Melatonin And Other Brain Chemicals - The Influence Of Your Biological Rhythms: Chronic Fatigue

Content provided by the Faculty of the Harvard Medical School

Melatonin and other brain chemicals

One way that light influences your alertness is through melatonin, a hormone that induces drowsiness. Melatonin is produced in a predictable daily rhythm by the pineal gland, located in the middle of the brain, between the two hemispheres. Cells in the suprachiasmatic nucleus receive signals from the eyes about the amount of light in the environment, and send signals to the pineal gland that influence the gland's production of melatonin. Levels of melatonin begin climbing after dark and ebb after dawn. Scientists think that the daily light-sensitive cycles of melatonin help keep the sleep/wake cycle on track.

In addition to melatonin, other chemicals in the body influence our state of alertness. Several neurotransmitters (chemical messengers) play a role in arousal. Norepinephrine, epinephrine (often called adrenaline), and dopamine stimulate wakefulness. Adenosine and gamma-aminobutyric acid (GABA) are believed to promote sleep. Individuals vary greatly in their natural levels of neurotransmitters and in their sensitivity to these chemicals.

Because of these and other differences, people vary in their energy levels. Some people are naturally more energetic than others. Just because the person sitting next to you at work (or sitting across the table from you at breakfast) has more mental or physical energy than you do doesn't mean that there's something wrong with you. It could simply mean that you are at the lower end of the normal energy spectrum or that you're not a "morning person" and your alertness rises later in the day. But it's not normal to lack enough energy to get through the day. If you feel physically weak in the early part of the day, if you become fatigued soon after starting an activity, or if you are unmotivated or mentally weary much of the time, you need to find out why.

Last updated:	January 23, 2007