gland fails to produce sufficient thyroid hormones. Hypothyroidism can be classified into various categories. Among these is subclinical hypothyroidism, which is a milder form in which thyroid hormone levels are normal, but thyroid-stimulating hormone (TSH) levels are elevated. While there are no noticeable symptoms, subclinical hypothyroidism may progress to full-blown hypothyroidism. Autoimmunity is the most common cause of hypothyroidism (i.e., Hashimoto’s thyroiditis); however, the condition may be due to other causes such as nutrient deficiencies.

Thyroid hormone is produced through the hypothalamus-thyroid-pituitary (HTP) axis. Issues anywhere along this pathway can impair thyroid hormone production, including decreased thyroid hormone synthesis, impaired thyroxine (T4) to triiodothyronine (T3) conversion, and decreased receptor sensitivity. (Salvatore 2022) Nutritional status plays a significant role in these steps and therefore assessing and optimizing nutrition can be critical to improving thyroid function.

A holistic approach to treating thyroid conditions can offer several advantages over standard hormone replacement therapy alone. While hormone replacement is effective at managing symptoms and normalizing hormone levels, a whole person care approach addresses the broader range of factors that may be underlying thyroid dysfunction. This holistic approach provides a more comprehensive strategy by addressing dietary, lifestyle, and environmental factors that impact thyroid health and lead to improved management of thyroid function. (Matlock 2023)

Nutrition and thyroid health

Many nutrients play a crucial role in maintaining optimal thyroid function. These nutrients support thyroid hormone production, peripheral conversion and activation, and receptor activity and cellular function. Clinicians can ensure adequate intake of these nutrients by conducting a comprehensive assessment and designing protocols that promote optimal thyroid function and ensure proper metabolism, energy levels, and growth and development throughout the lifecycle.

Proper nutrition is vital for thyroid function. It provides the necessary nutrients that support hormone synthesis and regulation, ensuring the thyroid gland operates efficiently. 

Iodine

Iodine plays a critical role in the synthesis of thyroid hormones as it's needed to produce T3 and T4. (Knezevic 2020) Food sources of iodine include seafood, eggs, iodized salt, and milk products. (NIH n.d) Ingested iodide is absorbed in the stomach and small intestine and transported in plasma to the thyroid gland. From there, it's accumulated by the sodium-iodide-symporter (NIS), oxidized, and incorporated into thyroglobulin, a thyroid hormone precursor. (Köhrle 2023) (Rousset 2015)

While iodine is a necessary component of thyroid hormone, excess intake in susceptible individuals may lead to conditions such as hyperthyroidism, hypothyroidism, goiter, and thyroid autoimmunity. (Farebrother 2019)

Tyrosine

Tyrosine is an amino acid that's used as a building block for thyroid hormones and is obtained from dietary protein. (Polak 2013) When insufficient amounts are ingested, it can also be synthesized from an essential amino acid, phenylalanine, that can only be obtained from diet. (Leonard 2004) (Mount Sinai n.d) A balanced diet that includes sufficient protein ensures the availability of tyrosine and tyrosine precursors for thyroid hormone synthesis. (Polak 2013)

Iron

Iron deficiency impairs the metabolism of thyroid hormone through various mechanisms, resulting in lower levels of circulating T3 and T4. (Eftekhari 2005) One way this occurs is through reduced thyroid peroxidase (TPO) activity caused by iron deficiency. (Hess 2002) TPO is a hemoprotein that contains iron in the active center and requires the binding of heme in order to function. (Knezevic 2020) (Rayman 2019) Therefore, sufficient iron supply is necessary for effective thyroid hormone synthesis (Triggiani 2009)

Iron deficiency also leads to decreased peripheral conversion of T4 to T3. (Garofalo 2023) Several studies have indicated that the decreased oxygen-carrying capacity associated with iron deficiency hinders the peripheral conversion of T4 into the active T3 thyroid hormone. (Galton 1972) (Surks 1969)

Given that symptoms of iron deficiency, such as fatigue and hair loss, can overlap with those of hypothyroidism, it's important to rule out iron deficiency as a potential underlying cause of hypothyroidism. (NIH 2022) (NHS 2024) Furthermore, iron serves as a cofactor for the antioxidant enzyme catalase, thus contributing to overall thyroid health. (Anwar 2024)

Zinc and copper

Zinc is essential for thyroid hormone metabolism because it plays a role in various stages of thyroid hormone production and overall health. Food sources of zinc include animal-based products, such as meat, seafood, and dairy, and plant sources, such as pumpkin seeds and lentils. (NIH n.d) Zinc deficiency inhibits thyrotropin-releasing hormone, which normally stimulates the anterior pituitary gland to release TSH. As a result, low levels of zinc lead to decreased serum levels of TSH. (Krishnamurthy 2021) Additionally, zinc is needed for the conversion of T4 to active T3. (Knezevic 2020) Zinc also plays a role in sensitivity to thyroid hormone as it's important for T3 receptor activation. (Baltaci 2019) (Benvenga 2020) Lastly, zinc is a critical component of the antioxidant enzyme superoxide dismutase, so it can help protect the thyroid against reactive oxygen species. (Altobelli 2020) (Triggiani 2009)

