Episode 232: Cold Exposure for Mental Health
Liam Browning, Brandon Luu, MD, Nicholas Fabiano, MD, David Puder, MD
Editor: Joanie Burns, NP
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Introduction
Cold exposure, a practice involving brief immersion in cold temperatures through showers, ice baths, cryotherapy, and cold-water plunges, has surged in popularity in recent years, due in part to advocates on social media such as Wim Hof.
Wim Hof (famously dubbed “The Iceman”) has built a global following with his extreme feats of cold endurance and his Wim Hof Method, which involves cold exposure with deep, rapid breathing practices. He asserts that cold immersion strengthens the immune system, helps regulate stress, and boosts mental clarity, all while training the body and mind to adapt to challenging conditions.
Other podcasters have amplified these claims and brought them into mainstream attention, often citing research on the potential for cold exposure to increase dopamine levels, improve mood, kickstart metabolism, and enhance mental toughness. To many, cold immersion is more than just a wellness trend—it’s now seen as a science-backed way to improve mental health (Czarnecki et al., 2024). In this podcast, we’ll dive into the science of cold immersion, separating fact from hype to evaluate its relevance for mental health and well-being.
Forms of Cold Exposure Available for Mental Health
The practice of cold immersion involves cold plunges, cold showers, cold-water swimming, and cryotherapy.
Cold water immersion: 5-15°C (40-59°F) for 2-15 minutes
Cold showers: <15°C (<59°F)
Cold water swimming <15°C (59°F)
Cryotherapy: -110 to -140°C (-166 to -220°F) for 2-4 minutes
Although many people choose to take cold showers daily, the thermal conductivity, or heat-transfer coefficient, is lowest for air (0.024 W/m·K), compared with water (0.58 W/m·K) and ice (2.1 W/m·K), meaning cold water and ice are about 25x and 100x more efficient at transferring heat, respectively, compared to air. This also explains why cryotherapy temperatures need to be so low.
However, ice is less effective at cooling than water because it does not adhere to the body’s contour to maximize surface area. Water also allows for convective cooling, where the movement of water molecules constantly circulates cold water to the skin.
Compare the length of time recorded by Guinness World Records:
Longest swim: Krzysztof Gajewski swam 3.7 miles in 1 hour and 46 minutes at 4.84°C (40.7°F)
Longest full contact with ice: 4 hours and 2 minutes by Lukasz Szpunar
History of Cold Therapy for Physical and Mental Health
The deliberate exposure to cold temperatures for therapeutic benefits has deep cultural and historical roots that date back to Greek and Roman times where it was used in bathhouses. It was also used medicinally during this time period, particularly by Hippocrates and Galen, the famous Roman physician who used cold water immersion for fevers and snow for bleeding. The practice has continued in Nordic countries where it remains an integral part of daily life. In Finland, for example, sauna use is sometimes paired with plunging into icy waters. This sauna-cold routine has been a cornerstone of Finnish wellness culture for centuries and has gained global recognition for its purported health benefits.
The Kuopio Ischemic Heart Disease Risk Factor (KIHD) Study (Laukkanen et al., 2018) discussed in our earlier episode on sauna (episode 221), highlights the profound health benefits of sauna practices.
The study followed thousands of Finnish men and found that almost daily sauna use is associated with reduced risks:
47% lower risk of hypertension
62% lower risk of stroke
66% decreased risk of dementia
37% reduced risk of pneumonia
78% reduced risk of a psychotic disorder
While the sauna itself plays a significant role, cold exposure might have also played a role in some of these health benefits. However, this study did not describe the extent to which subjects were engaging in cold exposure, and the epidemiological data on the practice is incredibly scarce. We contacted the authors of the KIHD study in Finland, Dr. Jussi Kauhanen and Dr. Jari Laukkanen, and they said the amount of cold exposure was not measured, and likely the practices varied between winter and summer and might be hard to measure in a cohort like this.
What Happens to the Body During Cold Exposure?
When the body is suddenly exposed to extreme cold, it initiates a “cold shock” response, which is essentially an acute stress response. This involves a coordinated surge of bottom-up signals from the body and top-down processing in the brain. At the core of this response are two main, interlinked systems: the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis. Together, they form a recursive feedback loop that influences arousal, decision-making, and the body’s capacity to adapt to stress. Notably, these same pathways are also activated by other intense stressors, such as vigorous exercise or life-or-death scenarios.
“Bottom up” signals from the body
Cold is detected by thermoreceptors of the skin that are sensitive to rapid temperature drops. This activates sensory nerve fibers that synapse onto the spinal cord and signal up to the thalamus and the hypothalamus in the brain.
The hypothalamus integrates these thermal signals and activates arousal centers in the brainstem and the spinal cord, activating the sympathetic nervous system.
The sympathetic nervous system signals the adrenals to release epinephrine (adrenaline) and norepinephrine (noradrenaline) into the bloodstream.
At the same time, the hypothalamus releases corticotropin releasing hormone (CRH), activating the HPA-axis and potentiating release of norepinephrine in the brain via the locus coeruleus.
