Cold Therapy Basics

Evidence Review

Systematic Review and Meta-Analysis (Cain et al., 2025)

This 2025 systematic review in PLOS ONE is the most comprehensive analysis to date of cold-water immersion's effects on health and wellbeing in healthy adults [1]. The authors searched multiple databases and included randomized controlled trials involving adults aged 18 or older undergoing cold-water immersion — defined as cold shower, ice bath, or cold plunge at water temperatures of 15°C or below for at least 30 seconds. Eleven trials met inclusion criteria.

Key findings: stress reduction was statistically significant at 12 hours post-immersion, though not at immediate, 1-hour, 24-hour, or 48-hour timepoints. Inflammation markers showed a biphasic pattern — an acute increase immediately post-immersion (consistent with a hormetic stress response) followed by a subsequent decrease. Sleep quality and quality of life measures trended favorably in longer-term interventions. The authors concluded that cold-water immersion offers practical health applications for stress management and wellbeing, while noting that the evidence base is constrained by small sample sizes, limited RCTs, and lack of population diversity.

Narrative Review of Voluntary Cold Exposure (Esperland et al., 2022)

This 2022 review in the International Journal of Circumpolar Health surveyed 104 studies on voluntary cold-water exposure in humans [2]. The authors assessed effects across metabolic, cardiovascular, immune, and psychological domains.

On metabolism: multiple studies documented reductions in body adipose tissue, improvements in insulin sensitivity, and reductions in insulin resistance — suggesting a protective effect against cardiometabolic disease. On immune function: cold exposure increased peripheral catecholamine concentrations, enhanced leukocyte counts, and was associated with reduced infection incidence in some populations. On mood: swimmers reported elevated positive affect, decreased negative emotional states, and increased vigor following cold-water immersion. The catecholamine and endorphin surges provide a plausible neurochemical mechanism. The authors were appropriately cautious about firm conclusions given the generally small sample sizes and methodological heterogeneity across included studies, but characterized the overall evidence as pointing toward beneficial health effects.

Neurochemical Response to Cold Immersion (Srámek et al., 2000)

This foundational human physiology study measured plasma catecholamine, cortisol, and metabolic responses in healthy men during immersion in water at four different temperatures: 32°C, 20°C, 14°C, and 8°C [3]. Participants were immersed head-out for one hour at each temperature.

At 14°C, plasma noradrenaline increased by approximately 530% and dopamine by approximately 250% compared to thermoneutral conditions. At 8°C, responses were even more pronounced. The study also documented increases in metabolic rate (energy expenditure) proportional to water temperature, with shivering thermogenesis contributing substantially at the coldest temperatures. This paper established the neurochemical basis for the mood and alertness effects of cold immersion that subsequent research has built upon. The magnitude of catecholamine release is comparable to acute psychological stressors and moderate exercise, lending credibility to the reported subjective improvements in mood and energy.

Brown Fat Activation in Winter Swimmers (Søberg et al., 2021)

This 2021 study in Cell Reports Medicine used FDG-PET imaging to directly measure brown adipose tissue (BAT) activity and thermogenesis in experienced winter-swimming men compared to age- and BMI-matched controls [4]. Participants were men who had practiced regular cold-water swimming two to three times per week for at least two years, often combined with sauna use.

Winter swimmers demonstrated significantly higher cold-induced thermogenesis compared to controls. PET imaging showed that both BAT glucose uptake and supraclavicular skin temperature responses were enhanced in winter swimmers. The winter swimmers also had a lower thermal comfort zone — their bodies operated at a slightly lower baseline temperature and were more thermodynamically efficient. The study concluded that chronic intermittent cold exposure produces measurable adaptations in brown fat biology and thermogenic capacity, and that these adaptations are relevant to metabolic health. Limitations include the small sample size (n=10 per group) and the cross-sectional design, which cannot prove causality.

Breathwork, Cold Immersion, and Mental Health (Czarnecki et al., 2024)

This 2024 case-control study compared mental health outcomes and upper respiratory tract infection (URTI) duration across three groups: those practicing cold-water immersion alone, those combining cold immersion with structured breathwork and stretching, and matched controls [5]. Using validated questionnaires for depression, anxiety, mindfulness, and somatic complaints, the cold immersion group scored significantly better on most mental health indices than controls. The combined breathwork and cold immersion group showed further improvements over the cold immersion-only group.

URTI duration was shorter in the cold immersion group compared to controls, and shorter still in the combined practice group. The case-control design and internet-based recruitment limit causal interpretation, but the study adds to a pattern of consistent findings linking regular cold-water exposure to reduced illness burden and better psychological functioning. The breathwork synergy finding aligns with the Wim Hof Method literature, which combines controlled hyperventilation with cold exposure and has documented immune-modulating effects in small experimental trials.