GSE
MEALTONIN - The Darkness Hormone - Body's Natural Sleep Aid
MELATONIN
synchronizes body tissues to the daily cycle of
light and
dark The primary physiological function of
MELATONIN , whose secretion adjusts to night length
(daily duration of high-level secretion is shorter during the summer, when the nights
are short, and longer during the winter, when the nights are long),
is to convey information concerning the daily cycle of light and darkness
to body physiology
The circadian
rhythms affected by MELATONIN
- are the sleep cycle, the light/dark cycle, the thermoregulatory
cycle, the reproductive cycle, gonadal development, and immune cell functioning.
Your master
biological clock controls your "built-in" (i.e. endogenous)
circadian (daily) rhythms -
E.g. this inner timekeeper (a group of cells, called the SCN, residing in your brain's
hypothalamus) tells you when it's time to wake up or go to sleep. Although
self-sustained, the endogenousrhythms can be adjusted (entrained) by environmental
factors, primarily by light and
dark .
(also forced activity and rest, feeding cues, knowledge of clock time,
MELATONIN and others);
Light
reaches your master biological clock (SCN) via your eye's
optic nerve, where it initiates events such as waking you up, and processes associated
with being awake .
The Biological Clock
MELATONIN
is produced/secreted under control of the master biological clock (in response
to darkness), such that MELATONIN
levels have a 24-hr cycle of marked circadian rhythmicity, which regulates
core body temperatures, adrenal CORTISOL
(stress hormone)
and more
The circadian
rhythm of MELATONIN inversely correlates with the temperature rhythm in humans
- MELATONIN levels in blood
increase as core body temperature decreases.
- Low circulating levels of
MELATONIN in the daytime
- Rising to maximal levels of
MELATONIN during the night
MELATONIN
feeds back to the "Biological clock"to regulate its activity - most of the brain receptors for
MELATONIN
are located in the SCN (in mammals)
Circadian
desynchrony (with its attendant sleep problems)
is directly related to the degree of light perception - many
blind people with no conscious or unconscious light perception MELATONIN and other circadian rhythms.
MELATONIN
supplementation can produce shifts in circadian rhythms in a number of species -
including rats, sheep, lizards, birds, and humans MELATONIN
is given in the absence of light input. Thus,
for example, giving MELATONIN
to blind people can help set their biological clocks.
MELATONIN appears
to have an inhibitory affect on the reproductive rhythm
- In humans,
MELATONIN secretion is inversely correlated
with gonadal development -
peak MELATONIN
levels fall just prior to the onset of puberty; also, higher levels of plasma
MELATONIN have been noted in women
with amenorrhea (no menstruation).
- In mammals
other than humans, MELATONIN
possibly acts as a breeding and mating cue
- since it is
produced in greater amounts in response to the longer nights of winter and less
so during summer. Dr. George Brainard found that the gonads of male hamsters
increased and decreased in size depending on the breeding season or season. He could
change their gonad size and MELATONIN
production by altering their exposure to light/dark cycles. Animals
who time their mating or breeding to coincide with favorable seasons (such as spring)
may depend on MELATONIN production
and the biological clock to regulate their reproductive cycles
