Medically reviewed by
Dr. Minako Abe, M.D., Board-certified emergency medicine physician researching the relationship between lifestyle and disease onset in relation to the immune system and cancer, Japan
Ever wondered why you sneeze when pepper tickles your nose? The truth is sneezing isn’t just an everyday nuisance. This reflex is actually a physiological response. Think of it as your body’s way of kicking out irritants and pathogens (germs) from your nasal passages to prevent a potential infection.
The function of the immune system goes far beyond just hypersensitivity reactions (which include what we typically think of as allergies). One of the things that makes the immune system so fascinating is how it works constantly to keep us healthy in many ways that we are not consciously aware of.
But, what does your body’s “defense system” have to do with your thyroid? Is there even any connection between the two?
In this article, we will look at the following:
What is the thyroid?
The thyroid gland is a butterfly-shaped organ at the base of your neck. Thyroxine (T4) and triiodothyronine (T3) are the two main thyroid hormones produced by this gland. These hormones regulate metabolism, heart rate, body temperature, and other vital bodily functions.
The production of T4 and T3 is controlled by the hypothalamus and pituitary gland through a feedback mechanism involving thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH). When thyroid hormone levels are low, the hypothalamus releases TRH, which stimulates the pituitary gland to produce TSH. TSH then signals the thyroid gland to release more thyroid hormones. When thyroid levels of thyroid hormone levels are high, they signal the hypothalamus and the pituitary gland to reduce their production of TRH and TSH, respectively. This reduction in TRH and TSH decreases the stimulation of the thyroid gland.
Abnormal thyroid hormone levels are commonly classified by thyroid activity: hyperthyroidism, where the thyroid is overactive, and hypothyroidism, where the thyroid is underactive.
What is the immune system?
The immune system is a complex network of cells (your white blood cells), tissues, and organs that work together to defend the body against harmful pathogens, such as bacteria, viruses, and parasites. It has two main pathways: the innate and adaptive immune systems.
The innate immune system acts as the body’s first line of defense against any invading pathogens and is active from the moment of exposure. It includes physical barriers like the skin and mucous membranes, as well as immune cells such as neutrophils, macrophages, and natural killer cells. The innate immune response is not specific to a particular type of pathogen; it aims to stop all pathogens similarly. This response is also immediate, with reactions occurring within minutes to hours after exposure to a pathogen.
The adaptive immune system, on the other hand, is highly specific to the pathogens it has encountered before. The adaptive immune response is slower to activate, taking days to develop, but it is more precise in its action against pathogens. This system also has the ability to remember specific pathogens, which makes future responses to the same pathogen faster and more efficient. This adaptive immune system includes T cells, which can directly kill infected host cells or help other immune cells, and B cells, which produce antibodies that target and neutralize pathogens.
Our immune system also has this remarkable ability called immunosurveillance. As the name implies, certain immune cells are constantly on the lookout for and getting rid of foreign invaders like bacteria and viruses, as well as precancerous and cancerous cells within the body.
How do the thyroid and immune system influence each other?
Research has shown that the relationship between your thyroid and immune system is bidirectional. This means that:
1. Thyroid hormones influence the immune system
Thyroid hormones play a role in regulating immune function by influencing the production and activity of your immune cells. These immune cells produce proteins known as cytokines. Cytokines are like the “messengers” of the immune system. They serve as signals that tell other immune cells where to go and what to do, such as speeding up the maturation of more immune cells, calling for reinforcements to a site of infection, or helping heal damaged tissue.
As far as the effects of thyroid disorders like hypothyroidism and hyperthyroidism on the immune system go, it’s a complex matter. Although this topic has been extensively researched, according to a review article in the Frontiers in Endocrinology journal, the data can be challenging to interpret or appear inconsistent.
For instance, hypothyroidism has been associated with a weakened immune response and an increased susceptibility to infections, but this doesn’t mean that it’s always true for every single case of hypothyroidism. Research shows that the exact impact can vary depending on factors like the individual specific immunological phenotype and severity of the thyroid disorder (in this case, hypothyroidism). According to an article published in the Southern Medical Journal which describes the case of a severely hypothyroid 71-year-old man, uncontrolled hypothyroidism might impair immune function, but proper treatment with levothyroxine can restore normal immune function.
On the other hand, research suggests that hyperthyroidism may be associated with an increased activity of some parts of the immune system. People with hyperthyroidism might have a more active B cell response (also known as humoral immune response), leading to the production of more antibodies. While this may sound like a good thing, it really isn’t. This is because a hyper-responsive immune system may lead to hypersensitivity (an exaggerated immune response to a particular substance, often causing allergies) and autoimmune reaction (a condition where the immune system mistakenly attacks healthy tissues in the body).
2. The immune system can also affect the thyroid
Immune system activity can trigger inflammation, which triggers the release of cytokines. High levels of certain cytokines can impair thyroid hormone production and activity. Not only does inflammation interfere with the conversion of T4 to the more active T3 hormone, but it can also lead to autoimmune thyroid diseases like Hashimoto’s thyroiditis and Graves’ disease.
In Hashimoto’s thyroiditis, the immune system produces anti-thyroid peroxidase antibodies (TPOAb) and anti-thyroglobulin antibodies (TgAb) that target the thyroid, leading to chronic inflammation and eventual destruction of thyroid tissue. Symptoms of Hashimoto’s thyroiditis include fatigue, weight gain, depression, and cold intolerance.
