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Thyroid issues affect around 5% of Americans and 10% of Canadians. (Beynon 2016)(Reyes Domingo 2019)(Statistics Canada 2010) While occurring in both women and men, thyroid conditions are found to be seven times more common in women. (Statistics Canada 2010)(Thyroid Foundation of Canada n.d.) Hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) are the most prevalent thyroid disorders, either producing too little or too much thyroid hormone. (Beynon 2016) Continue reading to learn about the diet and thyroid treatment strategies that may positively impact metabolism and overall well-being.

What's the thyroid gland?

The thyroid is one of the largest endocrine glands in the body. This small butterfly-shaped organ sits in front of the windpipe (trachea) in the neck and weighs 20–30 g. (Mescher 2010)

The thyroid secretes thyroid hormones, essential for regulating metabolism and body temperature, influencing growth and development, and controlling calcium levels in the blood. (Mescher 2010)

The thyroid gland is responsible for several functions, including: 

• Controlling the rate at which calories are burned and maintaining muscle function and bone health

• Producing heat and energy in the body and increasing metabolic activity

• Regulating the development and functioning of the central and peripheral nervous systems, which influences cognitive function, mood, and overall neurological health

• Regulating the heartbeat and how much blood goes into circulation 

• Regulating the speed at which food moves through the digestive tract (Bernal 2022)(Beynon 2016)(Hershman 2020)(Thyroid Foundation of Canada n.d.)

Thyroid hormone function

Normal thyroid function is maintained through the hypothalamic-pituitary-thyroid (HPAT) axis, a feedback loop involving the hypothalamus, anterior lobe of the pituitary gland, and adrenal glands. 

When thyroid hormone levels are low, the hypothalamus releases thyroid-releasing hormone (TRH) to stimulate the pituitary to release thyroid-stimulating hormone (TSH). The thyroid responds to TSH by producing and secreting more triiodothyronine (T3) and thyroxine (T4) hormones into blood circulation. 

When T4 arrives at the targeted body tissue, an iodine derivative (5-iodinase) converts T4 into its more bioactive form, T3. This regulates metabolism and body temperature, generates and absorbs glucose for energy, and increases blood output from the heart. (Beynon 2016)(Costanzo 2010)(Humphreys 2020)(Thyroid Foundation of Canada n.d.)

The HPAT axis is a feedback loop used to maintain healthy thyroid hormone levels in the body. (Stephens 2012)

Common thyroid disorders: hypothyroidism vs. hyperthyroidism

Thyroid disorders affect up to 5% of the population, with hypothyroidism and hyperthyroidism being the most common. (Beynon 2016)(Costanzo 2010)(Golden 2009)

If left untreated, they can increase the risk of adverse cardiac events and high blood pressure, elevated cholesterol, brittle bones, muscle weakness, peripheral neuropathy, cognitive impairment, and infertility. (Duyff 2000)(Gaitonde 2012)(Kravets 2016)(Reyes Domingo 2019)

Thyroid assessment may include looking at the patient’s medical history, performing a physical exam, and thyroid function testing. Treatment goals include returning thyroid levels to normal levels and preventing long-term complications. (BC Guidelines 2018)(Gaitonde 2012)(Kravets 2016)(NIDDK 2016)(NIDDK 2016)

What is hyperthyroidism?

Hyperthyroidism, a condition that affects approximately 1.3% of the population, occurs when the thyroid gland produces and secretes too much thyroid hormone. (Golden 2009)(Hollowell 2002)

Common causes of hyperthyroidism include: 

• Excessive iodine consumption 

• Grave’s disease (an autoimmune condition characterized by the destruction of thyroid tissue)

• Goiter (enlargement of the thyroid gland causing overproduction of thyroid hormones)

• Overmedicating with thyroid hormone replacement therapy

• Pituitary abnormalities, such as noncancerous (adenoma) tumors causing too much TSH 

• Thyroid nodules (cysts or nodules causing overproduction of thyroid hormone)

• Thyroiditis (inflammation of the thyroid gland causing too much then too little thyroid hormone) (Beynon 2016)(Duyff 2000)(Golden 2009)(Kravets 2016)(Thyroid Foundation of Canada n.d.)

