970x125
As fall begins, the days become shorter, and the nights longer, especially at higher latitudes. Fall changes our routines. People tend to return home earlier, resulting in fewer people on the streets. In many cities, evening traffic starts earlier, and the streets become empty at night. The start of school and universities in the fall causes much of the young population, who typically spend time outdoors, to leave the streets and recreational areas. Instead, spending time at home, attending parties with friends and family, and visiting pubs and coffee shops have become popular activities. However, this shift from summer to fall habits varies depending on culture and geographical location. It appears that reading books, playing video games, and watching films and series have also become more popular.
In addition to daily changes by the beginning of fall, some bodily alterations may occur. These behaviors are linked to how reduced daylight can affect people’s perception of available time, mood, sleep, and daily routines. Darkness causes winding down, rest, and indoor activities. People often feel as if they are “running out of light,” which leads them to adjust their schedules to reduce evening outdoor and social activities.
Your Body’s Internal Clock: Winding Down for Winter
Human biological rhythm is known as circadian rhythms. This biological clock has evolved to adapt to day-night cycles based on light and temperature and influences bodily systems, including hormone release, body temperature control, and metabolism regulation, impacting overall health. The suprachiasmatic nucleus (SCN) in the hypothalamus acts as the main part of the circadian clock. SCN receives the visual signals directly from the eyes via the retinohypothalamic tract. It regulates the pineal gland’s production of melatonin. This hormone rises during darkness and drops by daylight. An increase in melatonin induces sleep. Body temperature is also controlled by dark-light rhythm, typically decreasing slightly at night to facilitate sleep [1].
It appears that the seasonal changes at the beginning of fall have an evolutionary origin. As the days grew shorter, our cave-dwelling ancestors sought shelter and ended their outdoor activities earlier. Thus, returning home earlier in the fall may partly result from evolutionary adaptations to changes in environmental light. They spent more time beside the fire, engaging in storytelling and painting on the cave walls. The leisure from summer duties, such as hunting and gathering food for winter, provided an opportunity to extend social bonds.
Seasonal Affective Disorder (SAD)
SAD is a kind of depression associated with seasonal changes and typically starts in the fall, may continue during the winter months. Signs of SAD include feelings of sadness, hopelessness, having low energy, and changes in sleep and appetite. SAD is more prevalent in countries located at northern latitudes, including Canada and Scandinavian countries. It is often treated with psychotherapy, antidepressant drugs, and light therapy. In some northern countries, it is common to use artificial table lamps at home or in the office to compensate for the lack of sunlight and to prevent SAD [2].
The Risk of Depression at the Onset of Fall and Vitamin D Deficiency
Vitamin D deficiency is one of the most common nutritional deficiencies in the world. Its level in the body is dependent on sunlight exposure, dietary factors, and certain diseases. This vitamin in the body acts as a gene expression factor that regulates a wide range of gene expression. The genes influenced by vitamin D play roles in various physiological processes, including metabolism, immune system function, cell division, cancer development, and the absorption of calcium and phosphate from the gastrointestinal tract.
Vitamin D supports the immune response to infections, and its deficiency is associated with an increased susceptibility to the common cold and flu, particularly during fall and winter. It also plays a critical role in metabolic regulation by improving the body’s sensitivity to the key metabolic hormone, insulin. Consequently, vitamin D deficiency may exacerbate health outcomes for individuals with obesity or diabetes.
The Role of the Sunshine Vitamin in SAD
Sunlight is the primary catalyst for vitamin D synthesis in the skin. Reduced sunlight exposure and less time spent outdoors during fall and winter frequently lead to a high prevalence of vitamin D deficiency. This is especially common in regions experiencing prolonged winters, shorter daylight hours, and high seasonal rainfall.
Vitamin D plays a significant role in the relationship between seasonal changes in sunlight and depression, particularly in seasonal affective disorder (SAD). Vitamin D acts not only as a nutrient but also like a neurosteroid. It affects the central nervous system by influencing neurotransmitters and neuroinflammation. Serotonin, norepinephrine, and dopamine are major neurotransmitters in the control of mood stability. Empirical evidence indicates that both vitamin D supplementation and light therapy can alleviate mood disturbances in individuals with SAD, though treatment efficacy varies. Sunlight exposure is thought to improve mood through multiple pathways [3]. In addition to stimulating vitamin D synthesis, it may directly influence neurobiology by reducing cortisol levels and enhancing other brain functions, thereby helping to mitigate depressive symptoms. Outdoor light exposure is strongly correlated with improved mood and lower depression risk. Sunlight promotes vitamin D synthesis and lowers stress-related hormones such as cortisol, further contributing to mental well-being [4].
Depression Essential Reads
In summary, substantial evidence supports the link between vitamin D, sunlight exposure, and depressive symptoms. This connection is particularly evident in cases where seasonal reductions in sunlight lead to vitamin D deficiency, a condition that can subsequently contribute to the development of depressive states and Seasonal Affective Disorder (SAD). For individuals affected during low-sunlight periods, both vitamin D supplementation and light therapy represent viable therapeutic strategies to alleviate these symptoms [5].
