When light enters your eyes, it not only goes to your visual centers enabling you to see; it also goes to your brain’s hypothalamus.
Hypothalamus: the Brain’s Brain
The hypothalamus is a fundamental part of the brain that projects downward ending in the pituitary gland. The hypothalamus regulates homeostasis. It regulates thirst, hunger, weight regulation, body temperature, water balance, the sleep/wake cycle & blood pressure. It also initiates the body’s stress response, affects our emotions, and controls our immune functions.
The hypothalamus is so important to the body’s functioning that it is known as the “brain’s brain”. This means that it controls the part of the nervous system regulating automatic and metabolic processes in the body.
Pituitary: the Body’s Master Gland
The pituitary gland is about the size of a pea and secretes essential hormones to regulate homeostasis. It is functionally connected to the hypothalamus & is considered to be the “master gland”.
Hormones secreted from the pituitary help with growth, uterine contractions, blood pressure, breast milk production, thyroid gland function, turning food into energy, etc.
Our Body Clock
Our “body clock”, is also housed in the hypothalamus. Our body clock is controlled by circadian rhythms, which are the 24-hour cycles of light and darkness. These light-sensitive rhythms are not an invention of modern times, they are biologically imposed by Mother Nature. Consequently, anything that disrupts these rhythms (like inadequate sunlight) has a far-reaching impact on our body’s ability to function.
This explains why, since sunlight has been shown to be the most effective regulator of the body clock, it is also the quickest method of recovering from jet lag. (Or you can supplement sunlight with full spectrum lighting indoors.)
But it gets even more interesting! In 1998, scientists found that they could reset the body clock of study subjects by shining bright lights onto the back of their knees. This demonstrates that areas of the skin are significantly affected by light, just like the retinas of our eyes. This led researchers to conclude that the body may have more than one body clock, although the eyes still seem to be the main route by which the circadian system senses light.
Our Body’s Light Meter
The body clock control centers in the hypothalamus are also connected to the pineal gland, which is considered the body’s “light meter”. The pineal gland secretes the important hormone melatonin. It is a small endocrine gland in the brain that produces melatonin, a hormone that affects wake/sleep patterns. The pineal gland got its name because it is shaped like a tiny pinecone.
Melatonin: The Hibernation Hormone
Melatonin, the “hibernation hormone”, increases with decreased light, which explains that tired feeling that comes on when it begins to get dark outside, even if it is only 4 o’clock in the afternoon! And, it also explains why decreased melatonin is found in those with insomnia (and why full spectrum light is beneficial for healthy sleep).
Serotonin: The Mood Elevator
Conversely, serotonin, the brain hormone associated with mood elevation, rises with exposure to bright light, and falls with decreased sun exposure. This has been proven by many scientific studies, including one reported in the well-respected medical journal Lancet in 2002. This study measured blood levels of serotonin, finding that production of serotonin by the brain was directly related to the duration of bright sunlight.