Signs and symptoms of hyperthyroidism 

In the early stages, symptoms of hyperthyroidism may be gradual or develop suddenly. Signs and symptoms include restlessness and difficulty sleeping, weight loss, eye issues, and hot body temperature.

Common symptoms in women and men include:

• Difficulty putting on weight, despite increased appetite

• Dry and red eyes, the appearance of bulging eyes 

• Enlarged thyroid gland (goiter)

• Excessive sweating

• Fast heartbeat (palpitations)

• Frequent bowel movements or diarrhea

• Heat sensitivity

• High (systolic) blood pressure

• Mood swings, irritability, and anxiety 

• Nervous energy

• Restlessness and difficulty sleeping

• Shaky, tremors, and trembling

• Weight loss (BC Guidelines 2018)(Duyff 2000)(Kravets 2016)(NIDDK 2016)(Reyes Domingo 2019)(Vincent 2013)

Hypothyroidism and hyperthyroidism are the two most common forms of thyroid dysfunction.

What is hypothyroidism?

Hypothyroidism, affecting 4.6% of the population, results when the thyroid gland does not produce and secrete enough thyroid hormone. (Golden 2009)(Hollowell 2002)

Common causes of hypothyroidism include: 

• Certain medications, including amiodarone, interferon alpha, lithium, and interleukin-2 (NIDDK 2016)

• Congenital hypothyroidism (babies born with an underdeveloped or under-functioning thyroid)

• Hashimoto’s thyroiditis (chronic inflammation and destruction of the thyroid tissue)

• Iodine deficiency

• Pituitary abnormalities

• Radiation treatment, which can destroy thyroid cells resulting in too little thyroid hormone

• Secondary hypothyroidism (the pituitary gland fails to produce enough TSH)

• Surgical removal of part or all of the thyroid gland, resulting in too little thyroid hormone

• Thyroiditis (Beynon 2016)(Duyff 2000)(Gaitonde 2012)(Golden 2009)(NIDDK 2016)(Thyroid Foundation of Canada n.d.)

Signs and symptoms of hypothyroidism 

In the early stages, symptoms may be mild with a gradual onset. Signs and symptoms of hypothyroidism are similar in both women and men and include fatigue, weight gain, hair loss, and chilliness.

Common symptoms in women and men, include: 

• Brittle, thinning hair, and hair loss

• Constipation

• Depression

• Dry skin

• Enlarged thyroid gland (goiter)

• Erectile dysfunction

• Eyebrow thinning (outer third)

• Hoarseness and feelings of fullness in the throat 

• Hormonal issues

• Infertility

• Irregular or heavy periods

• Low libido

• Memory problems

• Muscle aches and weakness

• Sensitivity to cold

• Slow heart rate

• Tiredness or fatigue

• Weight gain (BC Guidelines 2018)(Beynon 2016)(Duyff 2000)(Gaitonde 2012)(Reyes Domingo 2019)(NIDDK 2016)(Vincent 2013)

Subclinical hypothyroidism

Subclinical (borderline) hypothyroidism affects up to 10% of the adult population. (Biondi 2019) It’s more common in women and usually presents with no symptoms.

Clinically, it’s observed with an elevated TSH and normal free T4 levels. If left untreated, 2–5% of subclinical hypothyroidism cases can progress to symptomatic hypothyroidism. (BC Guidelines 2018)(Khandelwal 2012)(Pearce 2013)

Lab testing for thyroid conditions 

Assessing thyroid function and identifying thyroid disorders require a combination of clinical evaluation and lab testing. Some of the most relevant thyroid tests are listed below.