“Top-down” signals from the brain and mind (Morris et al., 2020)
In anticipation of the cold and during immersion, our sensory cortices, prefrontal cortex (PFC), insula, and anterior cingulate cortex (ACC) constantly evaluate how much danger the cold plunge poses to us.
These converge onto salience and anxiety centers of the brain, such as the amygdala, which excite the locus coeruleus, the brain’s primary source of norepinephrine, and the hypothalamus, which increases CRH release and HPA-axis activity.
In turn, the increased norepinephrine and CRH heighten our arousal and narrow our attention to help us make fast decisions in the face of our perceived danger.
While the cold immersion continues and we attempt calm ourselves, we rely on the PFC to regulate the amygdala and hypothalamus, but the high levels of norepinephrine, CRH, and cortisol bias our thinking and our decision-making towards reflexive, survival based decisions, driving us to want to get out of the cold.
The end result:
Vasoconstriction: Blood vessels constrict to preserve core temperature, reducing blood flow to extremities.
Nerve conduction slows due to the cold, leading to a reduction in pain and sensation.
Heart rate: Typically increases at start, followed by a decrease. After exercise it might lead to a drop by cooling the body quickly.
Increase in systolic and diastolic blood pressure, sometimes as much as 20-40mmHg.
Increased respiratory rate: Breathing becomes rapid and shallow, sometimes gasping.
This is how many die when submerging in cold water.
Norepinephrine increases ~ 2-3 fold and remains elevated for hours.
Cortisol increases, but this may be for the unacclimated.
Shivering is maximal at core body temperature ~ 34–35°C (93-95°F).
Cold Water Swimming and its Benefits
Cold water swimming, a practice deeply rooted in Nordic traditions, is gaining global attention for its purported health benefits. Dr. Susanna Søberg, author of Winter Swimming, highlights its potential to improve metabolism through the activation of brown adipose tissue (BAT) and its mood-enhancing effects. These effects are commonly cited by enthusiasts and researchers alike, especially as initial studies of cold water swimmers showed positive effects on the metabolism, mood, and well-being (for review, see Kunutsor et al., 2024).
Several studies have assessed the effect of cold-water swimming on mood, most notable of which is a case report of a 24-year-old woman with treatment-resistant depression who took up weekly open-water swimming off the coast of England and had complete remission of symptoms without medications (van Tulleken et al., 2018). It should be noted that this patient swam from April-September, not in the winter.
However, as with other cold immersion practices, the evidence remains limited. These initial studies lack adequate controls, sometimes lacking control groups entirely, have small sample sizes, have limited replicability, and do not account for confounding factors like physical activity, socialization, healthy user bias, and the calming effects of natural environments. Thus, to disentangle the mechanisms of cold exposure, we need to focus on passive methods of cold exposure.
Cold Therapy Improves Mood
Multiple studies have shown an improvement in mood immediately after cold-exposure:
Kelly and Bird, 2021: Improved mood following a single immersion in cold water:
42 participants stood in chest-deep 13.6°C (56.48°F) sea water in the UK in November for up to 20 minutes.
Compared to the 22 controls, the cold water group experienced small but significant improvements on all Short Form of the Profile of Mood States (POMS-SF) subscales immediately after cold water exposure.
Overall, 15 point decrease (51 to 36) for cold water vs. 2 point decrease (42 to 40) in the control group.
Vigor by 1.1, and Esteem-Related Affect by 2.2 points Tension by 2.5, Anger 1.25, Depression 2.1, Fatigue 2.2, and Confusion 2.8 points.
Control group increased in depression by 1 point.
The maximum score for these subscales ranges from 16-32.
Note. Reprinted from “Improved mood following a single immersion in cold water”, by Kelly, J. S. & Bird, E. (2022). Lifestyle Medicine, 3(1), e53.
Yankouskaya and colleagues 2023: Short-Term Head-Out Whole-Body Cold-Water Immersion Facilitates Positive Affect and Increases Interaction between Large-Scale Brain Networks:
33 participants sat in mildly cold 20°C (68°F) water up to their clavicles for 5 minutes
Immediately after immersion, positive affect increased and negative affect decreased according to [the Positive and Negative Affect Schedule] PANAS by about 5 points each.
Participants also felt more active, alert, attentive, inspired, proud, and less nervous.
Cold water immersion correlated with brain activity changes on fMRI scans, specifically, with increased coupling of the mPFC with the anterior insula and dlPFC and decreased coupling between the mPFC and the ACC. Of note: Mechanistically, aberrant functional connectivity between these nodes has been linked to various depressive symptoms (Sheline et al., 2010).
Four connections were uniquely correlated with self-reported changes in positive affect after cold-water immersion: between DMN.MPFC; two nodes of the salience network (ACC and RPFC-L); and between FP.PPC, DAN.IPS, and Vis.Lat in the right hemisphere. Notably, a recent study identified these same regions of the salience network (dlPFC and ACC) to be larger in depressed patients compared to healthy controls (Lynch et al., 2023).
