Melatonin
Melatonin is produced by the pineal gland. Scientists believe that the pineal gland and melatonin are the body's primary timekeepers—its clock and calendar—providing information about the time of day, the season of the year, and the phase of life to the brain and throughout the body. Melatonin is thought to influence internal processes to ensure that all of the body's systems work harmoniously. Any disruption in this internal organization can make the body more vulnerable to diseases.
Melatonin is produced almost exclusively at night or in a light-free environment. (It's even nicknamed "the chemical expression of darkness" by scientists due to its nocturnal behavior.) Melatonin levels in the blood are up to ten times higher at night than during the day. This significant nocturnal production of melatonin signals to the rest of the body that it's time to sleep. Melatonin supplements have been used for many years to address sleep-related issues, such as insomnia, sleep apnea, and jet lag.
In the morning, when the presence of light is detected, melatonin secretion ceases, kickstarting the production of other hormones and initiating various bodily activities. This orderly daily rhythm is of utmost importance for our physical well-being, cognitive abilities, and emotional health.
Animals adapt their behaviors, including reproduction, hibernation, and migration, based on the changing seasons. It's believed that these animals perceive seasonal variations through the patterns of light and darkness. The secretion of melatonin is the mechanism responsible for implementing these behavioral changes. As daylight hours decrease in the autumn, animals' melatonin production automatically increases, facilitating the extended sleep characteristic of hibernation. When daylight hours extend during the spring, the pineal gland secretes less melatonin, signaling a shift in physical activity patterns.
The ways in which these seasonal patterns impact human behavior are currently under intense investigation. Some researchers posit that seasonal melatonin levels may offer insight into Seasonal Affective Disorder.
Chronobiology is a burgeoning science focused on identifying our natural cycles and internal clocks and understanding how they interrelate. It examines natural rhythms like temperature fluctuations, weather patterns, and light-dark cycles to comprehend their effects on the life cycles of both men and women.
Melatonin and Serotonin
Melatonin influences the production and action of several other hormones in the body. It works in concert with serotonin, a potent neurotransmitter derived from it. Serotonin plays a pivotal role in various central physiological processes, encompassing pain perception, temperature regulation, and blood pressure control, as well as various neuropsychological functions like appetite, memory, and mood. Similar to melatonin, serotonin's levels influence a multitude of endocrine functions, including those managed by the hypothalamus and pituitary gland.
Generally, melatonin and serotonin aren't simultaneously active in the body. As mentioned earlier, melatonin is active at night, while serotonin predominates during the day. While both tend to modulate endocrine functions, excessively high serotonin levels in the bloodstream can have adverse effects on the cardiovascular system, such as blood clotting and constriction of blood vessels, among other issues. Unlike melatonin, serotonin levels do not diminish with age; they increase in relation to other hormones and neurotransmitters. Experts specializing in the study of aging and the elderly believe that this age-related imbalance between serotonin and melatonin may play as significant a role in the aging process as the deficiency of melatonin, particularly in relation to heart disease. In the absence of melatonin's free-radical scavenging during the night, more harm might occur to blood vessels, prompting the release of additional serotonin.
Research has also revealed that individuals experiencing severe depression often have low levels of serotonin, as well as dopamine and norepinephrine—three neurotransmitters used by the brain. Hence, the connection between serotonin and melatonin, along with their reliance on the body's internal clock, could elucidate the depression experienced by those with Seasonal Affective Disorder (SAD).