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Hypothyroidism is a prevalent endocrine disorder characterized by an underactive thyroid gland, leading to insufficient production of thyroid hormones. Based on data from the National Health and Nutrition Examination Survey (NHANES) conducted by the Centers for Disease Control and Prevention (CDC), the prevalence rate of hypothyroidism grew from 9.6% in 2009 to 14.4% in 2019 in the United States. (Wyne 2022)

According to the American Academy of Family Physicians (AAFP), the primary screening test for thyroid dysfunction is the measurement of serum thyroid-stimulating hormone (TSH). (American Thyroid Association 2024)(Vasileiou 2020) Although assessment guidelines often focus on TSH levels alone for diagnosis and management, a case can be made for whole person care that incorporates comprehensive lab assessment along with patient symptoms and underlying factors that may be affecting thyroid function.

Understanding hypothyroidism

Hypothyroidism can be classified into primary, secondary, and tertiary forms. Primary hypothyroidism is the most common and occurs due to thyroid gland dysfunction. Secondary hypothyroidism is characterized by insufficient TSH production by the pituitary gland, leading to reduced thyroid hormone synthesis and subsequent hypothyroid symptoms. Tertiary hypothyroidism is characterized by the insufficient production of thyrotropin-releasing hormone (TRH) by the hypothalamus, leading to a cascade of hormonal deficiencies that ultimately result in reduced thyroid function.

It’s worth mentioning that autoimmune conditions, particularly Hashimoto's thyroiditis (HT), are the leading cause of hypothyroidism. (Mikulska 2022)(Patil 2024) The prevalence of HT, which is rising globally, varies by region and socioeconomic level and ranges from 4.8–25.8% in women and 0.9–7.9% in men. (Hu 2022) These statistics highlight how disproportionately women are affected by hypothyroidism, with prevalence rates up to eight times higher than in men. (Chiovato 2019) Furthermore, hormonal fluctuations during menstruation, (Jacobson 2018) pregnancy, (Singh 2023) and menopause (Xu 2023) can significantly influence thyroid function in women.

In the United States, the rates of hypothyroidism–a condition more common in women–grew from 9.6% in 2009 to 14.4% in 2019. 

Assessment and diagnosis of hypothyroidism

Measurement of serum TSH levels is the primary screening test for thyroid dysfunction. According to the AAFP guidelines, TSH elevation is sufficient for diagnosing hypothyroidism. The reference range for normal TSH varies from lab to lab, but the American Thyroid Association suggests that the standard reference range for low-end normal TSH is 0.4 mIU/L, with the upper-end normal range ranging from 4–4.5 mIU/L. (American Thyroid Association 2020) A thyroxine (T4) level is often drawn in reflex to a high TSH to distinguish clinical (low FT4) from subclinical (normal FT4) hypothyroidism.

The limitations of TSH-only testing

Relying solely on TSH testing can miss subclinical hypothyroidism and other thyroid dysfunctions. TSH levels may appear normal even when patients exhibit symptoms of hypothyroidism, (Ling 2018) underscoring the need for a more comprehensive assessment. Furthermore, TSH testing alone doesn't account for factors like nutrient deficiencies, (Krishnamurthy 2021) adrenal health, (Rizzo 2020) or environmental toxins, (Egalini 2022) which can all impact thyroid function.

Benefits of a whole person care approach to thyroid health

Functional and integrative medicine prioritizes a whole person care approach, addressing the root causes of thyroid dysfunction rather than just the symptoms. This method can lead to effective and sustainable health outcomes by considering dietary, lifestyle, and environmental factors alongside traditional medical assessments.

This might include assessing the classic symptoms associated with hypothyroidism, such as fatigue, weight gain, cold intolerance, dry skin, and hair loss, as well as less specific but common symptoms like bradycardia, hoarseness, and menstrual irregularities that often also present in these patients. The latter may require additional differential evaluation and testing to identify the root cause. When hypothyroidism is properly treated, often those related symptoms will also resolve or improve.

(NIDDK 2022)(Wilson 2021)

Beyond TSH: Comprehensive thyroid testing

A comprehensive thyroid assessment includes evaluating the following biomarkers in addition to TSH. Interpreting these biomarkers requires an understanding of their interplay and how they correlate with patient symptoms. (Soh 2022) It’s important to emphasize that correlating lab results with clinical presentation, including symptoms such as fatigue, weight gain, and cold intolerance, can provide critical context for lab findings, leading to a more accurate diagnosis and effective treatment plan.

Total thyroxine and triiodothyronine

Total thyroxine (T4) and total triiodothyronine (T3) levels measure the total levels of T4 and T3 hormones, including both bound and unbound forms. These can be helpful in certain clinical scenarios to optimize thyroid function. (Soh 2022)

Free thyroxine and triiodothyronine

Unlike total levels, free T4 (FT4) and free T3 (FT3) tests measure only the amount of unbound T4 and T3 in the bloodstream, respectively. This offers a more accurate assessment of the free or more bioavailable form of the hormones. (Soh 2022)

Reverse T3

Reverse T3 (rT3) measures this less active form of T3 hormone. This test is especially useful in assessing thyroid hormone metabolism and evaluating thyroid dysfunction in cases of high stress and adrenal involvement. (Van Uytfanghe 2023)

T4 and T3 uptake

Measuring T3 and T4 uptake helps assess the availability of thyroid hormone binding sites and provides a clearer picture of hormone activity in the body. T4 uptake is particularly useful for calculating the free thyroxine index (FTI), which remains constant despite variations in binding proteins, aiding in accurate diagnosis of thyroid conditions. (Pantalone 2015)(Van Uytfanghe 2023)