Note. Reprinted from “Short-Term Head-Out Whole-Body Cold-Water Immersion Facilitates Positive Affect and Increases Interaction between Large-Scale Brain Networks”, by Yankouskaya, A. et al., 2023, Biology, 12(2), p. 211.
Reed and colleagues 2023: Cardiovascular and Mood Responses to an Acute Bout of Cold Water Immersion:
Sixteen adults immersed for 15 minutes in 10°C (50°F) water up to the sternum (they did not cover with cold water the cervical sympathetic chain of the sympathetic nervous system surrounds the jugular area in the neck).
Assessments were conducted pre-immersion, during immersion (1-minute and 15-minute time points), 30 minutes post-immersion, and 180 minutes post-immersion.
Negative affect (assessed via PANAS) decreased significantly only 180 minutes post-immersion (p < 0.001), but not during or immediately after immersion. Positive affect did not change.
However, for the negative affect, this may be due to one participant responding well (see box plot below)
Note. Reprinted from “Cardiovascular and mood responses to an acute bout of cold water immersion”, by Reed, E. L. et al., 2023, Journal of thermal biology, 118, 103727.
Serum cortisol levels did not change from 0 minutes to 30 minutes but decreased by 47% at 180 minutes (p = 0.014).
No significant changes in β-endorphin levels were observed throughout the protocol.
Cold Exposure Increases Dopamine and Norepinephrine in the Body: The Catecholamine Hypothesis
The anecdotal improvements in mood in those observed in these studies may be due to increases in catecholamines, as first demonstrated by a study in 2000 by Sramek and colleagues, Human physiological responses to immersion into water of different temperatures:
10 male subjects sat in a chair in different temperatures of mildly cold water for 1 hour.
32°C, 20°C, and 14°C (90°F, 68°F, 59°F respectively).
Plasma norepinephrine, dopamine, epinephrine, and cortisol levels were checked sequentially at 0, 30, 60, 120 minutes.
The coldest temperature dropped rectal temperatures from 37.3°C to 35.6°C and increased metabolic rate by 350% while also mildly increasing HR, SBP/DBP.
Plasma peripheral (not in the brain) norepinephrine and dopamine each increased 5-fold during immersion in the coldest water, while epinephrine remained unchanged.
Plasma cortisol decreased in each session, including in control sessions, which may suggest psychological-mediated elevations in cortisol that decreased as the participants became used to intervention.
Note. Reprinted from “Human physiological responses to immersion into water of different temperatures”, by Šrámek, P. et al., 2000, Eur J Appl Physiol, 81, pp. 436–442.
Meanwhile, a more recent study by Eimonte and colleagues (2021) showed that norepinephrine, epinephrine, and cortisol can increase with shorter cold-plunge sessions. In this study, 12 young men sat in mildly cold 14°C (59°F) water for 10 min. Cortisol (ηp2 = 0.22), norepinephrine (ηp2 > 0.4), and epinephrine (ηp2 > 0.5) were each significantly increased and remained elevated for several hours after immersion.
Note. Reprinted from “Residual effects of short-term whole-body cold-water immersion on the cytokine profile, white blood cell count, and blood markers of stress”, by Eimonte, M. et al., 2021, International Journal of Hyperthermia, 38(1), 696–707.
Leppäluoto and colleagues (2008) investigated the effects of repeated cold exposure over 12 weeks in 20 female participants, comparing 3x weekly cold water swimming (0–2°C for 20 seconds) and cryotherapy (-110°C for 2 minutes). The study found that plasma norepinephrine increased 2-3 fold acutely after each session for both interventions, and this effect persisted throughout the 12-week period.
In contrast, changes in epinephrine and adrenocorticotropic hormone(ACTH) levels were minimal. Cortisol levels peaked during the first two weeks of cold-water swimming before declining by week 4, indicating habituation to the stressor. It’s unclear to what extent the habituation is a result of psychological or physiological adaptation. Meanwhile, pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α remained unchanged.
Note. Reprinted from “Effects of long‐term whole‐body cold exposures on plasma concentrations of ACTH, beta‐endorphin, cortisol, catecholamines and cytokines in healthy females”, by Leppäluoto, J. et al., 2008, Scandinavian Journal of Clinical and Laboratory Investigation, 68(2), 145–153.
This suggests that norepinephrine will likely continue to increase during cold exposure even after a person becomes cold-adapted. While the increases in norepinephrine suggest a plausible mechanism for the enhancements in mood and feelings of alertness and have been touted by social media influencers, there has only been one RCT assessing repeated cold exposure on depressive symptoms:
A Randomized Control Trial of Cold Therapy on Depressive Symptoms
Rymaszewska and colleagues (2020): Efficacy of the Whole-Body Cryotherapy as Add-on Therapy to Pharmacological Treatment of Depression—A Randomized Controlled Trial:
Methods
92 adults (aged 20–73 years) with a diagnosis of mild-moderate depression (17 on HAM-D and 21-24 on BDI) who were receiving outpatient therapy.
Participants were randomly allocated and exposed to cryogenic temperatures −110°C to −135°C (the experimental group (EG)) or to low, but not cryogenic temperatures −50°C [the control group (CG)].
10 3-minute sessions across 2 weeks (Mon-Fri).
