How Hyperthyroidism Affects Your Body: A Simple Guide

Hyperthyroidism is an endocrine condition caused by an overactive thyroid. The thyroid gland produces too much thyroid hormone, primarily T3 and T4 which results in serious health conditions. Although hyperthyroidism is not as common as hypothyroidism, 1.5 in every 100 people around the world are living with this condition.

Symptoms of Hyperthyroidism

• Cardiac conditions – rapid or irregular heartbeat, heart palpitations, heart failure
• Unintentional weight loss – although some people do experience unintentional weight gain
• Muscle weakness
• Heat intolerance
• Declined mental health – depression, anxiety, irritability, mood swings, and nervousness
• Insomnia
• Infertility
• Increased appetite
• Frequent bowel movements and diarrhea
• Excessive sweating

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 functions¹ leading to fatigue, weight gain, poor appetite, cognitive impairment, mental illness, muscle stiffness, and reduced fertility. When the thyroid produces too much T3, bodily functions are sped up. This most commonly leads to weight loss, frequent bowel movements, anxiety, difficulty concentrating, thyroid nodules, heat intolerance, and increased appetite.

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 – 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. This boost improves the absorption of folate and vitamin B12 in the digestive system.

Tetraiodothyronine (T4)

Tetraiodothyronine, commonly referred to as thyroxine or T4, is an inactive hormone produced by the thyroid gland. Once released into the bloodstream, T4 is converted into its active form, triiodothyronine (T3), by organs with significant blood flow, such as the liver, kidneys, and heart². Approximately 90% of the thyroid hormones produced are inactive T4, with only a small portion of the active T3 hormone directly synthesized by the thyroid. This makes it crucial for the body’s organs to efficiently convert T4 into T3 through the action of two enzymes: deiodinase 1 (DIO1) and deiodinase 2 (DIO2). Without this conversion, T4 remains unusable by the body’s cells.

Calcitoni

Calcitonin, while produced by C-cells within the thyroid gland, is not classified as a “true” thyroid hormone. Its primary function lies in regulating calcium and bone metabolism. The thyroid releases calcitonin in response to elevated blood calcium levels. This hormone helps reduce blood calcium by inhibiting osteoclast activity, which slows the breakdown of bone. It also promotes calcium uptake into the bone’s extracellular matrix through osteoblast activity. Osteoclasts are responsible for breaking down old or damaged bone, allowing osteoblasts to construct new, stronger bone. This cycle of bone resorption and formation is vital for maintaining bone health and strength.

Insufficient levels of calcitonin can disrupt the normal bone remodeling process, delaying the timely rebuilding of new bone. Without adequate calcitonin, the body breaks down old bone faster than it can replace it with new bone. This imbalance leads to weakened and brittle bones, a condition known as osteoporosis.

Thyroid Hormone Regulation

Our bodies sometimes 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 release³. It uses a hormone called TSH (thyroid-stimulating hormone) to manage how much hormone the thyroid releases into the bloodstream.

Most thyroid hormones in the bloodstream are attached to proteins, which keeps them inactive. When the body needs more hormones, T3 and T4, are released from these proteins to perform their functions.

Hyperthyroidism Facts

Hyperthyroidism is not fully understood. There are several conditions that can lead to an overactive thyroid but there are people with no preexisting conditions that have unexplainable hyperthyroidism. Some conditions that can lead to hyperthyroidism include Grave’s disease, thyroiditis, and thyroid nodules⁴. An overactive thyroid gland can also be caused by excessive iodine intake as well as taking too many hypothyroidism medications. Sleep is another factor in this condition as sleeping less than 7 hours per night can result in an overactive thyroid.

Hyperthyroidism disproportionately affects women compared to men, being about 10 times more common in women. While anyone can develop an overactive thyroid, this higher prevalence in women is largely attributed to their stronger immune systems,⁵ which increase susceptibility to autoimmune disorders like Hashimoto’s thyroiditis and Graves’ disease—two primary causes of hyperthyroidism. Additionally, hormonal fluctuations during menstrual cycles, pregnancy, and menopause also play a significant role in influencing thyroid function in women.

Risk Factors of Hyperthyroidism

Several lifestyle factors may increase the risk of developing hyperthyroidism, including smoking, stress, poor sleep, nutritional deficiencies, and excessive alcohol consumption. Among these, smoking stands out as the primary lifestyle factor linked to a higher risk. While the exact mechanism behind this connection remains unclear, population-based studies consistently show that smokers tend to have lower levels of TSH (thyroid-stimulating hormone) and higher levels of T3 and T4 (thyroid hormones)^6,7.

Low TSH inhibits the body’s ability to regulate thyroid hormones, leading to elevated levels of T3 and T4, which can result in hyperthyroidism. The specific components in cigarettes that contribute to this increased risk remain unknown, as cigarettes contain many chemicals that could potentially affect the thyroid gland. However, there is promising evidence from one population study showing that former smokers who had quit for 10–12 years had TSH levels comparable to those of nonsmokers⁸. This suggests that the thyroid can repair itself over time with smoking cessation, offering a clear incentive to quit smoking.

How Hyperthyroidism Affects Your Body

The thyroid gland produces hormones that influence the entire body. When T3 and T4 rise, the basal metabolic rate—the amount of energy the body uses at rest—also increases. These hormones are essential for ensuring that all the body’s cells function efficiently and effectively. However, when T3 and T4 levels are too high, the body essentially shifts into overdrive.

People with hyperthyroidism often experience symptoms such as weight loss, cardiovascular issues, fatigue, muscle weakness, heat intolerance, and, in some cases, infertility. Fortunately, there are several medical treatments and therapies available to manage an overactive thyroid. In some cases, the thyroid may recover on its own without intervention. If you have or suspect you have hyperthyroidism, it’s important to consult a doctor to determine the best course of action together.

Supporting Research