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Magnesium is Critical for Cold Thermogenesis

Updated: Jan 23


  • Magnesium deficiency is associated with physiological & psychological disorders because mitochondria depend on magnesium to catalyze hundreds of metabolic reactions.

  • Blood tests are unreliable indicators of deficiency, because less than 1% of all bodily magnesium is stored in the blood stream. Most is stored in bones.

  • During extreme cold exposure, magnesium is released from bones to the bloodstream to help power mitochondria. The more cold you dose, the more magnesium you need.

  • Diets rich in green leafy vegetables are no longer sufficient to maintain healthy magnesium levels.

  • Transdermal absorption of magnesium in Epsom salt ice baths may help meet the magnesium demands of cold thermogenesis.

Magnesium deficiency impairs metabolism

Every metabolic function in the human body relies on magnesium, including energy production, protein synthesis (Reddy et al 2018) and Vitamin D (Dai et al. 2018). Magnesium is essential for functions in the brain, liver, kidneys, and repair of DNA. People who are deficient in magnesium are at greater risk of diabetes, cardiovascular disease, Alzheimer's, major depression disorder, and a myriad of other diseases -- perhaps because magnesium plays a critical role in the function of insulin (Jahnen-Dechent 2012).

According to Castellanos-Gutiérrez et al (2018) "several studies have reported that a lower magnesium intake is associated with an increased risk of insulin resistance," and "increased magnesium intake is associated with lower body mass index, (smaller) waist circumference and lower serum glucose."

Given that the effects of magnesium deficiency are so serious, insidious, and life-threatening, you'd think that everyone who is remotely concerned about their health and well-being would be anxious to understand their magnesium balance. Yet, there is still no reliable medical test for measuring magnesium levels in the body. About 60% of total magnesium is stored in bones, with most of the rest in muscles and other cells. Only 1% of total magnesium is in the bloodstream, meaning that tests measuring blood concentrations are poor markers of magnesium sufficiency or deficiency.

For most people, maintaining sufficient levels of magnesium requires a daily intake of at least 360 mg. Green, leafy plants are the most common source, but changes in agricultural and food industry practices have stripped magnesium from the foods that used to contain abundant quantities (Workinger et al 2018).

As a consequence of these changes in agriculture and diet, most people in Western, industrialized countries fail to get the recommended daily allowance of magnesium in their diets (Barbagallo et al 2021).

Brown fat demands micronutrients

The locus of energy production in the human body is a subcellular structure called mitochondria, where oxidation of glucose, fat, protein, and ketones is controlled (Christofferson 2020). Magnesium plays a such a critical role in the mitochondria that concentrations of magnesium are about ten times higher inside the mitochondria than elsewhere in the human cell (Gout et al. 2014).

And nowhere in the body are mitochondria more densely packed than in brown fat.

Unlike white fat, which exists solely for the storage of energy in the form of fat, the principal purpose of brown fat (also called brown adipose tissue, or BAT) is to produce enough heat to keep the body warm in cold environments. The more cold exposure the human body experiences, the more brown fat the body recruits.

It may be a surprise to learn that more brown fat is associated with leaner overall body mass (Thyagarajan & Foster 2017) to such a powerful extent that clinical trials are underway to explore the possibility that brown fat may be a treatment for obesity (e.g., Cypess & Kahn 2010). Because the best way to recruit new brown fat is a regular practice of deliberate cold exposure, it stands to reason that magnesium needs will be much greater in people who use ice baths or practice cold water swimming.

In one Russian study, exposure to -70C for only 3 minutes resulted a long-lasting 5%-10% increase in magnesium concentrations in the blood (Figure 3 above, Juravlyovaa et al. 2018). Most of that magnesium was likely released from the bones, where up to one-third of the magnesium stores are available to meet immediate metabolic needs.

But what happens to the bones after they release all that magnesium? A recent study from China suggests that they may suffer a loss of strength and density. Researchers tracked bone fractures among the elderly during cold (−2C) weather events in Wuhan, China.

Freezing temperatures increased the relative risk of bone fractures in elderly (>75 yo) Chinese women over a period of several days following cold exposure -- particularly in women who have previously experienced a fracture.

Although the researchers speculate that the cause could be related to reduced Vitamin D synthesis, reduced physical activity, reduced flexibility, or increased snow & ice fall hazard conditions, none of these explanations are satisfactory. As such, we can't rule out the possibility that episodic magnesium depletion from the bones during thermogenesis can put vulnerable populations at greater risk of fracture until that magnesium is replaced.