Results
Both groups improved on the HAM-D and BDI.
There were no differences between groups on either of these metrics by the end of the study.
BDI only differed between the two groups 1 week after treatment, when the cryotherapy group scored an average of 9 points lower on BDI compared to the control group (decrease from 21.7 to 9.4 in cryotherapy group vs. 24 to 18.6 in control group).
This effect was not maintained after 2 weeks of treatment or after 2 week follow up (cryotherapy group increased to 15.2 vs. controls 18.1).
However, cryotherapy participants reported statistically significant improvements in several items on the BDI.
Sadness, loss of pleasure, self-criticalness, loss of interest, and indecisiveness.
The cryotherapy group also had significantly lower scores on the cognitive-affective dimension and the somatic dimension.
Cryotherapy participants also improved more on quality of life and other symptoms related to pain, sleep, and self-acceptance.
There were no changes in inflammatory markers (CRP, IL-6, IL-10, NO) or antioxidative stress.
Central vs. Peripheral Catecholamines: Does cold exposure increase levels of dopamine in the brain?
Dopamine, a neuromodulator associated with mood, motivation, and reward, has garnered significant attention in discussions about cold exposure. While there is some evidence, such as the Sramek and colleagues (2000) study, suggesting a substantial increase in plasma dopamine levels following cold water immersion, it is important to note that this finding does not necessarily translate to increased dopamine activity in the central nervous system. Mechanistically, peripheral increases in dopamine do not translate into an increase in central dopamine levels. The blood-brain barrier is highly selective and restricts the passage of many substances from the bloodstream. Dopamine is relatively polar and is actively blocked by efflux transporters at the blood-brain barrier, preventing any significant entry (Abbott et al., 2010). As an example, for people with Parkinson’s Disease (low dopamine centrally), simply administering dopamine peripherally does not increase central levels. Instead, L-DOPA (levodopa), a precursor of dopamine, is used, since it can cross the blood-brain barrier (Oertel et al., 2016).
In rodents, chronic cold exposure leads to an adaptive reduction in central dopamine, likely to attenuate the dopamine system to subsequent stressors (Moore et al., 2001 & Valenti et al., 2012). Rodents exposed to acute stressors such as tail shock, foot shock or restraint exhibit marked increases in extracellular DA levels in the mPFC and moderate increases in the NAc and/or striatum (Moore et al., 2001); however, no studies exist measuring the effect of acute cold exposure on central dopamine levels or on reward-related activity in the brain. It’s unclear whether these stress-related increases in dopamine are linked to reward or represent a separate mechanism linked to aversive stimuli (Holly & Miczek. 2016). Because cold exposure in animal studies is involuntary—and, from the rodent’s perspective, likely torture—its relevance to human experiences is limited. Humans who deliberately engage in cold water immersion often view it as a personal challenge to overcome, a process that can itself elevate dopamine via a sense of reward. Thus, data from animal models of forced cold exposure may not readily translate to the human context in which belief in the health benefits could amplify–or lead to–a dopaminergic response.
Meanwhile, peripheral norepinephrine released from the adrenals is also not thought to cross the blood-brain barrier, but, unlike dopamine, peripheral norepinephrine is likely associated with increased norepinephrine in the brain in response to a stressor. This is due to the hypothalamus’s parallel actions on increasing activity of the locus coeruleus (via CRF) and the sympathetic nervous system, as well as the influence of baroreceptors on the locus coeruleus (Van Bockstaele et al., 2001). While no human studies have measured central norepinephrine in humans in response to stress, animal models show that the amount of central norepinephrine and the activity of locus coeruleus neurons increase in response to various forms of stress, including foot shock, restraint, and auditory stress (Valentino & Bockstaele, 2008). There is some evidence of chronic cold exposure (5°C [41°F] cold room for multiple days/weeks) altering locus coeruleus activity and extracellular norepinephrine in the brains of mice (Jedema et al., 2001; Buffalari & Grace, 2009), but there are no studies assessing acute cold exposure on brain norepinephrine in animals.
Notably, exercise can increase plasma norepinephrine by 1.5-6x, depending on the intensity (Zouhal et al., 2008). Meanwhile, medications such as SNRIs affect plasma concentrations less due to their selectivity for norepinephrine, serotonin, and dopamine transporters in the brain.
Cold Exposure on Inflammation and Immune Functioning
Although this cryotherapy study did not show a direct effect on inflammation, many proponents of cold exposure, particularly Wim Hof, argue that it improves inflammation and immune functioning. A self-report survey in 1999 by Siems suggested that cold water swimmers experience 40% less upper respiratory tract infections than those who don’t engage in cold water swimming. A study of Wim Hof and some of his followers also showed a reduced pro-inflammatory cytokine response (IL-6, TNF-alpha) to injected bacterial endotoxin (Kox et al., 2014). Wim Hof also claims cold exposure increases WBCs, and although there is a theoretical basis of the enhanced immune response (as norepinephrine and cortisol are thought to mobilize WBCs in states of sympathetic arousal in preparation for defense of microbes associated with potential bodily injury), the results of studies in winter swimmers and in those engaging in passive cold water immersion are limited. For example, some studies show an increase in pro-inflammatory plasma IL-6 concentration and monocytes in cold water swimmers (Dugué & Leppänen, 2000; Lombardi et al., 2014) and with passive cold water immersion (Janský et al., 1996; Brazaitis et al., 2021). However, these studies were small, heterogeneous, and lacked adequate controls, and the in vivo significance of these findings and whether they are clinically relevant have not been studied adequately (Tipton et al., 2017).
