This is an exclusive excerpt from my book, The Physiology of Yoga.
If you have spent time in a part of the world with cooler climate you have surely all been warned, “Don’t forget your coat or you’ll catch a cold!” Does exposure to cold temperatures somehow weaken our immune systems and make us more susceptible to getting ill?
A review of the research studies on this topic by Castellani, Brenner, and Rhind (2003) concluded that moderate cold exposure has no detrimental effect on the human immune system. It is suggested that colds and flus are more prevalent in the winter because people spend more time indoors, in closer contact with other people who can pass on their germs, and viruses like influenza stay airborne longer when air is cold and less humid.
A report by Xu and colleagues (2020) looking at COVID-19 transmission suggested that warmer temperature and moderate outdoor ultraviolet exposure may offer a modest reduction in transmission. Furthermore, cold exposure training can be beneficial to building adaptations that improve our tolerance to cold environments, a technique that climbers commonly use before venturing up a mountain. So, when you are out in cold weather, stay wrapped up for your comfort, but let go of the idea that by doing so you are somehow protecting your immune system.
There is also preliminary evidence that acclimating to cold conditions lowers sympathetic activation and causes a shift toward increased parasympathetic activity (Mäkinen et al. 2008). This could be explored by regularly having cold showers. Exposing one’s body to cold temperatures is one of the three pillars of the increasing popular Wim Hof Method. A systematic review by Knechtle et al (2020) reported that regular swimming training in cold water seems to have a positive effect on various systems such as the cardiovascular system, endocrine system, immune system and the psyche. However, cold water swimming still poses a significant health risk for inexperienced and untrained swimmers.
Will cold yoga be the next trend? ;-)
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References:
Castellani, J., Brenner, I., and Rhind, S. 2003. “Cold Exposure: Human Immune Responses and Intracellular Cytokine Expression.” Medicine and Science in Sports and Exercise 34:2013-2020.
Knechtle, B., Waśkiewicz, Z., Sousa, C., Hill, L., and Nikolaidis, P. 2020. “Cold Water Swimming—Benefits and Risks: A Narrative Review.” International Journal of Environmental Research and Public Health 17(23): 8984.
Mäkinen, T., M. Mäntysaari, T. Pääkkönen, J. Jokelainen, L. Palinkas, J. Hassi, J. Leppäluoto, K. Tahvanainen, and H. Rintamäki. 2008. “Autonomic Nervous Function During Whole-Body Cold Exposure Before and After Cold Acclimation.” Aviation, Space, and Environmental Medicine 79 (9): 875-882.
Xu, R., H. Rahmandad, M. Gupta, C. Digennaro, N. Ghaffarzadegan, H. Amini, and S. Jalali. 2020. “The Modest Impact of Weather and Air Pollution on COVID-19 Transmission.”