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Ice Baths, Hypertension & Hormesis

Updated: Jan 23

Brown fat may be critical to managing blood pressure

Hypertension in the elderly

I got a question from an older customer who stands out in his social circle because some of his friends can't believe he's crazy enough to practice regular ice baths. Nevertheless, he's been consistent in his pursuit of deliberate cold exposure, and so you can probably imagine his friends ask him a lot of questions about it.

Today, he passed this one on to me:

What’s the effect on high blood pressure from the ice bath?

For many older Americans, hypertension (chronically elevated high blood pressure) is a serious concern. The CDC estimates that over 60% of the US population over 60 years old are either take medication for high blood pressure, or experience systolic blood pressure greater than or equal to 140 mmHg, or diastolic blood pressure greater than or equal to 90 mmHg.

Because elevated high blood pressure can be associated with shorter life expectancy, it may be that our customer's friends are asking about the effects of the ice bath out of a legitimate concern for his medical safety.

A number of scientific studies reinforce their concerns. For example, Hintsala et al. (2013) from the University of Oulu in Finland measured the blood pressure response in 41 hypertensive men aged 55-65 years during 15 minutes of whole-body cold air exposure (−10°C, wind 3 m/s, winter clothes), compared to 20 men without hypertension.

They discovered that short-term deliberate cold exposure will elevate systolic blood pressure by 20 mm Hg or more. The Finnish researchers concluded "Short-term cold exposure increases central aortic blood pressure and cardiac workload, and myocardial oxygen demand slightly increases in relation to blood supply in untreated hypertensive middle-aged men. Because of the higher baseline blood pressure among hypertensive subjects, the cold-induced rise in central aortic blood pressure may increase the risk of adverse cardiovascular health effects."

Moreover, other studies have found similar results, even at more mild temperatures (e.g., +10°C, Korhonen 2006). As I explained in 'Are you getting enough vasoconstriction?' cold exposure causes contraction of the smooth muscle tissues that control blood flow to the extremities, thereby conserving body heat for the internal organs. The reduced blood flow to the limbs results in an increased pressure in the torso. So it makes sense that short-term cold exposure results in short-term increases in blood pressure, and the risk to those with hypertension suggests that they consult with a medical professional who knows them well prior to undertaking a practice of ice baths.

Benefits of brown fat

Over the longer-term, the metabolic benefits of the ice bath may outweigh the shorter-term risks of increased blood pressure. For example, Becher et al. (2020) compared over 5000 matched pairs of patients belonging to one of two groups -- those with brown fat, and those without. They discovered that the brown fat positive group enjoyed several health advantages over those without, including:

  • lower prevalence of type II diabetes,

  • a healthier balance of cholesterol levels,

  • lower incidence of coronary artery disease & congestive heart failure, and

  • reduced likelihood of hypertension.

They wrote:

Our study illustrates that individuals with thermogenic fat have significantly improved metabolic profiles. This effect is not only limited to diabetes, but extends to coronary artery disease, congestive heart failure and hypertension. Furthermore, the effects of brown fat on metabolic and cardiovascular disease are most pronounced among individuals with elevated body mass index. Those obese individuals who retain brown fat activity appear to be protected against conditions linked to excess weight. This notion further supports the potential of brown fat as a therapeutic target beyond weight loss itself, but as a means to uncouple obesity from disease. - Becher et al. (2020)

Deliberate cold exposure is the best way to recruit brown fat

In addition to being the first study to discover the beneficial relationship between brown fat and blood pressure, the Becher et al. findings confirm two things that we already knew:

  1. Cold exposure activates and recruits brown fat. Because the researchers reviewed thousands of PET scans made available by the Memorial Sloan Kettering Cancer Center in New York City, they were able to compile a robust dataset comparing the prevalence of brown fat to the average monthly temperature on the date of the scan. Unsurprisingly, brown fat increased during colder months, confirming findings in smaller cohorts that show brown fat activation in Danish winter swimmers (e.g., Søberg et al. 2021).

  2. Americans generally lose brown fat as they age. Although it has long been understood that human babies are born with ample stores of brown fat to facilitate thermoregulation under extreme weather conditions, until 2009 brown fat could not be detected in adults, and most medical professionals believed it was completely lost in maturity. Only after advancements in PET technology allowed imaging of brown fat did definitive evidence emerge that, despite the tendency for brown fat to decline with age, it could be retained into adulthood, and correlated with regular cold exposure. This new study compiles the largest data set ever showing that the percentage of adults with detectable brown fat declines with age, from almost 60% at age 20 years, to as little as zero after age 90. (The study does not answer whether the decline is a cause of ageing, or an effect).

Hormesis looks like a contradiction

These two contrasting findings -- that deliberate cold exposure can cause high blood pressure in the short term, but be associated with lower blood pressure in the longer term -- might seem counter-intuitive except for the fact that the principle of hormesis suggests brief periods of stress can be good for our health. It is the principle of hormesis that inspired the title of Scott Carney's book about Wim Hof's incredible accomplishments of human endurance, What Doesn't Kill Us (Carney 2017).

However, long before I met Carney, I was introduced to the principle of hormesis through Nassim Nicholas Taleb's book Antifragile (2012). In my role as an Associate Professor of Engineering at Arizona State University, I study infrastructure resilience during disasters, and Taleb's idea that living systems can grow stronger under stress is an important philosophical underpinning in my field of research.

In Antifragile, Taleb pointed out that only machines benefit from constancy. Living things benefit from variation.

Machines benefit from constancy. Human beings benefit from variation.