There are no studies, to our knowledge, that assess changes in inflammatory cytokines in participants who have elevated cytokines at baseline, which represents a possible ceiling effect observed in current studies.
The anti-inflammatory effects of cold exposure are also questionable for exercise-induced inflammation, as a recent systematic review and meta-analysis of some low-quality cold water immersion studies showed no effect on post-exercise inflammatory markers (IL-6, CRP, IL-10) and a small positive effect for reducing exercise-related delayed onset muscle soreness (DOMS) (Xiao et al., 2023). Nevertheless, as we’ll discuss later, anabolic signaling, which relies on inflammatory signaling processes, is significantly decreased by cold exposure, suggesting cold exposure could have an impact on local inflammation.
How Cold Therapy Affects the Mind: Mindfulness, Overcoming Challenges, and Dissociation
There are very few studies on the topic, but a qualitative study (Østergaard et al., 2024) did identify mindfulness as a key theme expressed by Danes who were frequent cold water swimmers:
It can be quite meditative to sit there in the water. You quickly forget other things and have a strong focus on being present in the moment, because it’s challenging to think about other stuff when you’re getting hit with that cold water constantly. So, I don’t think much is happening in your head.
Sometimes it can be challenging to sit and meditate and not think about anything. But when you get into the cold water, you just can’t think about anything else. It’s like the body, with the cold and warmth just forces you to be in the moment.
From our own experience, the first seconds in the water can be profoundly overwhelming, as the shock of the cold water abruptly brings attention to the body's physiological responses. A heightened sense of panic may arise, accompanied by rapid breathing and an intense urge to escape the situation. However, by consciously regulating one’s breathing and enduring the discomfort, a state of calmness gradually emerges. This experience of pushing through the discomfort is echoed by Andrew Huberman, who advises to push through multiple of these “walls,” as this can help train willpower and resilience.
Patients with borderline personality disorder often do grounding tasks within dialectical behavioral therapy, including holding ice. For many patients, this can be something that deters self-harm behavior.
However, studies have shown that cold can increase dissociation acutely (beyond a certain temperature and duration), likely as a way to protect ourselves from the pain. A study of the cold pressor task (holding your arms under freezing water for as long as you can) showed small increases in dissociation symptoms (peritraumatic dissociative experiences scale ([PDES]; t(69) = 4.87, P < 0.01, partial η2 = 0.26), but those with high trait dissociation (>25 on dissociative experiences scale [DES]) did not experience more dissociation than those with low trait dissociation (<10 on DES). (Giesbrecht et al., 2008). A repeat similar study found that pain catastrophizing was a much stronger predictor of how much someone would dissociate during this cold pressor task, compared to anxiety sensitivity and depression symptoms (Gómez-Pérez, et al., 2013).
Anxiety Sensitivity (AS): predicted 5% of the variance in laboratory-induced dissociation.
Depressive Symptoms: predicted 4.4% of the variance in laboratory-induced dissociation.
Pain Catastrophizing: predicted 18.6% of the variance in laboratory-induced dissociation, highlighting its role in how stress is appraised.
It would be interesting to have another arm of this study type where participants are told that doing this would decrease dissociation and improve mental wellbeing. Perhaps from that arm, the “meaning” would change the appraisal of the stress, and the pain would have meaning and less dissociation. This change in meaning is reminiscent of what Viktor Frankl observed as a common thread in those that suffered in the concentration camps (see episode 113):
The way in which a man accepts his fate and all the suffering it entails, the way in which he takes up his cross, gives him ample opportunity—even under the most difficult circumstances—to add a deeper meaning to his life. It may remain brave, dignified and unselfish. Or in the bitter fight for self-preservation he may forget his human dignity and become no more than an animal.
Future studies should address how cold exposure acclimatization changes the stress response and the degree of dissociation someone experiences. Furthermore, as we discussed in episode 230 in the written section titled “The Psychological Antidepressant Mechanisms of Exercise”, there is a benefit of “mastery experiences” as key sources of self-efficacy, in which enduring challenges and increasing one’s capabilities can improve how they feel about themselves. There might be an increase in self-efficacy from progressive cold exposure, which improves things like dissociation and mood.
Is Cold Exposure Just Placebo?
Generally, it also needs to be considered that few studies use a control arm that could benefit from the placebo effect.