Copper is also important for thyroid hormone synthesis as it plays a role in the production of T4. (Knezevic 2020) Tyrosinase is an enzyme that synthesizes tyrosine, acts as a building block for thyroglobulin, and is dependent on copper for activation. Copper deficiency limits the availability of tyrosine for thyroid hormone synthesis. (Krishnamurthy 2021) Copper is also a critical component of superoxide dismutase and therefore plays a crucial role in protecting the thyroid from free radical damage. (Triggiani 2009) Part of managing copper status involves the assessment of the zinc-to-copper ratio.

Selenium

In the thyroid, selenium is essential for both thyroid hormone regulation and antioxidant activity. (Ventura 2017) Selenium food sources include seafood, meat, eggs, lentils, and Brazil nuts. (NIH n.d) Selenium supports the thyroid gland’s ability to produce and convert thyroid hormones effectively. Being a cofactor of the deiodinases, selenium is needed for the conversion of T4 into T3, the active thyroid hormone, and also helps in inactivating thyroid hormones by converting T4 into reverse T3 or T3 into diiodothyronine (T2). (Benvenga 2020) (Triggiani 2009) (Yamauchi 2021)

Furthermore, selenium is a critical component of various selenoproteins found in the thyroid, including glutathione peroxidase and thioredoxin reductase, which help protect the thyroid gland from the hydrogen peroxide and reactive oxygen species produced during thyroid hormone synthesis. (Köhrle 2023) (Rayman 2012) (Triggiani 2009) (Ventura 2017)

Vitamin D

Maintaining adequate vitamin D levels is crucial because it supports thyroid health and hormone production in various ways. Vitamin D is important for the regulation of our immune system as vitamin D deficiency is associated with thyroid autoimmunity and impaired thyroid function. (Kivity 2011) (Knezevic 2020) Several studies have found a relationship between vitamin D deficiency and elevated levels of thyroid peroxidase antibodies (anti-TPO). (Krishnamurthy 2021) Vitamin D also affects the peripheral conversion of thyroid hormone, as it modulates deiodinase expression at the thyroid and other organs involved in the peripheral conversion of T4 into T3. (Vassalle 2021)

Vitamin D may also be important in thyroid hormone production at a central level. (Leko 2023) (Vassalle 2021) Research demonstrates that higher vitamin D levels are associated with lower TSH levels, independent of thyroid hormone levels. (Zhang 2014) Furthermore, vitamin D is important for thyroid function, as vitamin D deficiency has been associated with impaired cell receptor sensitivity to thyroid hormones. (Zhou 2023)

Vitamin A

Vitamin A is also crucial for the production, conversion, and cellular sensitivity to thyroid hormones. Vitamin A is involved in thyroid hormone synthesis in two distinct ways. Vitamin A deficiency can impair the synthesis of thyroglobulin, a thyroid hormone precursor, and reduce the uptake of iodine by the thyroid. (Wolf 2002) Furthermore, vitamin A is involved in the peripheral conversion of thyroid hormone, as vitamin A has been shown to enhance T4 to T3 conversion. (Zimmermann 2007) Vitamin A also improves cellular sensitivity to thyroid hormones as vitamin A contributes to the establishment of intracellular receptors for T3. (Farasati 2023)

While vitamin A is needed for healthy thyroid function, a balanced approach is important. Excessive amounts have been shown to have the opposite effect and impair thyroid function (Far 2023)

Magnesium

Magnesium is important because it has anti-inflammatory effects, and magnesium deficiency is associated with autoimmune thyroid disorders. Several studies have found a correlation between higher magnesium intake and lower levels of inflammatory markers. (Kim 2010) (Song 2007) Research also demonstrates that patients with severe magnesium deficiency were 4–5 times more likely to have subclinical or overt hypothyroidism compared with those with normal magnesium levels. (Wang 2018) Furthermore, magnesium plays a role in thyroid function and oxidative metabolism, with some studies suggesting that magnesium can improve thyroid function and reduce inflammation associated with thyroid disease. (Wang 2018)

B vitamins

Several B vitamins appear to also be involved in thyroid health and hormone production. (Dahiya 2022) (Krishnamurthy 2021) Deficiencies of vitamins B2, B6, B9 (folate), and B12 negatively affect thyroid functioning. (Krishnamurthy 2021) For example, folate deficiency was associated with a higher risk of elevated TSH levels and hypothyroidism in patients with type 2 diabetes. (Lin 2023) Research demonstrates that vitamin B6 deficiency can also lead to hypothyroidism resulting from reduced TRH synthesis in the hypothalamus. The reversal of vitamin B6 deficiency, however, has resulted in the normalization of thyroid hormone levels. (Dakshinamurti 1990) Furthermore, vitamin B3 can also improve thyroid function. (Niacin n.d)

While B vitamins are important for thyroid function, it's important to note that biotin supplementation can lead to inaccurate measurements of thyroid hormones. It’s therefore recommended to discontinue biotin supplementation for at least 3–5 days before getting thyroid testing. (ATA 2018) (ATA 2022)

Antioxidants

Antioxidants play a crucial role in maintaining thyroid health by protecting thyroid cells from oxidative stress and damage. The thyroid gland is particularly susceptible to oxidative damage due to its high metabolic activity and the production of reactive oxygen species during hormone synthesis.