Thyroid-stimulating hormone (TSH) test

The TSH test is often the first step in assessing thyroid function. It measures the level of TSH in the blood. High TSH levels indicate hypothyroidism, as the pituitary gland produces more TSH to stimulate an underactive thyroid. Low levels suggest hyperthyroidism, as the pituitary gland reduces TSH production in response to excessive thyroid hormone levels. (NIDDK 2023)

Free T4 test

The free T4 test measures the level of unbound T4 in the blood, which is the active form of the hormone. This test helps to confirm the diagnosis suggested by the TSH test. High free T4 levels indicate hyperthyroidism, while low levels suggest hypothyroidism. (NIDDK 2023)

Thyroid antibodies tests

These tests are used to diagnose autoimmune thyroid conditions. Elevated levels of thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) can both indicate Hashimoto’s thyroiditis. High levels of thyroid-stimulating immunoglobulin (TSI) can suggest Graves’ disease. (MedlinePlus n.d.)

Free T3

Free T3 is the measure of the most biologically active form of thyroid hormone which is free and unbound to carrier proteins. Low free T3 levels can suggest impaired conversion of T4 into T3, often seen in chronic stress or illness. This is often accompanied by elevated reverse T3 (rT3) levels. (DeGroot 2015)(Yamazaki 2021)

rT3

The rT3 test measures the level of rT3, an inactive form of T3. It can be useful in certain cases to evaluate thyroid function and metabolism. High levels may indicate non-thyroidal illness syndrome or issues with thyroid hormone conversion. (Frölich 2021)

Thyroid ultrasound

A thyroid ultrasound is an imaging test that uses sound waves to create pictures of the thyroid gland. It’s useful for detecting nodules, cysts, and structural abnormalities, and to help determine if they may become cancerous. (NIDDK 2023)

Top foods and nutrients for a healthy thyroid

When formulating patient treatment plans, diet is an important factor to consider. Thyroid health can be supported by eliminating specific foods and encouraging a quality diet rich in whole foods.

Various whole, unprocessed foods contain thyroid-friendly nutrients, including:

• Fruits and vegetables (Kaličanin 2020)

• Gluten-free grains and pseudograins (e.g., oats, brown rice, quinoa) (Kravets 2016)(National Institutes of Health 2020)

• Healthy fats (e.g., plant oils, extra virgin olive oil) (Kaličanin 2020)(Pang 2021)

• Lean meats, fish, and eggs (Kaličanin 2020)(National Institutes of Health 2020)(National Institutes of Health 2020)(National Institutes of Health 2020)

• Nuts and seeds (excluding peanuts) (Kaličanin 2020)(National Institutes of Health 2020)(National Institutes of Health 2020)

Thyroid-friendly foods include lean meats, fish and seafood, eggs, a variety of fruits and vegetables, legumes, nuts and seeds, and healthy fats.

Encourage foods rich in zinc, selenium, and iodine

Specific minerals are needed to maintain thyroid gland function and essential for overall thyroid health. (Ambooken 2013)(Kralik 1996)(Negro 2008)(Ventura 2017)(Wu 2015)(Zimmermann 2015)  Zinc, selenium, and iodine can be obtained in the diet by consuming thyroid-friendly foods, including: 

• Zinc-rich foods: oysters, beef, crab, lobster, baked beans, pumpkin seeds, cashews, almonds, kidney beans, eggs, green peas, dark chocolate (National Institutes of Health 2020)

• Selenium-rich foods: brazil nuts, tuna, halibut, sardines, beef, turkey, chicken,brown rice, eggs, baked beans, lentils, cashews, green peas (National Institutes of Health 2020)

• Iodine-rich foods: seaweed, dulse, kelp, cod, yogurt, oysters, eggs, liver, cheddar cheese, shrimp, iodine enriched breads and salt (National Institutes of Health 2020)

The bottom line

The thyroid gland is a small but mighty organ, influencing the entire body. Understanding lab test options for thyroid assessment is key to making an accurate diagnosis. Once a clear diagnosis is established, considering dietary intervention strategies is a great way to support patient thyroid health overall.