Melatonin is a human hormone secreted in the pineal gland, located right in the center
of the human brain. The purpose of melatonin is to regulate the circadian rhythms…in
simple terms melatonin decides when it's time to sleep! Not surprisingly, melatonin's
secretion in the blood stream depends on daylight cycles. During dark hours higher
concentrations of melatonin are produced, while during the day its concentration
The process of sleep cycle synchronization all starts from our eyes! Certain photosensitive
ganglions in the retina (not involved in image recognition), "measure" the ambient
level of light and respond activating the photopigment melanopsin. This so called
non-image-forming light response has several final effects including: regulating
the pupil size in response to light, and affecting melatonin production. The latter
synchronizes of the sleep cycles with the daylight changes. An interesting feature
of the circadian cycle is its ability to operate without external stimuli. In simple
words, our brain is virtually capable of deciding when it's the right time to sleep
regardless of external inputs.
To be beneficial for the organism however, this internal clock need to be synchronized
with the external time. The dependence of melatonin production on the daylight cycle
is exactly part of this synchronization process.
In addition to naturally regulating sleeping patterns, melatonin is also one of the
most powerful antioxidants. To understand how melatonin exerts its antioxidant activity,
let's take a step back and see in general how antioxidants work. During the normal
course of biochemical reactions in living organisms, several chemical substances
(such as free radicals) can be generated, capable of damaging DNA, induce cancer,
Alzheimer, Parkinson disease, and heart conditions. Natural antioxidants, in the
body, have the ability to react with these substances and neutralize their detrimental
activity. Most of these compounds however tend to lose their protective antioxidant
skills after they react with radicals and eventually are transformed themselves into
Melatonin acts in a different way. Upon reacting with oxidant species, melatonin
permanently binds free radicals forming stable products that do not have pro-oxidative
properties. These reaction products have themselves antioxidant properties thus extending
the protective activity of melatonin beyond its first reaction step. In addition
to that, melatonin is capable of crossing cell membranes and the brain barrier, which
are usually impermeable to other molecules, bringing its protective activity of melatonin
to every compartments of the body.
Before you start filling your bathroom cabinet with melatonin and antioxidant supplements
keep in mind that the research on antioxidants and their role in preventing diseases
is very controversial. It is not clear yet if antioxidants have a real role in preventing
oxidative stress and the diseases associated with it.
Because of its properties, melatonin was for some time considered a miracle molecule.
Particularly during the early 90's, melatonin was included in "longevity" products,
and received a lot of space in the press. Nowadays, the physiological properties
of melatonin are better documented. Because of its ability to induce a "natural"
sleep melatonin is a very popular supplement to attenuate jetlag and fight insomnia,
and it is now the standard treatment for certain sleeps disorders.
In food, melatonin is found in yeast, rice, and vegetable products. Interestingly,
melatonin from food can not only affect melatonin blood concentration through ingestion,
but also trough interaction with other nutrients. Tryptophan for example, a nutrient
associated with post-meal drowsiness, was suggested to affect melatonin production
in the gastrointestinal tract.
Melatonin is in general considered safe. Dosages in the hundreds of milligrams were
administered to rats without adverse effects. However, although commercial supplements
containing melatonin are available over the counter in the US, melatonin is still
banned from sale without prescription in several countries including Germany.
Although its supplementation is considered safe, melatonin has been associated with
unwanted side effects. High doses of this hormone (3mg per day and above) have been
reported to induce drowsiness, headaches, next-day irritability, nausea and vivid
dreams. As far as the recommended dosage of melatonin, common commercial products
on the market come in pills of 1mg, 3mg and 5mg, and its effect varies depending
on the individual. Since the human brain naturally produces melatonin at night time
in the range of few tens of micrograms, it is recommended to start from doses below
1mg and then gradually increase the dose up to 5mg.
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