Autoimmune testing

Autoimmune testing involves comprehensive testing for various thyroid antibodies, including:

• Thyroid peroxidase antibodies (TPOAb): These antibodies target the thyroid peroxidase enzyme impacting the production of thyroid hormone and are commonly elevated in Hashimoto’s thyroiditis. (Soh 2022)

• Thyroglobulin antibodies (TgAb): These antibodies target thyroglobulin, a protein involved in thyroid hormone synthesis, and are associated with Hashimoto's hypothyroidism. (Soh 2022)

• Thyroid-stimulating immunoglobulin (TSI): TSI measures the presence of TSH receptor antibodies, making it a useful marker for diagnosing Grave’s disease. (Soh 2022)

A comprehensive assessment combining laboratory and functional testing helps clinicians gain insights into contributing factors impacting thyroid health and overall well-being.

Additional factors affecting thyroid function

The assessment of root cause influences on thyroid health should consider lifestyle and environmental factors, including nutrition, stress, and environmental considerations.

Nutrition

Nutritional deficiencies can significantly impact thyroid health. Ensuring adequate intake of these nutrients is essential for optimal thyroid function:

• Selenium: Selenium is crucial for the production of thyroid hormones and the conversion of T4 to the more active T3 hormone. Selenium deficiency can lead to impaired thyroid hormone metabolism, increased oxidative stress, and a heightened risk of autoimmune thyroid diseases. (Gorini 2021)

• Iron: Iron is essential for thyroid hormone synthesis and metabolism. Iron deficiency can lead to impaired thyroid hormone production by reducing the activity of the thyroid peroxidase enzyme and diminishing the conversion of T4 to T3, resulting in hypothyroidism and exacerbating its symptoms. Iron deficiency also influences the risk of thyroid autoimmunity, raising the likelihood of conditions such as Hashimoto's thyroiditis. (Garofalo 2023)

• Vitamin B12: B12 deficiency can impair the conversion of T4 to T3, thereby reducing the overall activity of thyroid hormones. (Krishnamurthy 2021)

• Zinc: Zinc plays a role in thyroid hormone synthesis and regulation, as well as immune activity. Zinc deficiency can impair thyroid function, reduce the conversion of T4 to T3, and increase the risk of hypothyroidism and autoimmune thyroid disease. (Krishnamurthy 2021)

• Vitamin D: Adequate vitamin D levels are important for thyroid health, as vitamin D deficiency has been associated with autoimmune thyroid disorders and impaired thyroid function. (Zhao 2021)

The gut and microbiome

Gut health and the microbiome play a crucial role in thyroid function. A healthy gut ensures the efficient absorption of essential nutrients that are vital for thyroid hormone production. Disruptions in the gut microbiome as well as increased intestinal permeability (leaky gut) can trigger immune responses that attack the thyroid, exacerbating autoimmune thyroid conditions like Hashimoto's thyroiditis. Additionally, an imbalanced microbiome can increase systemic inflammation and immune dysregulation, negatively impacting thyroid function. (Bargiel 2021)

Adrenal health

Chronic stress and adrenal dysfunction can impair thyroid function through multiple mechanisms. This includes suppressing hormone production, impairing the conversion of thyroid hormones, triggering autoimmune responses, and disrupting gut health and nutrient absorption. Managing stress through lifestyle changes and other interventions is essential for maintaining thyroid health and overall well-being. (Kyriacou 2023)

Environmental toxins

Exposure to environmental toxins such as heavy metals (e.g., mercury and lead) and endocrine disruptors (e.g., bisphenol A (BPA) and phthalates) can significantly impair thyroid function. (Calsolaro 2021) These toxins can interfere with thyroid hormone synthesis, disrupt hormone signaling, and contribute to thyroid gland inflammation. Identifying sources of these toxins and minimizing exposure is an essential component of integrative thyroid care.

Utilizing comprehensive laboratory assessment

Laboratory testing provides essential information about thyroid function and autoimmune activity. Furthermore, combining functional testing with traditional laboratory tests helps clinicians gain insight into contributing factors that can impact thyroid health and overall well-being.

When assessing thyroid function, clinicians may wish to consider the following thyroid lab test panels, combining advanced markers with traditional tests.

1. Start with a comprehensive thyroid panel test

This includes a basic TSH and T4 (free and total T4), along with free T3, total T3, reverse T3, and thyroid antibodies (e.g. TgAb, TPOAb). These tests provide a broad-spectrum analysis of thyroid function.

2. Add on functional medicine labs

Focus on potential root causes of hypothyroidism including micronutrients and gut health, which might influence thyroid function.

• Nutrition testing: Evaluate nutritional status using foundational nutritional laboratory testing for various vitamins and minerals and/or more advanced functional nutrition testing such as urinary organic acids.

• GI/microbiome stool tests: Assess imbalances in the gut microbiome and digestive function that may contribute to hormonal and inflammatory dysfunction and therefore impact the physiologic function and metabolic activity of thyroid hormones. (Bargiel 2021)(De Freitas Cayres 2021)

• Environmental/toxin panels: These panels evaluate exposure to potential thyroid disruptors like heavy metals and endocrine-disrupting chemicals. (Egalini 2022)

The bottom line

Incorporating a comprehensive assessment for hypothyroidism beyond TSH can significantly improve patient outcomes. By embracing a functional and integrative approach, clinicians can address the root causes of thyroid dysfunction and provide more personalized care.