Updated: Apr 14
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, 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 (Figure 2 below, 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).
Magnesium and mitochondria
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. Nonetheless, a longer-term practice of deliberate cold exposure will require more than temporary release of stored magnesium from bones.
Given the deficiency in most Western 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 & Transdermal Absorption of Magnesium
Although we have previously written that "the best studies indicate that magnesium does not enter the body through the skin (Gröber et al. 2017)," now we're not so sure. 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, it might absorb 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).
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 Forge with good results, and noticed 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 Forge 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 we do:
Towel off after your Epsom Salt Ice Bath, but don't shower.
When you leave the salt residue on your skin, you extend the amount of time for your body to absorb the magnesium. Your pores will reopen as your skin rewarms, and you might find that slow transdermal absorption has plenty of time to take place long after your 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 your deliberate cold exposure may enhance the benefits of your practice.
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