A popular belief is that cold temperatures can make you sick. However, there is still much debate among researchers whether this belief holds any merit and remains to be established (1, 2). Despite this disagreement, contemporary research has started to identify benefits associated with cold exposure and suggests that avoidance of cold temperatures does not guarantee immunity from sickness. These effects may be driven by the body’s physiological responses to the cold that allows for desirable outcomes. Namely, it may help with immune system function, waking up, and reducing muscle soreness. This article will examine the research investigating these claims.
Cold exposure’s effect on the immune system
Contrary to popular belief, cold exposure could help with issues related to sickness. It is important to note that cold temperatures have demonstrated a relationship with sickness and this topic remains to be understood (2).
Other research has indicated otherwise, proposing that cold exposure therapy can be beneficial in fighting against sickness. For example, a study using one-hour cold water immersion found it activated the immune system to a slight extent and increased antibodies that defend against sickness (3). While this study was only for 6 weeks, even one-hour cold exposure can elicit such effects and remains to be elucidated whether prolonged continuation of the practice can further enhance immune system functioning.
Similarly, in a study of 3018 participants, those who did cold exposure for 30 days with a duration of 30, 60, and 90 seconds had a 29% reduction in sick days for work compared to those who did not engage in cold exposure (4). It may be the case that these beneficial effects could also be driven by an increase in testosterone – a primary sex hormone that has been shown to stimulate the immune system (5). Although the evidence is still unclear as one study reported a decrease in testosterone after a single session of cold exposure, another reported an increase with repeated cold exposure (6, 7).
Based on the evidence provided, it remains to be clarified whether cold exposure is a valid therapy against sickness. Should cold exposure be perceived as beneficial, the mechanisms underlying its effects are yet to be determined but it is recommended that it should be incorporated into a consistent routine to receive its benefits.
Cold exposure’s effect on sleep
Upon waking up, many people report having sleep inertia – a transitional state accompanied by feelings of sleepiness, grogginess, and dread to start the day (8). This may be driven by sleep-related issues that are common among the general population, like insomnia as characterized by decreased sleep initiation, duration, consolidation, or quality (9). It is estimated that 10%–30% to even as high as 50%–60% of people have insomnia and is expected to get worse (10, 11). Negative outcomes of poor sleep have been widely established which can include a range of health complications and lower energy levels (12).
While sleep should be a priority, the data provided would suggest that having good sleep is not always guaranteed. However, some methods such as cold exposure can be implemented which can mitigate the symptoms associated with poor sleep to an extent.
In the previously mentioned study of 3018 participants, those who did cold exposure reported an increase in perceived energy levels with 91% of them intending to continue the routine (4). While the mechanism behind this enhanced energy effect remains unclear, it is reported that there are greater cortisol and norepinephrine concentrations – hormones that are thought to enhance energy and alertness, respectively (13, 14) – with cold exposure (3,15-18).
Additionally, cold exposure can also address the negative feelings of dread related to sleep inertia given that it is shown to release endorphins - chemical signals in the brain that produce positive emotions (19, 20). In summary, cold exposure should not be considered an alternative to sleep but can be used to alleviate poor sleep and is likely best utilized as a supplementary tool.
Cold exposure’s effect on muscle
Finally, cold exposure may reduce muscle soreness associated with workouts. Generally, muscle soreness is indicative of muscle damage – a requisite for muscle growth – but not always required (21, 22). Although, muscle soreness can negatively affect performance in the gym which could affect muscle growth (23). Cold exposure potentiates to be a useful application for mitigating muscle soreness and its related outcomes.
In a study comparing athletes receiving exposures either with cold water or warm water, perceptions of muscle soreness and general fatigue were significantly lower in the cold exposure group. Upon measuring differences between groups in subsequent physical performance, none were identified (24). It is important to note that this study was conducted on athletes and may not be representative of the general population. Lower muscle soreness and general fatigue may induce a psychological benefit in non-athlete populations that could be beneficial for their performance.
The mechanism underlying this effect may be due to reduced inflammation with cold exposure by decreasing blood flow to muscle tissues which lowers the likelihood of swelling in these cells (25). However, this inflammatory process is thought to be necessary for initiating biochemical reactions relevant to muscle growth (26). One study found that muscle growth was blunted but not strength following cold water exposure (27). Taken together, cold exposure is likely not optimal as a direct application technique to facilitate muscle growth. Nevertheless, if used to reduce muscle soreness, cold exposure may incur a psychological benefit that can allow one to have better training performance – which does have implications for muscle growth (22).
Conclusion
The benefits of cold exposure warrant further investigations to further understand its effects and mechanisms. Despite these contentions, it may be argued that cold temperatures – when conducted with established protocols – are not totally detrimental to one’s health. Cold exposure may assist immune system function, mitigating sleep inertia, and reducing muscle soreness. As with any intervention such as this, it is recommended that one makes an objective judgment based on the available scientific evidence to determine whether cold exposure is a valid and feasible practice for them.
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