The pineal gland—a tiny organ weighing about one gram and located in the center of the brain—is responsible for regulating the cycle of sleep and wakefulness in the human body. Despite its small size, the pineal gland plays a huge role in the body, regulating many of its vital functions.
For example, in daylight, it produces serotonin—a substance known as the “pleasure hormone” or the “happiness hormone.” When serotonin levels are sufficient, we’re in a good mood and find joy in life. But if there isn’t enough, we experience apathy, despondency, and low spirits, depression, or, conversely, increased aggression, irritability, anxiety, and restlessness.
But when it gets dark outside, the pineal gland begins to produce another hormone—melatonin—which is responsible for healthy, restful sleep. Darkness (preferably complete) and nighttime are the two most important conditions for normal sleep. Produced only during the dark hours of the day, melatonin not only has a sleep-inducing effect but also promotes the body’s recovery: it restores the nervous, immune, and cardiovascular systems to normal function.