How Hypothyroidism Affects Your Body: A Simple Guide

Hypothyroidism is an endocrine disorder where the thyroid gland does not produce enough Triiodothyronine (T3), Tetraiodothyronine (T4), also known as thyroxine or Calcitonin. These thyroid hormones control various bodily functions including but not limited to, metabolism, heart rate, muscle strength, cell regeneration, and mood. Nearly 5 in every 100 people over the age of 12 have hypothyroidism¹. If you have been diagnosed with this condition it’s important to understand how hypothyroidism affects your body.

Symptoms of Hypothyroidism

• Fatigue
• Weight gain or difficulty losing weight
• Sensitivity to cold
• Dry skin and/or hair
• Brachycardia – slow heart rate
• Brain complications – depression, mental fog, difficulty concentrating
• Joint and muscle pain
• Heavy or irregular menstrual cycles
• Constipation
• Tingling in hands and/or feet

Triiodothyronine (T3)

Triiodothyronine or T3 is an active thyroid hormone that is responsible for a variety of bodily functions. When the thyroid does not produce enough T3 it results in slowed body functions² leading to fatigue, weight gain, poor appetite, cognitive impairment, mental illness, muscle stiffness, and reduced fertility.

T3 (triiodothyronine) activates the nervous system, leading to heightened wakefulness, alertness, and sensitivity to external stimuli. It also stimulates the peripheral nervous system, enhancing reflexes and increasing gastrointestinal tone and motility. Gastrointestinal motility is the movement of food and waste throughout the gastrointestinal tract.

The thyroid hormone T3 increases the resting breathing rate and ventilation to keep oxygen levels in the blood stable when oxidation rates rise. It also helps deliver oxygen to tissues by boosting the production of erythropoietin and hemoglobin and improving the absorption of folate and vitamin B12 in the digestive system.

Tetraiodothyronine (T4)

Tetraiodothyronine also known as thyroxine or T4 is an inactive thyroid hormone. The thyroid gland releases T4 into the bloodstream. T4 is then converted into T3 by organs with high blood flow such as the liver, kidneys, and heart. 90% of the hormones made by the thyroid are inactive T4. The thyroid makes a very small amount of the active T3 hormone, meaning it is essential that your organs have the capability to convert T4 into T3 using two enzymes called deiodinase 1 (DIO1) and deiodinase 2 (DIO2). The cells cannot use T4 until they convert it into T3.

Calcitonin

Calcitonin is not considered a “proper” thyroid hormone as it is made by C-cells in the thyroid. Calcitoni plays a role in calcium and bone metabolism. The thyroid releases Calcitonin in response to high calcium levels in the blood. Calcitonin lowers blood calcium levels by inhibiting bone absorption by osteoclasts and accelerating calcium absorption into the bone extracellular matrix by osteoblasts. Osteoclasts break down old, damaged bone to allow osteoblasts to rebuild new, stronger bones³. The breaking down and rebuilding of bones is a natural and essential process to maintain bone health and strength.

Low levels of calcitonin can inhibit the timely rebuilding of new bones. When there is not enough calcitonin the body reabsorbs old bone faster than it can build new bone causing bones to become weak and brittle (osteoporosis).

Conditions that Inhibit T4 to T3 Conversion

• Impaired liver function – Most of the T4 to T3 conversion takes place in the liver⁴. If you have liver issues or an unhealthy liver, T4 to T3 conversion can be significantly affected.
• Kidney conditions – The kidneys contain DIO1 and DIO2 enzymes that convert T4 into T3. If the kidneys are not functioning properly thyroid hormone conversion can be negatively affected.
• Stress – Stress plays a major role in how the body functions. During times of stress, cortisol levels are elevated and DIO1 is suppressed⁵ making it difficult for the body to convert T4 into T3.
• Selenium Deficiency – Both deiodinase enzymes (DIO1 and DIO2) contain selenium⁶. DIO1 and DIO2 are enzymes that regulate the amount of T3 in the bloodstream and its availability to the cells for use⁷. Low levels of selenium can affect thyroid hormone conversion.
• Gut microbiome – As research on gut bacteria continues, science has made it clear that an unhealthy gut microbiome is a major component in serious health complications. Hypothyroidism is no exception⁸. Good bacteria in the gut help convert T4 to T3. It is essential to eat foods that support a healthy gut microbiome.
• Inflammation – Pro-inflammatory cytokines trigger inflammation throughout the body, worsening diseases and chronic conditions by damaging tissues. Research suggests that certain pro-inflammatory cytokines can inhibit DIO1 and DIO2 enzyme activity⁸. This can reduce the body’s ability to convert thyroid hormones effectively.

Thyroid Hormone Regulation

Our bodies require a specific amount of thyroid hormones, sometimes they need more, sometimes they need less. The thyroid gland relies on support from the pituitary gland, located in the brain, to produce the right amount of hormones. The pituitary gland plays a crucial role in regulating various bodily functions, including controlling thyroid hormone release¹⁰. It uses a hormone called TSH (thyroid-stimulating hormone) to tell the thyroid gland how much thyroid hormone to make and when to release it.

Most thyroid hormones in the bloodstream are attached to proteins, which keeps them inactive. T3 and T4 are released from the protein when the body needs more hormones. They enter the body cells and perform their necessary functions.

Iodine and Hypothyroidism

Iodine is a trace element that plays a very important role in thyroid hormone production. Every molecule of thyroid hormone has between 1-4 atoms of iodine attached. Iodine is an essential part of thyroid hormone production. Without proper amounts of iodine, it is not possible for your thyroid to operate properly.

The stomach and duodenum absorb iodine from food. Once absorbed, it is transported to the thyroid gland, where it assists in the production of T3 and T4. Since the body cannot produce iodine on its own, it’s essential to consume iodine-rich foods like seafood, seaweed, sardines, eggs, beef liver, poultry, red meat, and pork.

Chloride, fluoride, and iodine have similar structures, which means that chloride and fluoride can potentially block iodine receptors. If you’re consuming water or using products that contain chloride or fluoride, these substances might interfere with how iodine is used by the thyroid gland, potentially disrupting its proper function.

How Hypothyroidism Affects Your Body

The thyroid gland produces hormones that affect the entire body. As the levels of T3 and T4 hormones increase, the basal metabolic rate (the amount of energy your body uses at rest) also rises. The proper thyroid hormones, T3 and T4 make all the body’s cells work efficiently and effectively.

This is why, when you have hypothyroidism (a lack of thyroid hormones), you may experience health issues due to the cells not functioning properly. An underactive thyroid can lead to weight gain, increased sensitivity to cold, bradycardia (slow heart rate), and various other signs, symptoms, and conditions.

Underactive thyroid, or hypothyroidism, is a widespread issue. While about 1 in 100 people are diagnosed with it, an estimated 12 million cases remain undiagnosed in the United States alone. If left untreated, hypothyroidism can lead to serious health problems such as heart disease, osteoporosis (brittle bones), high cholesterol, and even premature death.

If you’re showing signs of hypothyroidism, it may be a good idea to discuss thyroid testing with your doctor. Make sure to ask for a T4 test in addition to the thyroid-stimulating hormone (TSH) test. For a more detailed understanding of your thyroid function, you can also request a reverse T3 test, which measures the levels of T3 in your blood.