The Hashimoto's and Brain Connection Nobody Talks About

By Anca Vereen, Integrative Dietitian

Of all the things I discuss with my Hashimoto's clients, this is the one that consistently brings people to tears: being told for years that their cognitive and mood symptoms are anxiety, depression, stress, or simply part of getting older. And then discovering that their thyroid antibodies have been attacking their nervous system the entire time.



I want to be very clear about something. Brain fog with Hashimoto's is not a vague, poorly understood side effect of low thyroid hormones. It has very real, identifiable physiological mechanisms. And for many people, treating those mechanisms rather than simply adjusting thyroid medication is the missing piece.

How Hashimoto's Affects the Brain

Research consistently shows that thyroid hormones play a fundamental role in brain function. They regulate neurotransmitter production, synaptic activity, and the health of the myelin sheath that insulates nerve fibres. When thyroid hormone activity is impaired, as it is throughout the fluctuating course of Hashimoto's, the downstream effects on the brain are significant.

But here is where it gets more complex. The autoimmune process in Hashimoto's does not always stay neatly confined to the thyroid gland. The same antibodies that attack thyroid tissue can cross-react with structures in the brain and nervous system.

TPO antibodies, the most commonly measured Hashimoto's antibody, have been shown to cross-react with the cerebellum. GAD-65 antibodies, which can be elevated in Hashimoto's, drive cerebellum autoimmunity directly. Myelin basic protein antibodies can trigger demyelination. Transglutaminase-6 antibodies, particularly relevant in those with gluten sensitivity, are also associated with cerebellar autoimmunity.

Research has confirmed that patients with Hashimoto's, even those who are euthyroid (meaning their thyroid hormone levels are technically normal), can have subtle but measurable brain dysfunction. The conclusion from studies in this space is worth sitting with: neurocognitive functioning and psychological wellbeing may not be fully restored by thyroid hormone replacement alone.

The Symptoms That Tell You the Brain Is Involved

Cerebellar involvement in Hashimoto's is more common than most people realise, affecting an estimated 10 to 20 percent of patients to some degree. The symptoms are often dismissed or misattributed.

They include poor balance and instability, vertigo, anxiety that worsens in crowded spaces, nausea with movement, car sickness, and sensitivity to sound and light. On clinical examination, findings may include a positive Romberg's test, ataxia (coordination difficulties), difficulty with rapidly alternating movements, and a wide-stance gait.

Beyond the cerebellum, Hashimoto's drives neuroinflammation through cytokine activation of microglia, the brain's resident immune cells. When microglia become chronically primed, they amplify inflammation in the brain even in the absence of an ongoing external trigger. This is the mechanism behind the persistent brain fog, fatigue, and mood dysregulation that so many Hashimoto's patients describe. The brain is inflamed and it cannot work properly.

Blood-brain barrier permeability, what some call a "leaky brain," is also a consequence of ongoing systemic inflammation. When the barrier that normally protects the brain becomes compromised, inflammatory mediators, antibodies, and toxins gain access to neural tissue, amplifying the neuroinflammation further.

The Depression and Anxiety That Is Not Just Depression and Anxiety

Research has found that elevated thyroid antibodies are independently associated with more severe depressive episodes, particularly in older patients. The conclusion from these studies is that increased anti-thyroid antibody levels may indicate an unknown autoimmune process affecting the central nervous system, or that the antibodies themselves are directly pathogenic.

This is not semantics. It matters clinically, because depression driven by neuroinflammation and autoimmune reactivity does not respond to antidepressants the same way that non-inflammatory depression does. If we are not addressing the immune driver, we are not addressing the depression.

The same applies to anxiety. In my practice I see a very consistent pattern: women with Hashimoto's who have been on antidepressants or anti-anxiety medications for years, with limited relief, whose symptoms dramatically improve when we address the autoimmune and inflammatory drivers of the condition.

What This Means Practically

Supporting brain health in Hashimoto's requires working on multiple levels at once.

Reducing the overall inflammatory load on the immune system is the foundation. This means dietary changes, gut health support, blood sugar regulation, and stress reduction, all of which I cover in other posts in this series.

Supporting antioxidant status is particularly important for the brain. Thyroid hormones have a protective role in modulating antioxidant levels, and tissue hypothyroidism worsens oxidative stress. Key antioxidants for Hashimoto's and brain health include glutathione, vitamin C, vitamin E, and alpha lipoic acid.

For those with cerebellar symptoms or balance issues, addressing the specific antibodies driving cross-reactivity is essential. This includes gluten elimination (TPO antibodies cross-react with cerebellar tissue, and gluten is a major driver of transglutaminase-6 antibodies), as well as deeper immune modulation strategies.

Supporting neurotransmitter balance through nutritional means, including adequate protein, iron, B vitamins, and magnesium, can meaningfully support mood and cognition alongside the broader autoimmune work.

And acknowledging these symptoms as real, physiological, and worthy of attention, not as anxiety or hypochondria, is often where real healing begins.

Anca Vereen is an integrative dietitian specialising in autoimmune and hormonal health. Visit ancavereen.com for personalised support.