Brown fat modulates thyroid function
Summary
Although most medical doctor's believe that Hashimoto's thyroiditis is a life-long, degenerative autoimmune disease, some people have reversed their Hashimoto's by adopting a practice of ice baths and ketogenic diet.
The mechanisms of thyroid modulation via cold water immersion therapy act through activation of brown fat (brown adipose tissue, BAT).
When activated by cold, BAT produces thyroid hormone that modulates thyroid function and regulates metabolism.
Without regular cold stimulation, brown fat disappears in the adult human body, and the thyroid can become dysregulated.
Restoration of brown fat via ice bath or cold plunge can restore proper thyroid function.
Hashimoto's reversal: Miracle, or science?
Most medical doctors will tell their Hashimoto's thyroiditis patients that they suffer from a chronic, degenerative, permanent autoimmune disorder that will require a lifetime of prescription medications that will fail to cure the underlying disease.
But not Dr. Courtney Hunt.
She was a Hashimoto's patient herself, until she reversed her condition with a ketogenic diet and cold plunging.
Dr. Hunt has discontinued her thyroid medications, and her health is better than ever.
By any medical measure, she is free of symptoms, blood markers, and medications.
Her story, and others like hers, begs for further, scientific investigation, particularly with regard to cold water immersion therapy.
Can cold exposure reverse Hashimoto's?
The connection between hypothyroidism and deliberate cold exposure has long been a topic interest in the medical community. For example, it is well understood that patients with hypo- (under active) thyroidism suffer from cold intolerance, and it makes sense. The thyroid is something like a thermostat for the body. When we are exposed to cold, the thyroid signals our brown fat cells to begin metabolizing the energy stored in our white fat, to produce heat to keep us warm.
The process is called thermogenesis.
The problem is that in highly industrialized countries like the United States and Western Europe, technologies like central heating, a trend towards urbanization and office jobs, and a preference for thermal comfort have resulted in a population that is so rarely exposed to cold that most adults have lost nearly all brown fat -- so there's nothing left for the thyroid to signal. In fact, brown fat is so rare in adult humans living in highly industrialized setting that until the 1970's medical scientists thought brown fat was just baby fat that adults eventually grew out of. In fact, regular exposure to cold in adulthood will recruit new brown fat cells, increasing our capacity for thermogenesis.
Without brown fat, most of us experience discomfort when we're cold, partly because our bodies use the only other metabolic pathway available to keep us warm.
We shiver.
As I wrote in Q: Should I Shiver?, inexperienced ice bathers are likely to experience an involuntary tremor in our muscles that is fueled by glucose and lipids from the bloodstream. The shivering releases heat within our muscles, which may help prevent hypothermia for a short time. It's the body's emergency back up response to cold exposure when brown fat thermogenesis is unavailable.
For most modern adults, and especially those with an underactive thyroid (i.e., hypothyroidism), brown fat thermogenesis is never available, so cold exposure results in the body signaling an emergency and initiating shivering. That's why the conventional medical advice for cold sensitivity due to hypothyroidism is to "keep your home warm," and "avoid unnecessary exposure to cold weather" (Wentz 2015). Although this is a prescription for avoiding discomfort, it may be exactly the wrong thing to do to cure Hashimoto's.
By doing the opposite of the traditional medical advice and intentionally plunging herself into a cold water several times a week, Dr. Hunt signaled her body to recruit new brown fat cells, re-regulated her thyroid and reversed her Hashimoto's.
Existing studies of the relationship between thyroid activity and brown fat have already established the role of thyroid hormones in activating brown fat thermogenesis. For example, the Annals of Medicine (Contreras 2014) reports that brown fat "displays a high expression of thyroid hormone receptors. In fact, thyroid hormones work synergistic with norepinephrine and are required to generate a full thermogenic response." A subsequent study (Broeders et al. 2016) showed "that higher levels of thyroid hormone are associated with a higher level of cold-activated BAT."
One of the most significant findings that followed from the discovery of brown fat in adults is that it will convert inactive thyroid hormone T4 into the more active form called T3 (Laurberg et al. 2005). In this way, brown fat is more effective for regulating thyroid hormone function than the thyroid.