Antioxidants, such as selenium, vitamin A, vitamin E, and vitamin C, neutralize these harmful free radicals, thereby preserving the function and integrity of thyroid cells. This is particularly important in hypothyroidism, as the condition decreases the activity of the antioxidant system, leading to an increase in reactive oxygen species. Other notable nutrients that promote antioxidant mechanisms include polyunsaturated fatty acids (PUFAs) and monounsaturated fatty acids (MUFAs), curcumin, and resveratrol as well as factors that favorably impact the microbiome. (Macvanin 2023)

Adequate antioxidant levels help ensure proper thyroid hormone production and support overall gland function, reducing the risk of thyroid disorders and promoting hormonal balance.

Apps can help track dietary intake and provide nutritional analysis.

Nutrition assessment

There are numerous ways healthcare providers can assess a patient’s diet. Assessment may begin with a dietary recall in which the patient is asked to recall and describe all the foods and beverages they consumed over the past 24 hours. Other methods of gathering more insight into diet can include using a Food Frequency Questionnaire (FFQ), which is a structured questionnaire that asks about the frequency and portion size of various foods consumed over a specified time period. FFQs are often used to assess long-term dietary patterns. Food diaries or journals, in which the patient keeps a detailed log of their daily food and beverage intake over a period of time, can also be useful. Some patients may prefer using apps such as MyFitness Pal or Cronometer for tracking dietary intake. These apps can be very valuable for providing nutritional analysis.

Furthermore, biochemical tests, such as blood tests or other laboratory analyses, can help measure levels of specific nutrients or biomarkers that indicate dietary intake and nutritional status.

Lab testing strategies

Thorough lab testing of thyroid markers such as TSH, free T3, free T4, and thyroid antibodies can help provide a comprehensive picture of thyroid function and identify conditions such as Hashimoto’s thyroiditis. While thyroid panels are crucial for diagnosis, lab tests assessing nutrient status can help identify contributing factors and provide guidance for optimizing treatment plans. For example, these tests can include:

• Complete blood count (CBC) with serum iron and other related tests such as ferritin, transferrin saturation, total iron-binding capacity (TIBC) (Singh 2023)

• Serum folate and B12, along with organic acids homocysteine and methylmalonic acid (Kundrapu 2018) (Kesari 2023)

• Vitamin D (Kesari 2023)

• Vitamin A and tocopherols (vitamin E) (Kesari 2023)

• Minerals including red blood cell (RBC) magnesium, selenium, and zinc (Kesari 2023)

• Other B vitamins, including thiamine, riboflavin, niacin, and pyridoxine (Kesari 2023)

• Omega-3 index and arachidonic acid to eicosapentaenoic acid (AA/EPA) ratio (Dolan 2018)

Organic acids test

Organic acid testing can help assess nutritional deficiencies by measuring the concentrations of various organic acids in the urine, which reflect metabolic processes and nutrient utilization. (Rogers 2006) Elevated or reduced levels of specific organic acids can indicate deficiencies in vitamins, minerals, amino acids, and fatty acids. By analyzing these metabolic byproducts, healthcare providers can gain insights into nutrient imbalances and can help guide appropriate dietary or supplementation strategies to improve thyroid health.

Other lab tests to consider

Apart from nutritional status, other lab tests can help assess other factors influencing thyroid health. For example, cortisol testing can help identify adrenal causes or chronic stress that may be inhibiting thyroid function. Environmental toxin panels can help identify heavy metal accumulation that can have a negative effect on thyroid function. Microbiome testing can help identify imbalances in the gut microbiome that also affect thyroid hormone production and immune regulation.

Genetic testing can also be useful as genetic factors contribute to a majority of autoimmune thyroid diseases. (Wiersinga 2016) Genetic profiles might be helpful in understanding susceptibility to developing thyroid disease. Common genetic factors include major histocompatibility complex genes (HLA class I and II), genes associated with thyroid peroxidase antibody synthesis (BACH2, TPO), and genes involved in the regulation of immune response (CD40, CTLA4, PD1). (Weetman 2020) (Wiersinga 2016)

The bottom line

Nutritional assessment plays a crucial role in maintaining thyroid health, as the thyroid gland relies on a variety of nutrients to function optimally. An imbalance or deficiency in these nutrients can disrupt thyroid function, leading to conditions like hypothyroidism. By evaluating nutritional status, healthcare professionals can identify deficiencies or imbalances and recommend appropriate dietary adjustments to help optimize thyroid health and overall well-being.