A Silent Conversation: Oestrogen Dominance and its Enduring Influence on Thyroid Health

12 Jun

In the ever-evolving landscape of endocrine health, one that garners alot of confusion and frustration is the entangled relationship between sex hormones and the thyroid gland. Increasingly, researchers and clinicians are recognising that hormonal imbalances are seldom isolated incidents; rather, they exist as pointers in a complex web of connections. Among these, the phenomenon of oestrogen dominance is emerging not merely as an outside factor in thyroid dysfunction, but potentially as a driving force in the development and exacerbation of autoimmune thyroiditis, particularly Hashimoto’s disease. This is a new understanding and one that is gaining new interest in the functional medicine and nutritional world.

Dr Izabella Wentz, a leading figure in the integrative approach to thyroid disorders, has recently drawn attention to the underappreciated role of oestrogen in modulating thyroid function and immune reactivity. Her latest analysis synthesises emerging research and clinical observation, providing a nuanced framework for understanding why so many individuals, particularly women, experience persistent hypothyroid symptoms despite ostensibly “normal” laboratory findings or even after thyroid hormone replacement therapy.

Oestrogen Dominance -its More than just Excess:

It is essential at the outset to clarify that oestrogen dominance does not simply mean an excess of oestrogen. In many instances, serum oestrogen levels may fall within laboratory reference ranges, or even appear low. Rather, oestrogen dominance refers to a relative surplus of oestrogen in comparison to progesterone, or an impaired ability of the body to adequately detoxify and eliminate oestrogen and its metabolites. This subtle but critical distinction underscores the importance of evaluating hormonal ratios and metabolic pathways, not just static hormone concentrations in blood tests.

Contributing factors to oestrogen dominance are multifactorial. They include liver congestion, gut imbalance (dysbiosis), environmental xenoestrogens (from plastics, pesticides, and personal care products), chronic psychological stress, and genetic polymorphisms affecting methylation and oestrogen metabolism, such as variants in the COMT, MTHFR, and GST genes. In a society increasingly burdened with toxicant exposure and dysregulated stress responses, it is unsurprising that oestrogen dominance is now so prevalent. It is a worrying picture and I am seeing the fall out in many young girls in their teens and 20’s with heavy, painful periods, iron deficiency anaemia, mood swings, poor skin, tender breasts, fatigue, belly bloating and increasing rates of Endometriosis and other oestrogen driven conditions.

Thyroid Vulnerability to hormonal imbalance:

The thyroid gland, as the metabolic governor of the body, is hugely sensitive to hormonal cues and inflammatory signals. Oestrogen has been shown to increase levels of thyroid-binding globulin (TBG), a protein that binds circulating thyroid hormones and renders them temporarily inactive. As TBG rises, the proportion of free, bioavailable triiodothyronine (T3) and thyroxine (T4) decreases, leading to symptoms of hypothyroidism - even if total thyroid hormone levels remain unchanged.

Furthermore, oestrogen may interfere with conversion of T4 to T3, an enzymatic process that occurs predominantly in the liver and kidneys. This conversion is vital, as T3 is the more active form of thyroid hormone and is necessary for the regulation of metabolism, mood, cardiovascular function, and cognitive performance. In this light, a woman experiencing fatigue, weight gain, cold intolerance, or depression might not be truly “euthyroid” * at all, but functionally hypothyroid due to hormonal interference. (*Euthyroid means the state of having “normal” thyroid function).

From Dysfunction to Autoimmunity:

Perhaps the most damaging aspect of oestrogen dominance is its capacity to influence immune function, particularly in women who are genetically predisposed to autoimmunity. Oestrogen exerts complex immunomodulatory effects, some of which are pro-inflammatory. In the absence of sufficient progesterone, a hormone with well-documented anti-inflammatory and immunosuppressive properties, oestrogen may amplify the production of pro-inflammatory cytokines, shifting the immune response towards Th1 or Th17 dominance, both of which are implicated in autoimmune development.

In the case of Hashimoto’s thyroiditis, this immune reprogramming may trigger the production of anti-thyroid peroxidase (TPO) and anti-thyroglobulin antibodies, which target and gradually destroy thyroid tissue. While Hashimoto’s can develop in men, it disproportionately affects women, particularly during hormonally turbulent life stages such as puberty, pregnancy, postpartum, and perimenopause. These transitions often involve abrupt fluctuations in oestrogen and progesterone, and are frequently accompanied by environmental or psychosocial stressors - further tipping the immunological balance towards “self attack” (autoimmunity).