As a consequence of this understanding, several pharmaceutical companies have undertaken to develop drugs that initiate brown fat thermogenesis for metabolic acceleration without cold exposure. For example, a recent scientific article published in the journal Molecular Endocrinology suggests that activating brown fat metabolism is an effective mechanism for weight loss -- but rather than recommending regular cold exposure, the article suggests that synthetic drugs (called "pharmacological interventions") might provide the metabolic benefits without the thermal discomfort (Ahima 2016).
However, my view is that there is no need to develop a drug to do what the human body is already perfectly capable of doing for itself.
Until very recently, no one was studying the feedback effects that additional brown fat might have on the thyroid. Hypothetically, the thyroid doesn't just signal brown fat -- brown fat could also be signaling back to the thyroid. That is, because the thyroid stimulates under active brown fat activity, couldn't brown fat also stimulate an under active thyroid?
Lapa et al. (2015) reported findings related to that question in the Annals of Medicine. Evaluating thyroid cancer patients after total thyroidectomy, their study determined that patients with active brown fat tissue had significantly higher levels of thyroid-stimulating hormone in their bloodstreams than a control group without active brown fat. In other words, even after total removal of the thyroid gland, those patients with active brown fat were still producing hormonal signals intended to stimulate thyroid activity.
But of the 126 patients in their study only 6 were found to have active brown fat.
The best to recruit and maintain brown fat is regular cold exposure, and it's likely that cold plunge practices were critical to Hashimoto's reversals that Dr. Hunt experienced.
What this suggests is that hypothyroidism, like obesity, type 2 diabetes, and a host of other ailments may be just a suite of maladies exclusive to western, educated, industrialized, rich, and democratic (WEIRD, Henrich et al. 2010) countries characterized by technological comfort, ultra-processed diets, and a lack of cold exposure.
UPDATED 31 OCT 2024
The recently heard from a woman who was diagnosed with Grave's disease -- an autoimmune disorder that causes overproduction of thyroid hormone. Doctors recommended removal of her thyroid, ensuring a lifetime of dependence on prescription medication.
She declined the recommendation, and elected to try a regular practice of ice baths instead.
You might expect that her already high levels of thyroid hormone might get even worse by activating her brown fat, because didn't I just say that brown fat produces more T4 active thyroid hormone than even the thyroid does?
But that's not what happened. Instead of getting worse, her symptoms of Grave's disease disappeared. That's because the brown fat will modulate thyroid function. If thyroid function is to low, as in Hashimoto's, an ice bath can bring it down. And if thyroid function is too high, as in Grave's an ice bath can help bring it down.
What we can learn from this is the brown fat is not just for thermogenesis. It performs essential functions for regulating the thyroid and secreting hormones that are critical to maintaining health.
References
Ahima RS. Unlocking therapeutic potential of brown fat. Molecular Endocrinology. 2016 Mar 1;30(3):275-7.
Broeders EP, Vijgen GH, Havekes B, Bouvy ND, Mottaghy FM, Kars M, Schaper NC, Schrauwen P, Brans B, van Marken Lichtenbelt WD. Thyroid hormone activates brown adipose tissue and increases non-shivering thermogenesis-a cohort study in a group of thyroid carcinoma patients. PloS one. 2016 Jan 19;11(1):e0145049.
Contreras C, Gonzalez F, Fernø J, Diéguez C, Rahmouni K, Nogueiras R, López M. The brain and brown fat. Annals of medicine. 2015 Feb 17;47(2):150-68.
Henrich J, Heine SJ, Norenzayan A. The weirdest people in the world?. Behavioral and brain sciences. 2010 Jun;33(2-3):61-83.
Lapa C, Maya Y, Wagner M, Arias-Loza P, Werner RA, Herrmann K, Higuchi T. Activation of brown adipose tissue in hypothyroidism. Annals of medicine. 2015 Oct 3;47(7):538-45.
Laurberg P, Andersen S, Karmisholt J. Cold adaptation and thyroid hormone metabolism. Hormone and Metabolic Research. 2005 Sep;37(09):545-9.
About the Author
Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.