Can Cold Showers Improve Immune Function?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Several studies have demonstrated that cold temperature may be a potential risk factor for cancer development. For example, this study compared the 50 countries with the highest cancer rates to the countries with the lowest cancer rates and concluded that people living in cold environments may have a higher risk of getting and dying from cancer. A similar study within the United States found that colder counties were associated with a greater cancer incidence among American women. But couldn’t something like vitamin D exposure better explain these kinds of findings? Patients diagnosed with cancer during summer months may have a better prognosis than those diagnosed during the winter. But again, this could be because of vitamin D. Evidently, an animal colony had less cancer when they moved from a colder country to a warmer country, based on some observation published in 1939. Seems like a bit of a stretch, but then this study was published.

Standard housing temperature for laboratory mice in research facilities is mandated to be between 20 to 26 degrees Celsius, like typical room temperature in the 70s Fahrenheit. But, that’s chilly for mice, causing mild chronic cold stress. When that stress is alleviated by housing at warmer temperatures, like in the 80s Fahrenheit (27––32 °C), researchers observed a striking reduction in tumor formation, cancer growth rate, and metastasis. Warmer was better. They suggest that the cold stress results in a suppression of antitumor immunity. Then why do they keep mice at that lower temperature? It reduces the frequency of cage cleaning, and helps ensure the thermal comfort of the staff.

The proposed mechanism is the activation of the fight-or-flight response that leads to the release of the stress hormone norepinephrine, also known as noradrenaline. Take a dip in a typical cold plunge, and there can be a doubling of norepinephrine levels in the blood within minutes. And we don’t seem to habituate, meaning we get that same bump in norepinephrine after each cold-water immersion, even after three months of regular plunges. Might that be suppressing immune function? Or might that be hormesis—that which doesn’t kill us make us stronger?

Cold-water swimmers claim to suffer fewer and milder infections as a result of the practice. Even if that’s true, cold-water swimmers are, swimming—maybe it’s the exercise, not the cold? How would we figure this out? To control for any effect of swimming, researchers compared cold-water swimmers to indoor heated-pool swimmers, and found no difference in upper respiratory tract susceptibility between swimmers in cold water and heated pools. Therefore, cold water swimming appears to have no protective effect.

What about regularly taking cold showers? Cold showers were first designed for the purpose of treating the insane, and then used as an instrument in torture in prisons before it started killing too many people. Rather than being abandoned, however, the shower was transformed by the use of warm water to actually clean people. I had no idea.

If you randomize people to short daily cold showers versus hot showers for a few months, regular cold shower exposure does appear to put the immune system on high alert. Does that actually translate into less sickness? There’s only been this one randomized trial on the effect of cold showering on health and work: a randomized, controlled trial. Participants were randomized to shower as normal but end their showers with 0, 30, 60, or 90 seconds of cold water.

And compared to the no-cold group, the different cold-water groups collectively had a 29% reduction of self-reported sick leave from work, but no fewer self-reported days of illness. So, maybe the cold showering made them less sick, even if they were sick for the same duration? The problem, of course, is that while there was a control group, there was no placebo control. So, maybe the cold-showering groups chose to skip work less for some other reason. It’s not clear, but at least it didn’t seem to show cold showering was harmful to immune function in the short-run in healthy adults.

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Motion graphics by Avo Media

• cancer
• exercise
• vitamin D