In Graves’ disease, the thyroid is stimulated by the immune system. In this condition, antibodies known as thyroid-stimulating immunoglobulins (TSIs) bind to thyroid receptors, leading to excessive hormone production. This disease presents symptoms such as weight loss, rapid heartbeat, and heat intolerance.
That said, it’s worth noting there are a number of contributing factors to the development of autoimmune thyroid disorders. Some of these include genetic predisposition, environmental factors, stress, and gut health. Did you know that about 70-80% of your immune cells are in your gut? It then comes as no surprise that dysbiosis (a term referring to the imbalances in gut bacteria) has been linked to autoimmune conditions, including those affecting the thyroid.
What are some strategies to maintain thyroid health and support immune function?
1. Balanced Diet
Although it doesn’t directly “boost” the immune system, a balanced diet can support both immune function and thyroid health. Vitamin C, vitamin D, zinc, and iron are all essential for immunological activity. Protein is needed to build and repair immune cells. Omega-3 fatty acids can help reduce inflammation, which can be beneficial for a healthy immune response. Make sure to also include enough fiber in your diet as it can help promote a healthy gut microbiome, which plays a role in regulating the immune system. For your thyroid, iodine and selenium are among some of the essential nutrients you should absolutely have in your diet. Including iodized salt and seafood in your diet can help ensure you get enough iodine. Brazil nuts, seafood, and whole grains are good sources of selenium.
2. Stress Management
In response to chronic stress, cortisol (the primary stress hormone) is prolongedly released into the bloodstream. Elevated levels of cortisol can lead to the disruption of the hypothalamic-pituitary-thyroid (HPT) axis, the hypothalamic-pituitary-adrenal (HPA) axis, and the conversion of inactive T4 to active T3. The HPT axis regulates thyroid hormone production and release. The HPA axis—among its many other functions— modulates immune responses. Practicing stress-reduction techniques such as meditation, deep breathing exercises, and regular physical activity can help keep cortisol levels in check and reduce the negative effects of stress on the thyroid and immune system.
3. Regular Exercise
Beyond being a well-known stress reliever, regular exercise promotes circulation and can help reduce chronic low-grade inflammation (which weakens the immune system over time). Physical activity also triggers the release of endorphins, which have anti-inflammatory effects and can improve overall well-being. What’s more, regular exercise also helps with weight management, which is important for thyroid health. For individuals with Hashimoto’s thyroiditis and insulin resistance, regular physical activity has been shown to improve insulin sensitivity. For most days of the week, aim for at least 30 minutes of moderate-intensity exercise, such as brisk walking, cycling, or swimming.
4. Adequate Sleep
Sleep has so many benefits for the human body, but when it comes to the immune system, one key advantage of adequate sleep is that it promotes the production of cytokines. In fact, sleep deprivation has been associated with a decreased production of protective cytokines. Sleep also influences the HPT axis, specifically by influencing the production and release of hormones such as TSH and thyroid hormones. The exact amount of sleep needed can vary depending on individual factors, but most adults require around 7-8 hours of quality sleep per night.
5. Limited Exposure to Environmental Toxins
Environmental toxins, such as pollutants, heavy metals, and endocrine-disrupting chemicals, can interfere with thyroid function and immune regulation. Realistically speaking, it’s not always possible to completely eliminate exposure to environmental toxins, but there are some practical steps you can take that can go a long way in significantly reducing your overall intake or exposure. For starters, as much as possible, choose organic produce. This can help reduce your intake of pesticides and herbicides, for instance. You should also avoid plastic wrap and containers whenever possible. Opt for glass or stainless steel containers for food storage. Also, if you usually handle thermal paper receipts with bisphenol A (BPA), consider using digital receipts or washing hands after handling receipts.
6. Medical Treatment
If you experience symptoms of thyroid dysfunction or immune-related conditions, such as fatigue, weight changes, or recurrent infections, it is important to consult your healthcare provider for proper evaluation and management. While immunosuppressive drugs may be prescribed to manage some autoimmune diseases (such as lupus or Crohn’s disease), they are generally not the first line of treatment for autoimmune thyroid diseases like Hashimoto’s thyroiditis or Graves’ disease. Instead, treatments usually focus on managing thyroid hormone levels. Treatment for thyroid disorders typically involves hormone replacement therapy for hypothyroidism, or anti-thyroid medications, radioactive iodine therapy, or surgery for hyperthyroidism.
7. Nutrient Supplementation
Nutrients such as vitamin C, vitamin D, selenium, and zinc are commonly studied for their potential immunostimulating effects, but their benefits are most evident in people with deficiencies or during times of stress or illness. In cases of nutrient deficiencies, it’s best to take the specific supplements you need under the guidance of your healthcare provider. If you’ve been diagnosed with a thyroid condition such as hypothyroidism or hyperthyroidism, always remember that supplements are not a replacement for your medications.
Key takeaways
- The relationship between thyroid health and the immune system is complex and bidirectional.
- Thyroid hormones influence the activity and development of immune cells, as well as their ability to fight off infections.
- Thyroid dysfunction can either overstimulate the immune system, increasing the risk of autoimmune diseases, or weaken it, making the body more susceptible to infections.
- Autoimmune disorders, inflammation, and stress can all influence thyroid function and immune function.
- While thyroid issues can affect the immune system, it doesn’t necessarily mean everyone with a thyroid condition will have a weakened immune system.
- Adopting a healthy lifestyle can support both thyroid health and immune function. This includes regular exercise, stress management techniques (such as meditation or yoga), adequate sleep, and a diet rich in essential nutrients.
- If you have any concerns about your thyroid health or immune function, consult your doctor. They can assess your individual situation and recommend the best course of action.
