Add two things to your health regimen that boost your immune system: 1) deliberate cold exposure, and 2) Vitamin D.
Everyone knows that winter is "flu season," and most people think it's because the outdoor temperatures get cold.
But cold temperatures are not directly responsible for the annual spate of infections. In fact, exposure to cold air is a huge boost to the immune system. For example, a study conducted by the US and Canadian Armies found that deliberate cold exposure can more than double the number of natural killer (NK) cells in the bloodstream. These are the white blood cell that respond to and destroy infection, including viruses, bacterial infections, and even cancer.
Given the beneficial effects of cold exposure on the immune system, what is the cause of "seasonal stimulus" (Cannel et al. 2006) in the rates of influenza infection?
According to Dr. John Campbell, a physician in the United Kingdom with a popular video log about coronavirus, the answer is Vitamin D deficiency.
Current dietary recommendations for Vitamin D were incorrectly established at levels just above those required to prevent rickets (Papadimitriou 2017), while increased levels of Vitamin D -- whether from increased sun exposure, a diet rich in wild fish, eggs, beef liver, and cheese, or from supplements--confers a myriad of benefits (Holick 2007) including:
reduced risk of infectious disease.
reversal of metabolic syndrome.
increased bone density,
prevention of Type 1 diabetes, and
protection against common cancers.
The evidence with regard to infectious disease is particularly strong, and timely (Adams & Hewison, 2008). For example, Figure 2 below shows how influenza infection rates in Norway compare with sun exposure for synthesis of Vitamin D (Juzeniene et al., 2010). The more sun, the less serious the flu.
Moreover, tropical latitudes do not show seasonality because they don't experience the same changes in levels of sunshine. Notice in Figure 3 below how the rates of influenza in the tropics stay mostly constant.
At Northern latitudes, when the sun is at its lowest angles in the sky and the days are shortest, the UVB solar radiation that reaches the surface of the Earth is insufficient to stimulate Vitamin D synthesis in the skin. Consequently, most people in the United States suffer from a Vitamin D deficiency in their bloodstream -- especially during winter months.
To make matters worse, the colder temperatures that prevail in winter cause people to cover more of their skin, and to stay indoors more often. In ancient times, our ancestors could still get an immune system boost from winter time cold exposure, but modern environments have created a comfortable existence away from the prophylactic powers of the natural environment by encouraging indoor habitation during winter -- the exact conditions under which the influenza virus can thrive.
Moreover, the immune function deficit that results from indoor comfort extends to all kinds of infections -- not just influenza. One of the great clinical advantages of cold and sun exposure is that they reduce the risk of all types of infections, including the secondary respiratory infections that accompany influenza infection, such as the pneumonia (Gruber-Bzura 2018).
Given the simplicity and affordability of Vitamin D supplements and deliberate cold exposure, there's no reason why you should have to experience a "flu season" at all. Once you understand the benefits, acting to keep yourself healthy is easy--although there are probably some people who are not yet convinced.
About the Author
Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.
For more information on taking charge of your own physical & mental health, visit the Self-Actual Engineering newsletter at https://seagertp.substack.com/.