Melatonin is a natural hormone
made by your body's pineal gland - a pea-sized gland located just
above the middle of the brain. During the day the pineal is inactive.
When the sun goes down and darkness occurs, the pineal is "turned
on" and begins to actively produce melatonin, which is released
into the blood. Usually, this occurs around 9 p.m. As a result,
melatonin levels in the blood rise sharply and you begin to feel
less alert. Sleep becomes more inviting. Melatonin levels in the
blood stay elevated for about 12 hours - all through the night -
before the light of a new day when they fall back to low daytime
levels by about 9 a.m. Daytime levels of melatonin are barely detectable.
Besides adjusting the timing of the clock, bright light has another
effect. It directly inhibits the release of melatonin. That is why
melatonin is sometimes called the "Dracula of hormones"
- it only comes out in the dark. Even if the pineal gland is switched
"on" by the clock, it will not produce melatonin unless
the person is in a dimly lit environment. In addition to sunlight,
artificial indoor lighting can be bright enough to prevent the release
of melatonin.
The amount of melatonin released at night varies among individuals,
but it is somewhat related to age. Children on average secrete more
melatonin than adults, which decreases further with age. However,
research has shown that older people with sleep problems do not
always have lower melatonin levels than people who experience normal
sleep.
The pattern of waking during the
day when it is light and sleeping at night when it is dark is a
natural part of human life. Only recently have scientists begun
to understand the alternating cycle of sleep and waking, and how
it is related to daylight and darkness.
A key factor in how human sleep is regulated is exposure to light
or to darkness. Exposure to light stimulates a nerve pathway from
the retina in the eye to an area in the brain called the hypothalamus.
There, a special center called the supra-chiasmatic nucleus initiates
signals to other parts of the brain that control hormones, body
temperature and other functions that play a role in making us feel
sleepy or wide awake.
The SCN works like a clock that sets off a regulated pattern of
activities that affect the entire body. Once exposed to the first
light each day, the clock in the SCN begins performing functions
like raising body temperature and releasing stimulating hormones
like cortisol. The SCN also delays the release of other hormones
like melatonin, which is associated with sleep onset, until many
hours later when darkness arrives.
Melatonin is the major neuroendocrine modulator of circadian bio-rhythms.
The ebb and flow rhythm of melatonin is synchronized with light-dark
cycles and is strongly affected by day length, artificial light,
electromagnetic energy, exercise and other factors. Melatonin not
only has a pivotal role in regulating the sleep-wake cycle, but
also has a far-reaching biological influence over many functions
in your body.
When levels of melatonin are too low or there is inadequate melatonin
throughout the night, sleep can become a challenge.
Some of the causes of low melatonin include:
Excess exposure to light during evening hours.
Mother Nature brings dusk for a reason!
Use of certain prescription and over-the-counter
medications such as ibuprofen, aspirin and other NSAIDs, anti-anxiety
and anti-depressants, blood pressure medications and steroids
such as prednisone.
Evening exercise, which decreases melatonin
up to 3 hours post-workout.
Excess intake of vitamin B12 (doses
over 3,000 mcg may inhibit melatonin production).
Some studies show promise for the use of
melatonin in shortening the time it takes to fall asleep and reducing
the number of awakenings.
Melatonin might help shift workers on irregular shifts who need
to adjust their schedules. When taken in low doses at the appropriate
time, melatonin can help advance or delay the sleep-wake cycle.
The effect can last for six hours.
