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A recent study estimated the prevalence of hypothyroidism (low levels of thyroid hormone) in the gender-diverse population to be almost 9%. This level is higher than in the general population. This surprising statistic begs the question: can gender-affirming hormonal therapy like estrogen or testosterone trigger hypothyroidism or the autoimmune thyroid disease known as Hashimoto’s thyroiditis?
To address that question, we need to start where all the action begins: in the brain!
The hypothalamus-pituitary axis is a feedback control system. It connects our central nervous system with our endocrine system. Your hypothalamus, located in your brain, receives information about hormone levels in your body. In response, it signals your pituitary gland, also in your brain, to increase or decrease the release of stimulating hormones.
Stimulating hormones cause their target gland to release more hormones. Types of stimulating hormones include:
- Thyroid-stimulating hormone (TSH): tells your thyroid gland to release thyroid hormone
- Adrenocorticotropin hormone (ACH): signals your adrenal gland to release steroid hormones (cortisol and androgens)
- Luteinizing hormone (LH) and follicle-stimulating hormone (FSH): increase production of the sex hormones estrogen and testosterone in the ovaries and testes
Most of the time, your hypothalamus-pituitary axis can adjust hormone production to keep hormones balanced and ensure normal thyroid function. But this balance is affected by:
- Certain medications, including estrogen and testosterone therapy
- Autoimmune thyroid diseases like Hashimoto’s thyroiditis or Graves’ disease
- Nutritional deficiencies
Why is this important? Gender-affirming hormonal therapy requires prescription treatment with sex hormones for transitioning. These hormones include:
- Feminizing hormonal treatment: estrogen or estrogen with testosterone-lowering (anti-androgen) medications
- Masculinizing hormonal treatment: testosterone and sometimes progesterone
Sex hormones influence normal thyroid function through their effect on binding globulins. Binding globulins are proteins that bind to specific hormones. Since your body can’t use bound hormones, hormone production usually increases.
Thyroxine binding globulin
Thyroxine binding globulin (TBG) attaches to thyroid hormone.
High levels of estrogen trigger the release of more TBG. As more thyroid hormone binds to TBG, thyroid hormone levels drop. This triggers the release of TSH. In response, your thyroid gland releases more thyroid hormone.
Taking estrogen or testosterone can affect TBG concentrations, even if in opposite ways. To account for these changes, a normal thyroid gland in non-transgender women and non-transgender men adjusts the production of thyroid hormone and TSH. But those receiving gender-affirming therapy may:
- Need an increase in the previously-prescribed dose of thyroid medication
- Discover an undiagnosed thyroid disorder or autoimmune disease
Sex hormone-binding globulin
Sex hormone-binding globulin (SHBG) binds to testosterone and the estradiol form of estrogen. Once bound, these hormones become inactive. In response, the body makes more sex hormones to make sure your body has enough available. But what is the link to thyroid hormone?
Thyroid hormone plays a role in how much SHBG your liver makes. As thyroid hormone production increases, your liver produces more SHBG. In fact, taking thyroid hormone replacement medication increases your SHBG levels.
During gender-affirming therapy, your SHBG levels change based on the treatment. Estrogen therapy causes an increase in SHBG, while testosterone causes a decrease. These changes in SHBG levels may have an effect on your thyroid hormone levels.
Hashimoto’s thyroiditis is an autoimmune disorder and the primary cause of hypothyroidism. In autoimmune diseases, your immune system mistakenly attacks healthy tissues. This causes chronic inflammation and/or immune reaction. An immune reaction is how your body identifies and defends itself against foreign invaders.
Inflammation and/or an immune reaction can increase the amount of estrogen the body makes. Thus, excess estrogen, as frequently seen in transgender women, may increase one's risk of developing an autoimmune thyroid disease like Hashimoto’s thyroiditis.
That was a lot of information. Let’s summarize what we covered:
- Hypothyroidism is more common among the gender-diverse population compared to the general population.
- Our hypothalamus-pituitary axis controls our hormone balance. Medications, autoimmune disorders, or stress can alter this balance.
- High estrogen levels increase the risk of developing Hashimoto’s thyroiditis.
- Thyroid hormone levels influence the amount of sex hormones produced by our body.
- Estrogen is the main hormonal treatment in transgender women. It lowers thyroid levels -- and can increase the risk of developing hypothyroidism -- by increasing TBG levels.
- Testosterone, the main hormone therapy for transgender men, decreases TBG levels.
Even small changes in our hormones can cause big changes in our bodies. It is suggested that after starting or stopping gender-affirming therapy get thyroid levels checked around 6 to 8 weeks later. Those undergoing gender-affirming hormone treatment should also have regular thyroid testing to evaluate whether the hormonal treatment is affecting thyroid function.
Frequent monitoring of thyroid levels can be convenient and easy with Paloma's home Thyroid Test Kit. this test accurately measures your Thyroid Stimulating Hormone (TSH), Free Thyroxine (Free T4), Free Triiodothyronine (Free T3). Thyroid Peroxidase Antibodies (TPOAb) are also included in the panel, to help identify autoimmune thyroid disease. Getting an accurate diagnosis and effective hypothyroidism treatment is also made easy with Paloma's team of thyroid doctors. Our thyroid-savvy healthcare providers can guide you toward successful treatment options, and put you on the path to healthy living.