The thyroid gland and the brain have a close-knit relationship. This two-way street of communication helps to maintain hormonal harmony in the body. When circulating levels of thyroid hormone are low, the brain (via the hypothalamus and pituitary gland) secrete TRH and then TSH to stimulate the thyroid to produce more hormones until proper amounts are reached in circulation. This is why TSH levels are inversely associated with thyroid status— meaning the higher the number, the more hypothyroid.
As with any relationship, this open communication is imperative to maintain the status as “in a relationship” instead of “it’s complicated”. When either party begins to disrupt communication, the relationship will struggle.
Common reasons for brain-thyroid communication interruptions:
Autoimmunity: One of the most common reasons(upwards of 95% of the time) for this includes thyroid damage related to Hashimoto’s (autoimmunity) in which the inflammatory damage is too great for the thyrocytes (cells in the thyroid) to properly produce adequate amounts of thyroid hormone. No matter how hard the brain works to produce TSH and stimulate the thyroid, the thyroid just can’t perform the task.
HPA Axis dysfunction: the HPA-Axis stands for the hypothalamus, pituitary, and adrenal axis. This brain-adrenal axis communicates directly to the thyroid gland. Stress impacts this pathway greatly and can disrupt communication, leading to hypothyroidism. Cortisol, the stress hormone, will block the hypothalamus from producing TRH, which then affects the pituitary gland’s secretion of TSH, and thus the thyroid releases less thyroid hormone. To top it off, stress will impair the T4 to T3 conversion and lead to perpetuating hypothyroid symptoms! (Psst.. this is one reason that relying on TSH alone isn’t an accurate picture of what’s truly going on!).
Nutrient deficiencies: the production of thyroid hormones, communication from the brain to the thyroid, conversion of inactive to active thyroid hormones, and the utilization of thyroid hormones into the cells is highly nutrient dependent. Micronutrients like sodium, potassium, magnesium, calcium, iodine, selenium, zinc, inositol, glutathione, and several other nutrients are needed for this to function optimally. Demand for nutrients increases during times of stress, inflammation, healing, injury, exercise, and growth.
Inflammation: inflammation impairs many functions, including the efficiency at which thyroid hormone is able to get into the cells, how well the body converts thyroid hormones from inactive to active, as well as the speed of synapse inside the brain. (More on this later!)
Thyroid hormones have a direct impact on mood. As the regulator of your metabolic pace, thyroid hormones help you to have energy, stamina, and motivation. Low levels of thyroid hormone can lead to fatigue, lethargy, and even anxiety and depression. The most common neurological complaints of those with Hashimoto’s and/or hypothyroidism include depression, fatigue, and brain fog.
So what’s going on, exactly?
Thyroid hormones have immuno-modulating properties. Low thyroid hormones in the brain suppress the anti-inflammatory immune response which can prolong inflammation. The brain contains high amounts of cells called microglials. These are responsible for preventing harmful foreign invaders from entering the brain and causing harm. They are also responsible for cleaning up debris, including plaques, that form in the brain. Most of the human body has “attack” cells and “stop attack” cells (sort of like a checks and balances), but the brain has a disproportionately higher number of “attack” versus “stop attack”. This makes turning off an inflammatory immune response harder in the brain versus elsewhere. Thyroid hormones are one of the few modulators (regulators) of inflammatory immune reactions in the brain, therefore making a hypothyroid state a factor in perpetuating levels of inflammation and hyperactive immune responses.
The intimate relationship between thyroid hormones and neurotransmitters. Serotonin is a chemical that carries messages between nerve cells in the brain and throughout your body. Serotonin plays a key role in such body functions as mood, sleep, digestion, nausea, wound healing, bone health, blood clotting and sexual desire. Serotonin helps the pituitary gland secrete TSH, which then triggers the thyroid to produce more thyroid hormone. When thyroid hormone levels are low, there is an increase in the turnover and excretion of serotonin. This creates a vicious cycle where low thyroid leads to low serotonin which then suppresses TSH and thus low thyroid hormones… repeat! Low serotonin levels are linked to depression, cravings, sleep disturbances, and digestive issues. Dopamine, another “feel good, reward” neurotransmitter, also helps to release TSH from the pituitary gland. When levels are low, the thyroid may release less thyroid hormone due to lack of stimulation from TSH. Like serotonin, low thyroid status can lead to low dopamine, which can lead to symptoms of poor energy, poor memory, impulsivity, and poor information retention.
