Why do we get depressed in winter? We look at the effects of seasonal changes on our bodies and minds, and the science behind them.
As the hot summer sun sets and fall slowly approaches, more people than ever are complaining of depression. This is a serious problem that cannot be dismissed as a simple change in mood, and it is gaining more attention as interest in mental health grows in modern society. In particular, many literary works and popular songs set in autumn and winter evoke a lonely atmosphere by reflecting the images of fallen leaves and cold winds, highlighting the impact of these seasonal changes on people’s emotions. Of course, many people experience fall and winter as the seasons of loneliness.
Some people experience severe depression continuously as the seasons change, and their condition is classified as “seasonal affective disorder. It is characterized by symptoms such as persistent depression, decreased activity, hypersomnia, decreased sex drive, increased appetite, and weight gain. It is unique in that approximately 83% of patients are women. Meanwhile, in 1991, it was estimated that the population suffering from seasonal affective disorder in Siberia and Alaska in Russia was about 16.2% of the total population, and in 2004, about 5% of the total population in Australia. With 35% of people suffering from this disorder, it is clear that seasonal depression is a condition that has affected the mental health of people around the world, rather than just a type of emotion experienced by a small number of people.
But is seasonal affective disorder simply a product of the dreary visual and tactile images of the cold season? Unfortunately, not much is known about the direct causes and scientific mechanisms of seasonal affective disorder. However, in recent years, scientists have been adding evidence that seasonal depression is a disease caused by the regulation of the body’s secretion of serotonin and melatonin.
First, let’s look at the relationship between seasonal changes and hormone secretion, and the possible effects of serotonin and melatonin on depression. First, seasonal changes are related to changes in the amount of solar energy received by the earth’s surface. Seasons are the sum of general weather phenomena that change according to the amount of sunlight each point on the Earth receives as the Earth revolves around the Sun. In addition to the phenomenon of revolution, the rotation of the Earth, which is tilted by about 66.5° along the central axis relative to the plane of revolution, further solidifies the change of seasons. Based on the Earth’s one-year rotation cycle, regions in the northern and southern hemispheres experience different solar noon altitudes and lengths of daylight at different times of the year. The higher the altitude at which the sun is at its highest point in the sky, the more sunlight energy that point receives, with summer being the season when the amount is at its highest and winter being the season when it is at its lowest.
Melatonin, on the other hand, is a hormone produced by the pineal gland, an endocrine gland in the hypothalamus, that helps the body adapt flexibly to day and night. Melatonin plays a particularly complex role in regulating the body’s visual system. For example, melatonin regulates the degree of sensitivity to light in the melanocytes of the skin and retina. The method of regulation is simple: by increasing or decreasing the amount of melatonin produced over time, other effects are also increased or decreased. Here, melatonin is mainly produced in the body based on the biological cycle, which is a naturally occurring cycle. This is due to the fact that one of the processes of melatonin production, N-acetylation, is dependent on the biological cycle. N-acetylation is a reaction in which a hydrogen atom is replaced by an acetyl group (CH3CO-) in an organic compound with an amino group (-NH2). Melatonin is made from serotonin, another hormone produced in the pineal gland, through two processing steps, N-acetylation and O-methylation. Since N-acetylation is a reaction that is most active at night, melatonin is also produced at night.
The standard for night varies depending on the season. Our body senses the amount of light, which changes over time, and regulates its biological cycle. Therefore, even if it is the same time, if our body is exposed to more light than before, the production of melatonin is inhibited. The average starting point (DLMO) of melatonin secretion is 9 pm, but in fall and winter the starting point is earlier and the end point is later, increasing the total amount of secretion. Serotonin, on the other hand, is produced in response to light, unlike melatonin. Therefore, the total amount of serotonin secreted decreases in the fall and winter as the days get shorter.
So what is the relationship between the secretion of serotonin and melatonin, which change according to the season? Serotonin is a type of neurotransmitter, and a decrease in serotonin causes a decrease in the ability to transmit neurotransmitters in some way. The exact mechanism for this has not been identified, but doctors have found through analysis of numerous patients and trial and error in treatment that a decrease in serotonin is associated with depression, decreased sociality, and decreased appetite. Melatonin, on the other hand, is a hormone that induces sleep and lowers body temperature. In fall and winter, serotonin activity decreases and melatonin activity increases, which means that people generally feel emotionally down, while their sleep time increases and their physical activity decreases. Of course, the direct cause of the effects of serotonin and melatonin on depression has not yet been identified. However, if seasonal changes are applied to this, we can speculate that these hormones are somehow related to this disease.
With the development of modern science, the causes and treatments for many physical ailments have been identified. However, the scientific causes of mental illness remain in many ways a mystery, apart from empirical facts. Is science the only clue to the mystery of the human mind? If so, is our mind controlled by the body and the environment? It is not known when we will be able to answer these age-old questions. But for now, at least for the condition of seasonal affective disorder, we have learned, on the basis of science and experience, that there is a single link, hormones. I hope that more links will be found and that many people will be relieved of the emotional pain that comes with the cold season.
