However, a study by Chester A. Ray, Ph.D., associate professor of medicine, Penn State College of Medicine, Penn State Milton S. Hershey Medical Center suggests that melatonin supplements may make symptoms worse for the half a million people many of them women and the elderly with orthostatic intolerance, a condition in which the cardiovascular system cannot maintain adequate blood pressure and blood flow to the brain when a person stands, causing dizziness and fainting.
"Melatonin supplements can hinder nervous system responses that enable the body to compensate for the drop in blood pressure when a person moves from a seated to standing position," Ray said. The study titled, "Melatonin attenuates the sympathetic nerve responses to orthostatic stress in humans," was published in the Sept. 15 issue of the Journal of Physiology (London).
In addition to its use here on Earth, melatonin also is taken by astronauts in space, two-thirds of whom experience orthostatic intolerance immediately after touchdown on Earth.
"When astronauts return to Earth, there is a chance that, for safety reasons, they will need to make a quick exit from the spacecraft," Ray said. "This study suggests that taking melatonin supplements for sleep could exacerbate orthostatic intolerance, making them unable to evacuate the shuttle and compromising their safety."
Melatonin is a hormone made by the pineal gland in the brain and secreted at night on a circadian, or 24 hour, cycle, to make people feel sleepy. Available in synthetic form, dietary supplements of melatonin have been linked to improved sleep, prevention of jet lag, and more. Studies have shown that melatonin supplementation may reduce blood pressure and decrease blood plasma levels of norepinephrine, a neurotransmitter responsible for raising blood pressure.