An interesting study assessed the effect of 21 days of the Wim Hof Method (30-second to 3-minute cold showers plus rapid breathing) vs. active control (warm showers and slow breathing) in 78 mildly depressed (PHQ score 10-20) women (avg age 45) (Blades et al., 2024). Both groups experienced a 20-30% reduction in depression (CES-D) and anxiety (GAD-7) symptoms but with no differences between groups. However, due to the different breathing patterns and different temperatures, it is difficult to isolate the effect of cold exposure. Also, the showers might not have been cold enough to cause a robust physiological response, potentially making the breathing a more important factor. Given both groups engaged in an intervention, the rate of spontaneous remission can’t be ruled out with the current study design.
(Depressive symptoms)
Note. Reprinted from “A randomized controlled clinical trial of a Wim Hof Method intervention in women with high depressive symptoms”, by Blades, R.et al., 2024, Comprehensive psychoneuroendocrinology, 20, 100272.
Broatch and colleagues (2014) attempted to control for the placebo effect by comparing cold water immersion to immersion in room temperature water and immersion in room temperature water with an added skin cleanser. The participants were told the skin cleanser was beneficial for improving post-exercise recovery. Results showed that only the control group without the added skin cleanser had a reduction in leg strength and subjective ratings of readiness for exercise, pain, and vigor 48 hours after completing a HIIT session.
This raises an important need for future cold immersion studies to measure and control for expectancy effects when evaluating treatment outcomes. Research in other areas of psychiatry, such as the antidepressant effects of psychedelics, has demonstrated that belief in a treatment’s efficacy can significantly moderate outcomes. For instance, psychedelics only show superiority over traditional antidepressants when participants believe in their therapeutic potential (Dutcher & Krystal, 2024).
The Theoretical Mechanism Behind Cold Therapy’s Beneficial Effects on Mood
Engaging in consistent, challenging activities that elevate norepinephrine and dopamine levels—such as cold exposure and exercise—may theoretically recalibrate the signal-to-noise ratio within fear and anxiety-related neural circuits that activate the stress response, thereby reducing anxiety through bottom-up mechanisms. However, it is less clear whether these activities influence top-down cognitive processes, such as the tendency to misperceive threats or maintain negative self-perceptions. Addressing these cognitive biases appears to require targeted psychotherapeutic interventions.
Takeaways on the Antidepressant Effects of Cold Exposure
There are very few studies assessing the effect of cold exposure on depressive symptoms.
Mood improves immediately during and following cold exposure.
Norepinephrine is consistently increased during cold exposure and can persist for several hours.
Increases in cortisol during cold exposure may reflect psychological stress, as this effect decreases with repeated exposures.
Cold exposure likely has a small, undetermined effect on the immune system.
There are undoubtedly psychological mechanisms of the mood improvements of cold exposure, but not enough trials measure them or adequately account for placebo effects.
Cold Exposure Improves Post-Exercise Soreness, Power, and Strength
Currently, the most robust evidence for cold therapy is in improving post-exercise recovery. As previously mentioned, the strongest evidence for cold-water immersion is for improving delayed onset muscle soreness (DOMs) (24 h: SMD -0.34, 95%CI [-0.65, -0.04], 7 trials) the following day, according to a meta-analysis of 7 studies. However, rates of perceived exertion were unchanged at 24 and 48 hours. There was also a small effect of improving power recovery 24 hours after cold-water immersion (24 h: SMD 4.77, 95%CI [2.12, 7.42] 4 trials) as measured by the countermovement jumps and sprints (Xiao et al., 2023). It should be noted that many studies used different protocols of cold exposure, including the exercise selection, method of cold exposure, temperature, and duration.
For cold water immersion, colder temperatures have not been shown to provide additional benefit for muscle soreness, as a recent review of 44 studies found that studies using severe cold (5-9°C) and moderate cold (10-15°C) were similarly efficacious (SMD =.99 and 1.0 respectively) when compared to control (Batista et al., 2023). Interestingly, when stratifying studies by time of immersion, only studies of short (<10 min) or medium (11-15 min) duration showed a reduction in DOMs compared to control, while longer immersions (>16 min) was not statistically significant (SMD 95% CI [-.16, 1.65], but this may be a result of publication bias.
Interestingly, the previous meta-analysis by Xiao and colleagues showed a reduction in creatine kinase and lactic acid, markers of muscle damage and metabolism, at 24 and 48 hours after cold-exposure. However, muscle damage is thought to be a key mediator of muscle growth. Cold therapy may actually dampen the anabolic response to training by limiting muscle damage and by suppressing muscle protein synthesis and mTOR signaling (Peake et al., 2020).
In a 12-week trial of 21 men, after each strength training session, participants were randomized to 10 minute cold-water immersion up to the waist (10.1°C) or 10 minute active recovery on an exercise bike. The cold-water immersion group grew significantly less muscle (d = −4.1; P < 0.001) and their muscle fibers had less myonuclei, which are thought to increase growth factor secretion in response to exercise-induced inflammatory signaling (Roberts et al., 2015).
These findings were replicated in another study by Fyfe and colleagues (2019), showing that cold-water immersion up to the sternum (15 min at 23°C) blunted muscle gains to a 7-week training program compared to controls who sat in a chair. Endurance and muscle strength were unchanged.
Meanwhile, there are only five studies assessing the effect of cryotherapy on training adaptations, with mixed but limited findings thus far (Haq et al., 2022).
