Melatonin, known to us lab geeks, as 5-methoxy-N-acetyltryptamine, is a hormone found in most animals and humans.

Melatonin participates in the regulation of the circadian rhythms of several biological functions. Melatonin also functions as an antioxidant, with primary functions of protecting nuclear and mitochondrial DNA. Melatonin is important in these areas, because free radical damage to DNA can result in cancers and other dysfunctions of the affected cell. The protection that melatonin offers to DNA, helps to maintain the integrity of the cell. If melatonin cannot completely prevent free radical damage to cellular DNA, the cell has backup proteins, which usually repair the damaged sequence. We are fortunate that we have extra backup systems in place, in the case of one strategy being overwhelmed by chemical insult.

Once melatonin reacts with a free radical, its' job is done and the resultant "melatonin- free radical" complex is then, removed from the cell as a waste product. In this respect, melatonin differs from other antioxidants, in that, they may undergo several cycles of inactivating free radicals before they are rendered incompetent as antioxidants.

In humans, melatonin is produced in the pineal gland of the brain, the retinae and lens of the eyes, and gastrointestingal tract. The cells of these tissues manufacture melatonin from from the amino acid, tryptophan.

Melatonin production in the pineal gland is controlled by the hypothalamus. The hypothalamus, on the other hand, is influenced from nerve impulses from the retinae, located at the back of the eyes. Since the retinae sense light and dark patterns (night and day), they transmit this information to the hypothalamus. The hypothalamus in turn, then "prompts" the pineal gland to produce melatonin. This is what's known as a feedback cycle: Change the lighting conditions in your environment, and this will ultimately modulate your melatonin levels. Melatonin from the pineal gland functions as an endocrine hormone: It leaves the pineal gland, enters the circulatory system and ultimately affects many cell types throughout the body. since it is released into the blood. Melatonin produced by the retinae and the gastrointestinal tract functions as a paracrine hormone: it affects only local cells and tissues.

Melatonin is also produced by rice, and other plants. This melatonin seems to be effective to a degree in humans.

We can also synthesize melatonin in the laboratory. This has pharmaceutical applications, as the use of melatonin as a drug can modulate the circadian clock to environmental cycles. Since melatonin can cross the blood brain barrier, melatonin is sometimes suitable for the treatment of insomnia.

Melatonin can be purchased as a supplement in many countries. However, it is banned from over the counter sales in some countries. Perhaps, this is because since melatonin can enter the brain, it can affect the mental state.