Have you ever heard of the term immune clock? From a modern medical perspective, the philosophy from Donguibogam that our body must adapt to the movements and transformations of heaven and earth qi is deeply related to the fact that our biological clock and neuro-endocrine-immune network are exquisitely regulated in response to seasonal changes. It is not just about the seasons shifting; changes in sunlight exposure, temperature, humidity, and even diet brought by seasonal shifts all have complex effects on our body's immune system.
The hypothalamus within our brain functions like the command center regulating all biological functions in our body. It detects changes in the length of day and night—meaning changes in sunlight exposure—and regulates the secretion of hormones like melatonin and cortisol. For instance, as daylight shortens in autumn and winter, melatonin secretion increases, affecting sleep quality, while the synthesis of serotonin, the happiness hormone, decreases, leading to more people experiencing seasonal affective disorder. These hormonal changes directly affect the activity of immune cells in our body. Although cortisol is known as a stress hormone, it actually plays an important role in regulating immune responses. However, if cortisol secretion is disrupted by chronic stress or irregular routines, immune cell function deteriorates, leaving one vulnerable to infection.
Furthermore, modern research demonstrates that the activity of immune cells themselves varies according to the season. The number of specific immune cells or the production of cytokines fluctuates by season, and studies even show that the effectiveness of the influenza vaccine varies depending on the season. This serves as evidence that our bodies have evolved in response to patterns of seasonal infectious diseases passed down from the past. Particularly during the change of seasons, rapid temperature fluctuations and dry environments weaken the respiratory mucosa, making viral invasion easier. Moreover, when the body consumes a large amount of energy trying to adapt to sudden temperature shifts, resources allocated to the immune system naturally decrease, which can cause a temporary drop in immunity.
Vitamin D also plays an important role. During autumn and winter when sunlight exposure decreases, synthesizing vitamin D becomes difficult, yet vitamin D is an essential nutrient for the maturation and activation of immune cells. When vitamin D is deficient, the immune response weakens, potentially increasing the risk of contracting a cold or influenza. Gut health cannot be overlooked either. Did you know that more than 70% of our body's immune cells reside in the gut? When diets change or stress rises with the change of seasons, shifts occur within the gut microbiota ecosystem, which can promptly lead to decreased immunity.
Ultimately, the movements and transformations of heaven and earth qi described in Donguibogam can be seen as an insightful explanation of how sensitively our body's complex neuro-endocrine-immune network reacts to and is regulated by the external environment, especially seasonal changes. We must not forget that while our body has a remarkable ability to protect itself, it can falter at any time without delicate attention and care toward changing nature.