Cold Exposure and Brown Fat: Separating Hype from Science
Brown fat, or brown adipose tissue (BAT), is a subtype of fat tissue with many mitochondria that give the fat a more gray/brown hue. The mitochondria of brown fat are unique because they have an uncoupling protein that allows the brown fat to use glucose and other fat molecules to generate heat. This heat generating capability is vital for babies, as they cannot shiver.
Some studies have shown that brown fat can increase in activity in response to cold (Søberg et al., 2021), thus many advocates of cold-exposure claim that this increase in metabolic activity can be beneficial for metabolism and longevity.
However, this study by Søberg had major limitations:
Group similarities:
Both did around the same total physical activity/training per week, same plasma glucose, same cholesterol.
Differences in groups:
Total fat % was lower in the winter swimmer group (12.0% vs 18.2%).
This means the winter swimmers at the same BMI had more muscle potentially and less fat to insulate body heat, necessitating more heat production through brown fat.
The reported 500-calorie difference in daily resting energy expenditure is based on an extrapolation from measurements taken during a 30-minute cooling session using calorimetry. During this session, researchers observed a 10 calorie difference between the two groups. When this small difference was scaled to a full day, it resulted in the reported figures of 3,044 calories in the cold water swimmers versus 2,560 calories in the controls. However, it’s important to note that this difference in energy expenditure occurs only during the cooling period. Therefore, to achieve the reported benefits of BAT, one would need to remain cold consistently throughout the day.
Even if the authors were able to detect a true difference in 10 calories, which itself could reflect measurement variability of their calorimetry setup, it is not tenable to assume all of these calories can be contributed to BAT. The authors themselves state “the difference in cold-induced energy expenditure could not be explained by differential glucose tracer uptake in BAT between groups, also arguing for additional contributors in cold-induced thermogenesis.”
Where these claims continue to fall short is that BAT is incredibly sparse in adults, even in cold swimmers. It may be only 50-300g (about 1 pound) in the average adult and is only detectable in less than half of people. BAT is detectable more often in the winter, in women, in younger people, and in people with less adiposity (Au-Yong et al., 2009; Saito et al., 2009). This likely correlates with the amount of time someone feels cold.
The total energy expenditure of active BAT is incredibly small, on the order of 2-5% of basal metabolic rate (van Marken Lichtenbelt & Schrauwen, 2011). Assuming a total daily energy expenditure of 2000-3000 calories, of which basal metabolic rate is about 60%, this would equate to 40-90 calories/day. This pales in comparison to the brain, which accounts for about 20% of basal metabolic rate, and to skeletal muscle. The authors state “the improved glucose clearance following cold acclimation in humans is likely mediated, at least partly, by more efficient insulin-mediated glucose uptake by the skeletal muscle.” Consider how much glucose is taken up by muscles after a meal. It’s thought that muscle takes up 80% of postprandial glucose.
Cold exposure is thought to only increase the activity in brown fat, unlike dinitrophenol (DNP), a fat loss drug used in the 1920s-30s and by some bodybuilders today, which uncouples mitochondria in all tissues. While DNP increases energy expenditure by 30-40% and leads to weight loss by about 1lb/week, it has an incredibly low therapeutic index, as you can imagine disrupting mitochondrial functioning in the heart and brain can lead to devastating consequences (Cutting et al., 1933; Ost et al., 2017). Of note, there are currently phase II clinical trials investigating different prodrugs of DNP for use in type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD).
Does Cold Water Swimming Decrease Insulin?
Another frequently cited mechanism by which cold exposure improves metabolism is its potential to enhance insulin sensitivity and lower fasting insulin levels. For example, a study by Gibas-Dorna and colleagues (2016) investigated the effects of repeated cold water swimming on fasting insulin levels over seven months in non-obese female swimmers. In the cold exposure group, fasting insulin levels significantly decreased from 8.98 ± 2.29 µIU/mL in October (average water temperature 9.5°C or 49.1°F) to 6.82 ± 1.17 µIU/mL in January (1.0°C or 33.8°F), representing a reduction of 2.16 µIU/mL. By April (4.4°C or 39.9°F), insulin levels had slightly risen to 7.43 ± 1.36 µIU/mL, but they remained lower than at baseline. Conversely, the control group of indoor swimmers showed negligible changes in fasting insulin, with levels averaging around 7.00 µIU/mL from October to January.
However, before concluding that cold water swimming alone meaningfully reduces insulin, it’s important to consider this study had major limitations. First, the cold water swimming group had significantly higher baseline levels of insulin than the control group, which complicates any comparisons between the two groups. Secondly, this study was an observational study that did not control for factors such as exercise frequency, dietary habits, or other lifestyle behaviors–important influences on insulin and leptin levels. This is especially relevant considering the cold water swimming group is a self-selecting population (participants of an outdoor swimming club) that likely already believes in the health benefits of cold water swimming and therefore is more likely to make other health-conscious changes. In other studies on exercise and diet, when participants begin to change their exercise or eating habits for the better, they will typically change the other as well. Lastly, the study did not specify how often the participants engaged in cold exposure (“twice a week, or more than twice a week”), and if cold exposure alone were the key driver of lower insulin, it would be logical to see a continued decrease in insulin levels from January to March, when water temperatures are typically at their coldest; the data, however, did not clearly establish that trend.