Because the Chinese epidemiologists have no data on magnesium levels in the population they were monitoring for bone fractures, it's not possible to say whether supplementing with magnesium would rescue bone density in the cold. There's some evidence to suggest that it could. For example, one study of 15 young women showed that increased brown fat was associated with increased bone density. Researchers divided the subjects into three groups: 1) five women diagnosed with anorexia nervosa (AN), 2) five women recovered from AN, and 3) five healthy controls. In PET scans under during cold exposure, the healthy controls exhibited the greatest activation of brown fat and the greatest bone density in all groups (Bredella et al. 2012). Moreover, studies in mice indicate that increased levels of brown fat can protect against bone loss in the cold (Du et al. 2022)

Brown fat cells are packed with thousands of magnesium-hungry mitochondria, suggesting that bodies with adequate magnesium might be protected against cold-induced bone loss by recruiting and maintaining adequate levels of brown fat (i.e., brown adipose tissue, BAT).

These results suggest that a longer-term practice of deliberate cold exposure will require more than just a temporary release of stored magnesium from bones. That is, as your body builds up brown fat and produces new mitochondria (called mitobiogenesis), it will demand more and more magnesium to keep up with your accelerating metabolism.

Given the deficiency of magnesium in typical diets, and the necessity of magnesium for recruiting new, mitochondria-packed brown fat cells, regular cold plungers might do well to take a regular magnesium supplement.

Epsom salt ice baths promote transdermal absorption

Although I have previously indicated that some scientists are skeptical that magnesium can be absorbed through the skin (e.g., Gröber et al. 2017) direct laboratory measurement demonstrates that magnesium ions transit human skin, and hair follicles contribute about a third of total magnesium flux (Chandrasekaran et al. 2016). Wherever studies ruling out magnesium absorption through the skin are based on blood concentrations only, they cannot be accepted as definitive. For example, if magnesium were absorbed through the skin during an Epsom salt (magnesium sulfate) bath, that magnesium would likely absorb into into muscle cells, or be carried to the bones, without being detected by a blood draw.

Studies based on hair and urine samples have shown better results. For example, "the measurement of magnesium levels in urine showed a rise from the control level, mean 94.81 ± 44.26 ppm/mL to 198.93 ± 97.52 ppm/mL after the first bath. Those individuals where the blood magnesium levels were not increased had correspondingly large increases in urinary magnesium showing that the magnesium ions had crossed the skin barrier and had been excreted via the kidney, presumably because the blood levels were already optimal" (Waring 2015).

Ice bath protocols for magnesium therapy

One way to improve your deliberate cold exposure practice is to add Epsom Salts to your ice bath. We've added as much as 3lb to a 6ft Morozko ice bath with good results, and noticed that the ice that forms is softer and easier to break up, and the salt helps keep the water clean.

However, the fact that we're only our ice bath for 3-5 minutes at a time means that there isn't enough time in the plunge for transdermal absorption to take place thru the closed-up pores of our cold skin.

Here's what I do:

Towel off after an Epsom salt ice bath, but don't shower.

When I leave the salt residue on my skin, I extend the amount of time for my body to absorb the magnesium. My pores reopen as my skin rewarms, and perhaps that gives transdermal absorption more time to take place long after my ice bath is complete.

Given the essential role that magnesium plays in the metabolic functions promoted by deliberate cold exposure, any additional magnesium absorption that happens during my ice bath may enhance the benefits of my practice.

UPDATE 13 Nov 2022

One customer, a practicing physician, who is enthusiastic about his cold practice and a regular reader of our journal, wrote in to encourage others to monitor their magnesium. This is what he said:

Magnesium has loads of health benefits. My patients note improvement in anxiety, insomnia, vertigo, headaches, blood pressure, restless leg, constipation and a litany of other ailments. Unfortunately, with the nutrient-depleted soil resulting from changing farming practices, roughly 70% of the U.S. in the lower 48 states are magnesium deficient. There are obviously different forms of magnesium based on what the goal is (magnesium threonate for brain, traacs or malate for high absorption body, and others). Of course, this is an oversimplification. I’m glad you continue to spread the good word!!

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.

For more information on taking charge of your own physical & mental health, visit the Self-Actual Engineering newsletter at

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2 comentarios

07 sept 2022

As usual, I have a question. After an initial 3-5 pounds of pure epson salt to the bath. How often would you add more? Or not add more? After about 3 months I haven't felt the need to change my water, it still appears nice an clean. But after that long would you add some more epson salt or not?

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Add a little more Epsom salt whenever you top off the water in your Morozko Forge. For every five gallons of water, add a little less than half a pound of Epsom salt. For example, I use an empty five gallon water cooler jug to top off the water in my Morozko. I have a 6lb bag of salt, so I pour in about 1/8th of the bag when I add water. I don't even bother to measure, because it doesn't have to be exact.

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