It is well known that those with hypothyroidism have poor tolerance to cold weather. The thyroid is heavily involved in metabolism and acts as a sort of thermostat for the body. When it becomes dysfunctional, it gets worse at regulating temperature and does not handle cold weather as well. Common advice is to avoid the cold. Is it possible that cold exposure is exactly what we should be doing? If we progressively improve the body’s tolerance to cold, can we influence the thyroid?

Homeostasis is the body’s desire to maintain balance, and we have many regulators of the body such as pH level, O2/CO2 levels, and blood-glucose. These regulators are tightly regulated; for example, if you are exercising vigorously, you are rapidly depleting oxygen because your muscle is using it. To increase oxygen levels, you’ll start breathing through your mouth. As you exercise more, the demand for oxygen decreases because you are becoming a more efficient machine so you will be able to exercise longer and harder before needing to breathe through your mouth. This is called “adaptive homeostasis” and is the basis behind any kind of performance training. This, by the way, is information from a course I just took from Dr. Mike T. Nelson called “Physiologic Flexibility” (which I highly recommend).

What is interesting is that these homeostatic regulators are two way streets, meaning if you work on your ability to be in a hypoxic state (low oxygen), it can increase your exercise tolerance and vice versa.

Temperature is also a homeostatic regulator. So if homeostatic regulators are two way streets, and those with hypothyroidism poorly tolerate the cold, can we influence the thyroid by cold water immersion? There is some preliminary research that suggests this might be true.

In 2014, a study was conducted in New Zealand (Mustafa & Elgazzar) where they took white rabbits and kept them in a cold room (39.2 degrees Fahrenheit) for 7 weeks. Compared to a control group, the cold group had more free T3 and T4 (thyroid hormones), had more conversion of T4 to T3, and increased uptake of the thyroid; all indicators of improved thyroid function. 

Of course these are rabbits, and their physiology is not identical to ours. It’s hard to get human volunteers to sit in a cold room for 7 weeks, nor would any ethics board approve it. However, with the popularity of cold water immersion on the rise, this could be an easily conducted study in humans. 

How can we explain this? Two words, Brown Fat. Well actually it’s 3, Brown Adipose Tissue, which I’ll abbreviate to BAT. There is white fat, or WAT, and BAT. The difference is that BAT has mitochondria in it which are metabolically active and are what make the change from a white color to brown color. Babies are born with a lot of BAT and it’s why babies don't shiver. The mitochondria are able to regulate temperature. Our body has a few ways to warm up, through mitochondria and through shivering. The fact that babies have BAT is the reason they don’t shiver. It was long thought that as we age, we convert BAT to WAT and then the need to shiver increases. However, it may be due to a modern lifestyle and less exposure to the elements. 

There are tons of studies that show that cold exposure can convert WAT to BAT such as this one. And this study shows that higher levels of BAT are associated with higher levels of thyroid hormone. 

I think it is fascinating that something as simple as cold exposure may have an influence on our endocrine system, and this could have huge implications. Hopefully, there will be more evidence coming out on this topic, meanwhile, I’ll be jumping in my ice bath. 

References:

Broeders EPM, Vijgen GHEJ, Havekes B, Bouvy ND, Mottaghy FM, et al. (2018) Correction: Thyroid Hormone Activates Brown Adipose Tissue and Increases Non-Shivering Thermogenesis—A Cohort Study in a Group of Thyroid Carcinoma Patients. PLOS ONE 13(12): e0209225. https://doi.org/10.1371/journal.pone.0209225

Mustafa S, Elgazzar A. Influence of chronic exposure to cold environment on thyroid gland function in rabbits. Horm Metab Res. 2014 Jul;46(8):546-9. doi: 10.1055/s-0033-1363284. Epub 2014 Jan 20. PMID: 24446160.

Peres Valgas da Silva C, Hernández-Saavedra D, White JD, Stanford KI. Cold and Exercise: Therapeutic Tools to Activate Brown Adipose Tissue and Combat Obesity. Biology (Basel). 2019 Feb 12;8(1):9. doi: 10.3390/biology8010009. PMID: 30759802; PMCID: PMC6466122.