A vicious circle..

Much clinical research supports the association between oestrogen dominance and thyroid autoimmunity. One frequently cited study from 2015 examined women with polycystic ovary syndrome (PCOS) and found that those with elevated oestrogen levels were significantly more likely to present with elevated TSH, increased thyroid antibody titres, and higher rates of Hashimoto’s diagnosis. Although causality cannot be certain, these findings reinforce the plausibility of a mechanistic link. Moreover, hypothyroidism itself may perpetuate oestrogen dominance, creating a self-reinforcing cycle. When thyroid function is diminished, hepatic (liver) clearance slows, including the detoxification of hormones and metabolic by-products and this reduced clearance allows oestrogen to recirculate and accumulate, further contributing to endocrine imbalance and inflammatory burden.

The Hormonal Crossroads in Perimenopause and its effect on the thyroid:

Perimenopause represents a particularly vulnerable period for the suspected connection with oestrogen dominance and thyroid dysfunction. As ovarian follicular activity declines, progesterone levels typically fall first and dramatically for some. Oestrogen, by contrast, often remains elevated, or fluctuates erratically, throughout the early menopausal transition. This leads to a pronounced hormonal imbalance that is not only uncomfortable but, in susceptible individuals, potentially pathogenic.

Many women in their 40s and early 50s report a sudden onset of hypothyroid symptoms: fatigue, brain fog, weight changes, hair thinning - all often dismissed as the inevitable by-product of ageing or stress. Yet these symptoms frequently correlate with biochemical signs of oestrogen dominance and subclinical thyroid dysfunction. Left unaddressed, this can evolve into overt Hashimoto’s disease or refractory hypothyroidism.

Rebalancing the Axis:

The clinical implications of this hormonal crosstalk are significant. In the UK the typical approach to thyroid testing whereby often the thyroid function is monitored SOLELY through a TSH level and a blanket prescription of levothyroxine is given, and yet, this has proven inadequate for many especially when the underlying aetiology, or root cause, lies elsewhere. A more integrative strategy requires attention to liver function, gastrointestinal health, hormonal rhythms, and detoxification pathways as well as in depth testing of the thyroid function beyond just a TSH.

In clinic, I often use the DUTCH test, a comprehensive urine-based hormone analysis, that evaluates oestrogen metabolites and progesterone status. When coupled with full thyroid panels and autoimmune markers, this provides a richer, more actionable diagnostic landscape. These tests together can help me assess what is really going on and whether this much under diagnosed interplay is behind your underlying, and often, hugely frustrating symptoms.

From a therapeutic standpoint, dietary and lifestyle interventions are KEY. A nutrient-dense, anti-inflammatory diet, rich in cruciferous vegetables, omega-3 fatty acids, fibre, and phytonutrients, can support liver function and hormone clearance. Botanicals such as broccoli extract, milk thistle, calcium-D-glucarate, amongst others, may further assist in oestrogen detoxification. Addressing stress, optimising sleep, and restoring circadian rhythms are equally vital for adrenal-thyroid-ovarian synergy.

Potentially body identical progesterone or herbal alternatives (such as chaste tree or maca) may be used to restore hormonal balance, particularly in the luteal-deficient or perimenopausal woman. However any interventions (hormonal or herbal) should only be used under strict and appropriate supervision.

Work with me..

To sum up, the link between oestrogen dominance and thyroid issues is more than just a coincidence; it’s a complex two-way conversation between your hormones, your environment, and your overall health. As Dr Izabella Wentz and others have shown, tackling oestrogen dominance can make a real difference, not only in easing thyroid symptoms, but potentially slowing or even preventing the progression of autoimmune conditions like Hashimoto’s. I am so grateful for the insights these researchers continue to bring to light.

If any of this resonates with you—maybe you’re dealing with unexplained fatigue, stubborn weight gain, mood swings, or you've been told your thyroid tests are "normal" but you still don’t feel right, this could be the missing piece. I’d love to help you get to the bottom of what’s going on. Together we can take a detailed, personalised approach to your hormone and thyroid health and help restore balance to the entire endocrine system whatever your stage of life.