What Does the Thyroid Do?

As part of the endocrine system, a system in charge of controlling hormone production, the thyroid’s main role is producing and releasing specific hormones, regulating how the body transforms food into energy, and regulating the speed of metabolism. The thyroid produces and releases two specific hormones: T3 and T4.

T4: The primary hormone your thyroid makes and releases–it is converted into T3 to have a greater effect on metabolism.

T3: T3 is the active hormone that tells your cells how much energy to produce. Think of your thyroid as your body’s thermostat–it regulates how quickly or slowly your body uses energy.

Like other systems in the body, the thyroid doesn’t work alone! The hypothalamus, located in the brain, secretes TRH (thyroid-releasing hormone), which in turn sparks the pituitary gland to release TSH (thyroid-stimulating hormone). From there, TSH signals to thyroid cells to release T4 and T3.

This communication system is called the HPT axis, or the hypothalamus-pituitary-thyroid axis. Learn more about the hypothalamus and pituitary gland and the other endocrine systems they support, such as the HPA axis (hypothalamus-pituitary-adrenal) and HPO axis (hypothalamus-pituitary-ovary), by reading my previous blog: “The Brain, the Endocrine System, and the Gut Microbiome: How They Work Together.”

Thyroid Stressors

Chronic stress can suppress thyroid function.
Poor adrenal health influences thyroid hormone conversion.
Sex hormones (estrogen and progesterone) interact with thyroid hormones.
Thyroid dysfunction can affect fertility, menstrual cycles, PMS, and menopause.

Remember, everything is connected—rarely is the thyroid the only issue. There is a constant feedback loop between:

Brain → Pituitary → Thyroid → Adrenals → Ovaries

Hypothyroid versus Hyperthyroid

Hypothyroid (underactive thyroid):

When the thyroid gland doesn’t make enough of the thyroid hormone, it can lead to a condition called underactive thyroid, or hypothyroidism.

Symptoms of hypothyroidism:

Tiredness
Weight gain
Puffy face
Coarse skin and hair
Menstrual cycles that are very heavy or irregular
Thinning hair
Slowed heart rate
Depression
Brain fog

Hyperthyroid (overactive thyroid)

As the opposite of hypothyroidism, hyperthyroidism occurs when the thyroid makes too much of the thyroid hormone.

Symptoms of hyperthyroidism:

Weight loss without trying
Fast and/or irregular heart rate
Increased hunger
Nervousness or anxiety
Sweating
Changes in menstrual cycles
Sleep issues
Changes in bowel movements, especially an increase in frequency

Ways to Support the Thyroid

Prioritize protein
- Try my Garlic Sesame Chicken Zucchini Bowl recipe!

Manage stress
- A 2024 study researching the association of stress and the thyroid concluded that stress and stressful events can affect the HPT axis. Specifically, stress increases thyroid hormone secretion but decreases TSH, potentially leading to hypothyroidism.
Supplements
- As a reminder, supplements should be personalized based on symptoms, labs, medications, and medical history, but there are a few supplements that support the thyroid:
  - Selenium (especially for autoimmune thyroid support in appropriate individuals)
  - Zinc
  - Magnesium glycinate
  - Omega-3 fish oil
  - Vitamin D (if deficient)
  - Iron (only when deficiency is confirmed)
  - Myo-inositol
  - High-quality multivitamin to fill nutritional gaps

Read more about essential nutrients for thyroid production by reading my previous blog, “Nutrients for Optimal Thyroid Function.”

Test, Don’t Guess

If you're experiencing persistent fatigue, unexplained weight changes, constipation, hair loss, irregular cycles, or brain fog, don't assume it's "just getting older" or "normal." A comprehensive evaluation—including thorough thyroid testing and a root-cause approach—can help identify what's really driving your symptoms and create a personalized plan to help you feel your best.