Boosting Immunity through Diet and Lifestyle

Several studies have demonstrated that cold temperatures 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.

But couldn't something like vitamin D exposure better explain these 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 the sunshine vitamin, 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.

That seems a bit of a stretch.

But then this study was published.

Standard housing temperatures for laboratory mice in research facilities is mandated to be between 20 and 26 Celsius, like typical room temperatures in the 70s Fahrenheit.

But that's chilly for mice, causing chronic mild cold stress.

When that stress is alleviated by housing at warmer temperatures, like in the 80s Fahrenheit, researchers observed a striking reduction in tumor formation, cancer growth rate, and metastasis.

Warmer was better.

They suggested that the cold stress results in a suppression of anti-tumor 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, at least through 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 it instead be hormesis, that which doesn't kill us makes 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.

[laughs] 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, quote, unquote, "treating the insane," and then used as an instrument of 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.