The Human Body

Melatonin

Melatonin, naturally occurring hormone that is released into the bloodstream during the hours of darkness. While scientists continue to study the function of melatonin in humans, they believe the hormone plays a role in the body’s circadian rhythm. This rhythm regulates the physiological functions that occur in the body within a 24-hour period, such as sleep-wake cycles, fluctuations in body temperature, heart rate, and blood pressure. More recently melatonin has become a popular nonprescription dietary supplement with the alleged ability to combat a variety of health problems.

Melatonin is produced by the pineal body, a cone-shaped gland about the size of a pea that is situated near the center of the brain. The release of melatonin from the pineal body into the bloodstream is orchestrated by the hypothalamus, a region of the brain that governs the body’s internal environment to maintain temperature, water balance, and hormone balance. The hypothalamus receives cues about the amount of sunlight that is absorbed by the eye—darkness causes the hypothalamus to stimulate melatonin release while light suppresses its release.