Recycling this piece from Nature Communications that was published a few years back. In my view it relates to a core component of Chinese medical philosophy, which is the belief that the human body is is a thermofluidic system with an internal flux that is in constant communication with the yang qi of the environment. Nánjīng 65 provides a synopsis of this circannual cycle, stating there that “Man’s yang qi appears and disappears in accordance with the four seasons. Hence in spring the qi is in the wells, in summer in the brooks, autumn in the streams, and winter in the confluences. For treatment, the holes are always selected in accordance with the four seasons”.
In the original article, which you can read here, researchers state that “periodic seasonal changes have influenced all life forms, as exemplified by seasonal physiology and behaviours across plant and animal species”. They go on to say that “various biological processes show seasonal variation in humans, including ones with important immunological roles, such as vitamin D metabolism”. To summarize, the study found that in the winter your blood becomes more viscous and contains a denser blend of immunoproteins, while in summer the blood moves to the periphery, becomes more watery, and likewise undergoes a shift in hormones and immune system dynamics.
This sounds curiously similar to a passage from Suwen Chapter 13 describing a yearly rhythmic fluctuation in blood quality and immunity (camp & guard qi): “when heaven is warm and when the sun is bright, the blood is rich in liquid and the guard qi is at the surface. When heaven is cold and the sun is hidden, the blood congeals and the guard qi is in the depth”.
I also like to emphasize this quote from the article: “Temperature also could be a factor. We can’t be sure what’s causing this, all we can say is humans have adapted to their environments, … (and) their gene expression to match that variation”. In other words, human health is tied to how the environment behaves (changes) under the arbitration of time. This provides an example of how even in Western medical science that immunity is both a matter of constituency and orderliness in that it must be specific to the periodicity of the environment.
Lastly, this idea of communication between environmental and internal circadian rhythms relates to research concerning heat sensation functions in the skin and tongue.TRPV1 is a heat sensing protein that doesn’t simply sense chemicals or temperature. It “acts like a tiny computer, collecting information about the environment to help protect us from further injury.” I believe this relevant in that it helps explain some of the chemistry and biology involved when we utilize moxibustion, which is the practice of burning a small amount of material on specific locations on the body. It’s purpose is in part to help adjust and govern the flow of heat qi in the body such as to be specific to the environmental dynamic.
Read more on TRPV1 here.