Inflammation from the autoimmune process increases inflammatory levels in the brain. Brain inflammation is one of the leading causes of brain fog and slowed synapses that is linked to depressive symptoms. In fact, studies show that people with autoimmune disease, which is an inflammatory disease state, have higher rates of inflammation related mood disorders.
Thyroid dysfunction has also been linked to a higher likelihood of developing obsessive compulsive disorder. In fact, one study showed that nearly 40% of those with OCD have autoimmunity, with Hashimoto’s being one of the most commonly reported.
Those with thyroid dysfunction, specifically Hashimoto’s, are often times more likely to relate to being “Type A” personality. It is uncertain which is the primary driver— the Type A personality being associated with less stress reliance and thus creating an environment favorable for autoimmunity and/or hypothyroidism OR if hypothyroidism is impacting neurotransmitters and leading to mood changes and obsessive-compulsive behaviors. I won’t pretend to be an expert in mental health, but I do think it’s valuable to be reminded of just how connected everything is in our bodies!
So what can you do to help manage nutritionally:
Try not to skip meals. The body works best in a fed state. Going too long without eating during the daytime hours when your body and mind are busy at work is a big stressor for the system. A good rule of thumb is to have a meal at least every 4-5 hours. If you need a snack, then have a snack about 2-3 hours between meals. The size of the snack will be larger the further away the meal times are. This creates an environment of “blood sugar stability” which is the foundation of all nutritional therapies!
Eat enough food. Our bodies are wildly effective at adaptation. Adaptation to chronic under-eating often results in slowing down of the metabolic pace— which is primarily set by the thyroid! Food provides calories. Calories are a form of energy. Therefore, low calorie intake is associated with lower energy production and lower metabolic rate. Think of weight management more about increasing metabolic rate as opposed to just decreasing calories. Not sure if you’re eating enough or too much? This is where a professional (like me!) Can help identify trouble spots in your typical food habits that may be tripping you up!
Be sure to enjoy your food too! While sometimes there do have to be some limitations and boundaries with foods to allow the body to function optimally, within those boundaries it is important to find joy, abundance, and satisfaction. Again, a professional can help you shift the mindset from deprivation to nourishment and help with making food fun again!
Manage inflammation by limiting ultra-processed foods and emphasizing naturally vibrant colors on your plate. If you get 2 or more brightly colored foods at meals, you’re headed in the right direction!
Consider brain-specific nutrients including magnesium, potassium, inositol, serine, Vitamin C, B-Vitamins which all support the HPA-Axis. I always opt for intra-cellular micronutrient testing to determine levels of nutrients and provide individualized recommendations for repletion. (NOTE: please don’t take these supplements without discussing with your provider! Everyone is different!). Test, don’t guess!
Oh, and if you’re a fellow Type- A like me, it’s extra important that you manage stress. Try these:
Some brain-specific superfoods include:
Disclaimer: Please note that “Thyroid School” emails from Chews Food Wisely, LLC (and Nicole Fennell, RD) are not intended to create any physician-patient relationship or supplant any in-person medical consultation or examination. Always seek the advice of a trained health professional with any questions you may have regarding a medical condition and before seeking any treatment. Proper medical attention should always be sought for specific ailments. Never disregard professional medical advice or delay in seeking medical treatment due to information obtained in “Thyroid School” emails. Any information received from these emails is not intended to diagnose, treat, or cure. These emails, websites, and social media accounts are for information purposes only. The information in these emails, websites, and social media accounts are not intended to replace proper medical care.
Nicole Fennell is a functional nutrition Dietitian—and a fellow Hashimoto’s patient—who understands firsthand the challenges of living with thyroid hormone imbalances and immune system dysfunction. Her approach to managing chronic disease and stubborn symptoms focuses on building the body up with enjoyable and realistic nourishment rather than breaking it down with restrictive, unrealistic, short-term diets.
With a real-food philosophy, Nicole emphasizes the power of nutrition, movement, and peace of mind in both disease prevention and long-term health. Outside of her work, she loves staying active with her husband and three kids, lifting weights, practicing yoga, walking, cooking, enjoying good food, and spending time outdoors.
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