The thyroid gland plays a crucial role in regulating various body processes, particularly those related to metabolic function. Maintaining optimal thyroid function and balanced levels of its main hormones, triiodothyronine (T3) and thyroxine (T4), is essential for overall health. Thyroid dysfunction is relatively common and can arise from conditions like thyroiditis and hypothyroidism.

In the United States, approximately 10% of adults are estimated to be affected by hypothyroidism, and this percentage might be even higher in older populations. The most prevalent form of hypothyroidism is Hashimoto's thyroiditis, an autoimmune condition that affects about one to two percent of the US population, primarily women. In Hashimoto's, an aberrant immune response disrupts the production of thyroid hormones.

The functional medicine approach can offer valuable support in restoring thyroid hormone balance and promoting thyroid health. It begins with understanding the underlying factors that might be causing the imbalance (like diet, stress, environmental toxins, etc.). By addressing these root causes, functional medicine aims to provide personalized and comprehensive care to individuals experiencing thyroid issues.

Among the different factors that may negatively affect thyroid health, endocrine disruptors can have a potentially major impact on the function of this gland. A 2023 systematic review of 237 observational studies investigated the association between endocrine-disrupting chemical (EDC) exposure and risk of endocrine-related malignancies. The review found that the most tumorigenic EDC groups were phthalates, heavy metals, particulate matter, and pesticides, and that the thyroid was the endocrine organ that presented the highest cancer risk after EDC exposure.

A 2021 investigation on EDCs, which are often found in foods, food packaging, water, and personal care products, indicated that EDCs such as bisphenol A (BPA), phthalates, and flame retardant compounds, including polychlorinated biphenyls (PCBs), can interfere with thyroid gland functioning and thyroid hormone transport through multiple mechanisms. Specific to BPAs, in vitro and in vivo studies report that antagonism with thyroid receptors, influencing gene expression at the thyroid and pituitary levels, and interruption of thyroid transport proteins are among the mechanisms leading to thyroid dysfunction. An additional study specific to phthalate exposure suggested that this toxicant may influence thyroid hormone levels through induced oxidative or nitrosative stress. Observational studies have also noted a higher prevalence of autoimmune thyroid diseases in people living in polluted areas, near petrochemical plants, and in areas contaminated with organochlorine pesticides or PCBs.

Other factors that may impact thyroid hormone balance include stress as well as chronic inflammation. While the mechanisms have not been fully identified, impaired regulation of oxidative stress and inflammation, for example, characterizes the progression of subclinical hypothyroidism, which increases the risk for cardiovascular diseases, including hypertension. Specific to thyroid hormone changes due to psychological stress, a 2020 systematic review of 10 observational studies examined the association between thyroid function and posttraumatic stress disorder (PTSD). The meta-analysis showed higher levels of free T3 in patients with combat-related PTSD compared with controls, with no differences in thyroid-stimulating hormone (TSH), free T4, or total T4 between groups, suggesting that PTSD may contribute to changes in thyroid function.

SUBCLINICAL HYPOTHYROIDISM: THE CONTROVERSY & TESTING CHALLENGES

Experts continue to make differing recommendations regarding the treatment of subclinical hypothyroidism and whether or not to give exogenous thyroid hormones. With this condition, TSH levels are elevated, while circulating thyroid hormone levels are normal. Some reports indicate that 90% of patients with subclinical hypothyroidism have TSH levels between 4 and 10 mIU/L15 while other reports define the thyroid condition based on a TSH screening level over 4.5 mIU/L. The upper limit of the TSH range for diagnosis and levothyroxine treatment is debated, as well as the effectiveness of conventional thyroid hormone therapy in mild hypothyroidism. Regardless of the mentioned controversy, some functional medicine strategies may help with low-functioning thyroid issues by using low-risk diet and lifestyle treatments that may improve thyroid function by addressing the root of the issue. In addition to a comprehensive thyroid evaluation, consideration of an individual patient’s specific disease, lifestyle, comorbidities, and other pertinent factors helps to create a valuable overview for potential treatment direction.

Balancing Thyroid Hormone: Nutrition, Gut Health, And Liver Function

Functional medicine recognizes that illness does not occur in isolation. This is why we organize a patient’s clinical imbalances in the following biological systems, called nodes: defense and repair, energy, biotransformation and elimination, transport, communication, structural integrity, and assimilation. Addressing toxicant exposures, systemic inflammation, and chronic stress are all approaches to enhancing thyroid health.

We also consider the following:

• Factors that inhibit proper production of thyroid hormones.

• Factors that increase conversion of T4 to RT3.

• Factors that contribute to the proper production of thyroid hormones.

• Factors that increase conversion of T4 to T3.

• Factors that improve cellular sensitivity to thyroid hormones.

Personalized interventions that focus on biotransformation, anti-inflammatory diets, specific nutrients, and optimizing gut and liver health are important considerations for restoring thyroid hormone balance. Adequate intake and availability of micronutrients such as iodine and iron are crucial for thyroid hormone synthesis, while selenium and zinc are needed for the conversion of T4 to T3, which takes place primarily in the liver but also in other organs such as the intestines as well as intracellularly. In addition, supplements used as complementary treatments may positively impact thyroid functioning. For example, ashwagandha has been used to help address thyroid dysfunctions. Recently, a 2018 pilot study compared the efficacy and safety of ashwagandha root extract in subclinical hypothyroid patients to a placebo. The treatment group received 600 mg of the root extract per day for eight weeks. Results showed an improved serum TSH and T4 at the end of treatment compared to placebo, with few mild and temporary adverse effects.

Gut health and a balanced microbial landscape benefit many system processes in the body, including thyroid homeostasis. Dysbiosis and intestinal autoimmune diseases have been reported concurrently with autoimmune thyroid diseases. To further explore the relationship between gut and thyroid health, a 2020 clinical trial investigated the effect of synbiotic supplementation (which combines pre and probiotic ingredients) on thyroid function. Patients with hypothyroidism on levothyroxine either received 500 mg/day of the synbiotic or a placebo for eight weeks. After treatment, results indicated a beneficial effect, with TSH concentration, levothyroxine dose, and fatigue severity scale scores significantly decreased in the synbiotic group compared to placebo.

The thyroid-liver axis is another illustration of the system-wide impact of thyroid health. In this complex relationship, the liver plays an important role in thyroid hormone activation, transport, and metabolism, and thyroid hormones impact hepatocyte activity and liver metabolism. Therefore, an imbalance in thyroid hormones may consequently influence liver structure and function.