The pineal gland produces and releases melatonin with a clear circadian (daily) rhythm, with the peak levels being observed at night. Upon production, melatonin is then secreted into the bloodstream as well as the fluid found around the brain and spinal cord (cerebrospinal fluid) and helps convey signals to the most distant of organs.
The circulatory system then carries melatonin from the brain to all the areas of the body. Tissues expressing proteins known as receptors specific for melatonin are capable of detecting the peak in circulating melatonin at night, which signals to the body that it’s night-time. The night-time melatonin levels are at least 10 times higher than the daytime concentrations.
Melatonin levels also have a circannual or seasonal rhythm, in addition to the circadian rhythm, with higher levels being observed in the autumn and winter, when the nights are generally longer, and lower levels are observed in the summer and spring.
Melatonin from the pineal gland is essential in many animals (including a wide range of birds and mammals) for regulating the body’s seasonal biology (e.g. behavior, reproduction, and coat growth) in response to the changing length of day. The importance of pineal melatonin in human biology isn’t clear, but it may help in synchronizing circadian rhythms in different parts of the body.
In humans, the nocturnal levels of melatonin usually decrease across puberty. The level of melatonin circulating in the body is detectable in samples of saliva and blood, and this is typically used for identifying internal circadian rhythms.
Much of the research into the functioning of the pineal gland involves the responses of the human brain to melatonin rhythms. According to the evidence, melatonin has 2 roles in humans: the involvement of the secretion of melatonin in initiating and maintaining sleep, and control by the day/night melatonin rhythm of the timing of other 24-hour rhythms.
Melatonin has, thus, usually been known as a ‘sleep hormone’, even though it is actually not essential for human sleep. Still, people tend to sleep better during the time when melatonin is secreted.
The association between pineal gland tumors and the timing of puberty suggests that melatonin could also have a minor role in reproductive development, but the mechanism of this action isn’t certain.
The secretion of melatonin by the human pineal gland varies markedly depending on age. It starts during the 3rd or 4th months of life and coincides with the consolidation of night-time sleep. Nocturnal melatonin levels peak at ages 1 to 3 years, following a rapid increase in secretion.
The nocturnal melatonin levels then decline slightly to a plateau that persists through early adulthood. Most people then experience a steady decline to an extent where the night-time melatonin levels in a 70-year old are only a quarter or less of those seen in young adults.
The secretion of melatonin during night-time melatonin is suppressed by a relatively dim light when the pupils are dilated. It has been suggested that this is the main way through which the prolonged use of devices such as smartphones and laptops before bedtime can have a negative impact on the secretion of melatonin, sleep, and circadian rhythms.
Besides its production in the body, melatonin can also be taken in capsule form. Clinical applications of melatonin include treating age-related insomnia, shift work, and jet lag. When administered at the right time of day, it helps reset the circadian rhythms of the body. There are also foods that have melatonin in them.
The resetting effect of melatonin has been reported for a variety of dose strengths, including those equivalent to the concentration of melatonin that’s produced naturally by the pineal gland. Higher melatonin doses can reset circadian rhythms, lower core body temperature, and bring on sleepiness. Many people feel our Unwind melatonin gummies can help.
How Is Melatonin Controlled?
In both humans and other mammals, the ‘master’ circadian clock drives the daily rhythm of pineal melatonin production. The ‘clock’ is found in a region of the brain known as the suprachiasmatic nuclei that expresses a series of genes termed as clock genes that oscillate continuously throughout the fay. This is synchronized to the solar day through light input from the eyes.
Complex nervous system pathways link the suprachiasmatic nuclei link to the pineal gland, which passes through various areas of the brain, into the spinal cord, and then finally reaches the pineal gland.
During the day, melatonin production is stopped by the suprachiasmatic nuclei, which sends inhibitory messages to the pineal gland. The suprachiasmatic nuclei, however, tend to be less active during the night, and the inhibition exerted during the day is reduced, which results in melatonin production by the pineal gland.
Light plays a key role in regulating the production of melatonin by the pineal gland. First, it can rest the suprachiasmatic nuclei clock and, as a result, the timing of when melatonin is produced. Secondly, being exposed to light during the body’s biological night reduces the production and release of melatonin.