The pineal gland is a very small gland located within the brain. It produces the hormone melatonin that controls body rhythms, in particular our internal body clock and our sleeping and waking patterns. It may also play a role in a person's sexual development.

In the dark, the pineal gland is stimulated to make and release melatonin. In daylight this production of melatonin is reduced. Most recently it has been suggested that melatonin may be beneficial in the treatment and avoidance of jet lag, and taking it may slow down the ageing process. However, just how true these claims are is still being debated and researched.

But recent research does seem to be pulling together a variety of roles for the pineal gland and melatonin, from regulation of a large number of circadian rhythms, to control of other hormone systems, and modulation of the immune system. It may help to protect against cancer (a number of cancers, such as breast, prostate and colon, are more common among night workers or those whose circadian rhythms are disrupted) and it seems to be essential for pregnancy to have a successful outcome (the mother's melatonin can pass across the placenta and may help to correct complications that result from problems such as pre-eclampsia or fetal brain damage).

In ancient times the pineal gland was known as the 'third eye' and was also thought to have mystical powers. In birds and other animals the pineal gland contains magnetic material and is a centre for navigation.

Researchers are still looking to find whether this is the same in humans, and, if so, then the pineal gland may be our unconscious navigational system. All in all, currently very little is known about the pineal gland - but as research continues it may turn out to be very important indeed.

This article was last medically reviewed by Dr Trisha Macnair in June 2008