Another significant result of these experiments was that the youthful pineal gland in the old mice brought about a rejuvenation to the thymus gland. This almost certainly was a causative feature of melatonin's strong positive effect on the immune system. The thymus, we will recall, plays a crucial role in T-cell formation, serving to "incubate" the T-cells and bring them to maturity.

Another study showed that partial sleep deprivation brought about lower melatonin levels, which in turn, brought about reduced activity in the NK (natural killer) cells. The NK cells are the part of the body's army that combats viruses, and most importantly, cancer.

Melatonin has also shown itself to be a very effective antioxidant. Because it can work inside the cell, melatonin is able not only to neutralize free radicals trying to eat holes through the cell's wall, but it can even counter free radicals in the nucleus that are damaging and degrading the cell's DNA.

Although melatonin has shown a minimum of harmful side effects, there are concerns that we would be well advised to keep in mind.

A cautionary note from Dr.Chein:
"In studies using varying doses of melatonin, the only reported side effects included: high-dose-induced headaches, nausea, chronic grogginess, and nightmares. Despite this apparent safety, self-prescribed melatonin users still experience some problems. One of the main problems lies with the over-the-counter varieties of the supplement. Because melatonin is not a regulated substance, almost anyone who wants to, can manufacture it. Some formulations may be poor quality and not completely pure. This increases your risk of experiencing the side effects mentioned above, and some people have reported another problem - that the effect of melatonin wears off suddenly."

Further, to date there are no long term studies on humans that conclusively demonstrate the benefits of melatonin.