Light-Dark Cycles

Melatonin is synthesized and secreted during the dark phase of the day. Thus, it is a true circadian rhythm. Melatonin secretion is related to the length of the night.

Light Exposure

Light exposure of the retina alters the amount of serotonin metabolized to melatonin, via the neural pathways that connect the retina to the pineal gland. Exposure to sufficient levels of light at night can rapidly reduce melatonin production.

Electromagnetic Energy

One study on humans who used electric blankets concluded that periodic exposure to even low frequency electric or magnetic fields can significantly affect pineal gland function.

Seasonal Variations

Seasonal changes can affect melatonin secretion patterns by advancing or delaying secretion phase shifts.

Effect of Drugs

Antidepressants and other psychotropic drugs affect the synthesis and release of melatonin. Although tricyclics and fluvoxamine are both associated with increases in mela-tonin secretion in humans, fluoxetine (commonly known as Prozac) reportedly lowers blood melatonin levels.

One group of researchers conjectured that sleep disruption associated with some nonsteroidal anti-inflammatory drugs (NSAIDS) such as aspirin, ibuprofen, and acetaminophen may be a result of decreased prostaglandin production, which can sup-press melatonin secretion. ß-blockers can also significantly alter melatonin levels.

The Role of Melatonin Mood & Behavior

In general, studies have reported decreased nocturnal melatonin levels in patients suffering from depression. In a fascinating study on geomagnetic storms and depression, British researchers found that male hospital admissions with a diagnosis of depression rose. 2% during periods of geomagnetic activity as compared with normal periods. The investigators hypothesized that this increase may have been caused by a phase advance in the circadian rhythm of melatonin production.

Body Temperature

In humans, the lowest body temperature correlates closely with the peak level of melatonin. The ovulatory rise in temperature during the menstrual cycle is also associated with a decline in melatonin secretion levels. Melatonin’s effect on body temperature may be one of the keys of its ability to enhance sleep. In general, a falling body temperature induces sleep, while a rising body temperature provokes wakefulness.

Sleep

Patients with delayed sleep phase insomnia cannot sleep until the early hours of morning. This condition has been treated successfully with exposure to bright light in the early morning to induce phase advances of the clock. An evening dose of 5 mg of melatonin at 11:00 p.m. has also been shown to advance sleep time significantly. l