The period of storing and sealing described in Donguibogam is very closely linked in modern medicine to seasonal affective disorder or winter lethargy. One of the main culprits of winter fatigue is a lack of sunlight. When sunlight decreases, changes occur in the function of the hypothalamus in the brain; in particular, the balance of melatonin and serotonin, hormones that play vital roles in regulating sleep and mood, is easily disrupted.
Sunlight suppresses melatonin secretion and promotes serotonin secretion. However, when winter arrives and sunlight exposure decreases, melatonin secretion rises excessively even during the day, making one prone to excessive sleepiness and lethargy. Conversely, as the production of serotonin, known as the happiness hormone, declines due to reduced sunlight, it can lead to low mood, depression, impaired concentration, and increased appetite. In particular, cravings for carbohydrates often intensify. While this is an instinctive response by the body to replenish energy, it easily leads to unhealthy eating habits.
Furthermore, sunlight is essential for synthesizing vitamin D, and vitamin D deficiency is common during winter. Vitamin D broadly affects overall health beyond just bone health, including immune function, hormone regulation, and neurotransmitter synthesis. A lack of vitamin D can cause chronic fatigue, muscle pain, decreased immunity, and even feelings of depression. The wisdom of our ancestors, who told us to wait for the sunlight in winter, is thus validated by modern science.
Irregular modern lifestyle habits are also problematic. The habit of looking at smartphone or computer screens late into the night interferes with melatonin secretion and degrades sleep quality, fueling a vicious cycle that leads back to chronic fatigue and lethargy. Our bodies possess a circadian rhythm, a biological clock operating on roughly a 24-hour cycle. When this rhythm is broken, all bodily functions, including digestion, immunity, and hormonal balance, can become disrupted. Maintaining this rhythm is even more critical during winter.
Ultimately, winter chronic fatigue is not simple laziness. It is a natural bodily response and warning sign resulting from a complex interplay of neurotransmitter imbalances caused by lack of sunlight, vitamin D deficiency, and a disrupted biological rhythm. It is important not to ignore the small signals our bodies send us, but to tend to them with care.