For example, we put pretty much the same gasoline into our cars every time we fill the tank. However, if we thought of food as "fuel" for our metabolic "machines," not only would we wind up eating the same thing at every meal, but the metaphor would lead to dangerous misconceptions about how we should be caring for ourselves. Conversely, what is bad for automobiles can be very beneficial for human beings.

An emerging movement in medicine emphasizes a restoration of the naturalistic rhythms and variation that have been removed from modern, industrial life. To avoid the constancy of an injurious, machine-like existence, we must re-introduce to our lives the kind of irregular stressors that our ancestors could not avoid.

The medical term for antifragile is hormesis.

Hormesis is a fundamental concept in evolutionary theory. From the beginning through the present time, life on earth has existed in harsh environments in which cells are often exposed to free radicals and toxic substances. To avoid extinction organisms have developed complex mechanisms to cope with the environmental hazards. - Mattson (2008)

The concept of hormesis was originally emerged in toxicology to describe the potential benefits of small doses of what would would be poisonous in larger quantities. For example, in my toxicology in graduate school, I was taught that there is no safe dose of radiation -- i.e., that any dose of radiation would increase mortality.

It turns out, that's not true. In fact, radiation that can be deadly in high doses can be beneficial at low doses -- and this principal applies to many different types of stressors.

In some, but not all cases, exposure to a low dose of an agent or condition that is toxic at higher doses induces an adaptive, potentially beneficial effect on the cell or organism if exposed to a subsequent and more massive exposure to the same or related stressor agent, a phenomenon called preconditioning in the biomedical sciences. Such adaptive responses to low doses of a stressor that is toxic at high doses have been observed in essentially all organisms studied so far, including prokaryotes, fungi, plants, invertebrates and mammals, including humans. - Calabrese et al. (2007)

Hormesis has been recognized as critical to health for hundreds, if not thousands, of years, albeit under different names including: preconditioning, inoculation, and exposure therapy. For example, in 'Stress Inoculation' I wrote about the concept of eustress, compared with distress, and I cited Stanford Professor Kelly McGonigal's realization that your beliefs about stress can be more dangerous than the stress itself (The Upside of Stress, McGonigal 2012).

McGonigal wrote that study subjects "who learned to view their stress response as helpful were less stressed out, less anxious, and more confident... ."

"In the typical stress response, your heart rate goes up and your blood vessels constrict, but in studies in which participants viewed their stress response as helpful, their hearts were still pounding but their blood vessels remained relaxed -- which is a much healthier cardiovascular profile." - McGonigal (2012)

The key to eustress is knowing the shape of the dose-response curve. The typical shape of a hormetic curve is an upside-down 'U.'

When you get too little dosage (of exercise, of micronutrients, of cold exposure, or of stress) your health will suffer. That is, a lack of stress can be harmful.

Add a little bit of dose, and health improves, but too much results in harm again. Optimum health is found in the middle part of the dose-response curve -- not too little, not too much.

While hormesis is most often thought of in the context of exposures to exogenous agents or environmental conditions, it should also be recognized that hormesis is integral to the normal physiological function of cells and organisms. - Mattson (2008).

Intermittent living?

While the concept of hormesis is finally reaching the medical mainstream (e.g., Calabrese 2018), two Dutch scientists coined a new term for adopting a hormetic approach to health called "intermittent living" (Pruimboom & Muskiet 2018). They describe four examples: thirst, hunger, temperature, and oxygen.

  1. Intermittent thirst is the practice of deliberately allowing yourself to feel "mild thirst," which they claim will reduce cortisol levels and "decrease anxiety, fear, and aggressive behavior."

  2. Intermittent hunger (fasting) is the practice of skipping meals to initiate autophagy of weak or damaged cells, promote mitochondrial health, and increase insulin sensitivity.

  3. Intermittent hot and cold exposure is the practice of incorporating sauna and ice bathes to stabilize metabolism, reduce blood glucose levels, guard against obesity, and promote mitochondrial proliferation.

  4. Intermittent hypoxia/hypercapnia is the practice of modulating blood oxygen and carbon dioxide levels to reduce inflammation, boost immune system function, slow ageing, and may ameliorate feelings of panic or anxiety.

The mechanisms by which intermittent practices operate are similar to the way exercising our muscles cam make them weak and sore at first, then prompt our body to recover during rest and soon become stronger. Thus, rest and recovery are as important to building strong muscles as is exercise.

The upside-down 'U' shape of the typical hormetic dose-response curve resolves the paradox of the ice bath and hypertension. That is, the intermittent living hypothesis suggests that a little bit of what looks bad for you in the short-term might actually be good for you in the longer-term.

Hypertension can be a serious disorder that escapes notice until it is too late. Screening for high blood pressure is inexpensive and may protect against mortal risk by motivating lifestyle changes or other interventions that prolong healthspan. The principle of hormesis suggests that extension of healthspan requires discomfort or inconvenience in the short term, in the pursuit of longer term health goals.

Nonetheless, I can't give you medical advice, nor tell you whether deliberate cold exposure is a good choice for you, because I'm not your doctor and I don't know where your dose-response optimum resides.

Medical studies draw inferences and make generalities from a large ensemble of data, but none of the subjects in the study are you. That is, what is statistically true for the people in the study may not hold true for you. When it comes to an ice bath practice, there is no study that can substitute for your own experience, and monitoring of your own response.

What I can do is tell you more about what's been working for me:


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. Subscribe to for more information from Seager on taking charge of your own physical & mental health.

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