A few small studies on passive cold exposure in diabetic patients have also reported modest effects on improved insulin sensitivity and increased metabolic rate. These effects are thought to be largely driven by cold-induced shivering, which elevates energy expenditure and glucose uptake by muscles, functioning similarly to mild exercise. When shivering is suppressed, the effects on insulin sensitivity are reduced but remain statistically significant, likely due to increased sympathetic nervous system activity or mildly elevated glucose uptake by brown adipose tissue and muscle during non-shivering thermogenesis (Remie et al., 2021). While these studies suggest short-term improvements in insulin sensitivity and energy expenditure, the changes are relatively modest, have shown limited replicability from study to study, and pale in comparison to exercise. Furthermore, there are no randomized controlled trials that have convincingly demonstrated long-term benefits of cold exposure in lowering basal insulin levels or insulin sensitivity.
Cold Exposure Acutely Decreases Processing Speed and Executive Functioning
In a systematic review of 18 studies (eight studies of cold air exposure and 10 of cold water immersion) on cold exposure’s effects on cognitive performance, cold exposure was shown to induce an impairment in 15 out of the 18 experimental settings, both during cold exposure and in the minutes to hours after. Processing speed and executive function showed the more consistent impairment while working memory and attention showed contrasting results (Falla et al., 2021).
Safety/Precautions of Cold Exposure
Cardiovascular risks
Risk of ventricular arrhythmias with concurrent sympathetic/parasympathetic activation from the dive response (Shattock & Tipton, 2012)
Predisposing factors, such as long QT syndrome, ischemic heart disease or myocardial hypertrophy, may be necessary for fatal arrhythmias to evolve in absence of hypothermia.
Arrhythmias due to hypothermia
The risk is highest during the “afterdrop”
During cold water immersion, the blood vessels in the arms and legs constrict in order to shunt blood to the core bodily organs, leaving your arms and legs much cooler. When you get out of the cold water, peripheral vasoconstriction decreases and the cold and warm blood mix, leading to a drop in core temperature as much as 4°F.
Risk of worsening ischemia, angina
Increased sympathetic nervous system response during cold shock may place strain on the heart, similar to exercise, which can exacerbate ischemia.
Neurological risks
Cerebral perfusion pressure decreases due to rapid hyperventilation from the cold shock response, increasing risk for ischemic stroke.
Patients with autonomic dysfunction or thoracic spinal cord injury should avoid cold exposure.
Other conditions such as asthma and Raynaud’s are relative contraindications to cold exposure, due to the respective risks of asthma exacerbation and ischemia of the fingers.
Recommendations and Future Directions: A Call for Further Studies
Despite widespread claims on social media regarding the mood-enhancing and cognitive benefits of cold exposure, there are currently very few randomized controlled trials (RCTs) on the subject. Additionally, significant heterogeneity exists among studies and the practices promoted online, making it unclear what specific protocols—such as temperature, duration, or timing—are most effective for mood enhancement, muscle recovery, or other purported benefits.
From a practical perspective, if a patient has no contraindications and finds cold exposure enjoyable, it may be reasonable to support its continued use. The benefit-to-risk ratio appears favorable, as the potential benefits, although not well-defined, likely outweigh the relatively low risks and costs associated with the practice. Furthermore, the placebo effect should not be underestimated; activities that foster a sense of energy and vitality may positively impact other facets of daily life. Psychological factors, such as the enhanced self-efficacy derived from overcoming the discomfort of cold exposure, may also contribute to mood improvements. However, to date, no studies have directly investigated these potential mediating effects.
In future studies, an ideal RCT would have the following design:
Treatment population: 50 patients with moderate depression
Treatment frequency and duration: 5x/Week for 8 weeks (to allow for any epigenetic impacts, similar to medications)
Treatment arms: Cold exposure 45°F for 3-5 minutes vs. active controls who are in water that seems cold 67°F 3-5 minutes
Outcome: Depression (HAM-D), Anxiety (GAD-7), Self-Efficacy (GSE), Treatment Expectations (TEX-Q), measured at 2, 4, 8, and 12 weeks. Cortisol, norepinephrine, dopamine, pre-post immersion once weekly.
Cold therapy offers intriguing possibilities for mental health, with evidence suggesting mood elevation and potential antidepressant effects. While physiological changes, including increasing norepinephrine levels, may underlie some of these benefits, the psychological aspect of willingly embracing discomfort aligns with logotherapy principles, promoting meaning through overcoming challenges. The research remains in its infancy, with mixed results and limitations in study designs. Nevertheless, social media influencers espouse the benefits of such interventions on enhancing resilience and treating mental health conditions, which need to be evaluated critically before clinicians can incorporate this into practice. If you are interested in collaborating to launch a study exploring these effects in psychiatry, let’s connect to bring this idea to life and study this much needed topic.
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