What is melatonin?
Melatonin is a hormone produced by the pineal gland and has an important role in circadian rhythms. The daily rhythm of melatonin secretion is controlled by an inbuilt, free running pacemaker, the suprachiasmatic nucleus, and is synthesized from the amino acid tryptophan. Melatonin synthesis is controlled by exposure to cycles of light and dark, and occurs independently of sleep.
What part does melatonin play in regulating sleep?
Melatonin promotes sleep and its secretion increase soon after the onset of darkness, helping to keep us asleep at night. Melatonin production usually peaks between midnight and 2am, then starts to fall and is low during the day. It also helps reduce core body temperature, which helps induce sleep. However, sleep is possible even when melatonin levels are low. People who have their pineal gland removed have only minimal disruption in sleep.
Does melatonin have any other effects on the body?
Laboratory experiments have shown that melatonin has antioxidant effects and suppresses the growth of some cancer cells. Laboratory findings also show it has anti-inflammatory effects. When melatonin is administered as a drug, it has been shown to decrease levels of the female hormones progesterone and oestradiol. It also enhances the secretion of prolactin (hormone produced by the pituitary gland). Melatonin may reduce the sensitivity if the body to insulin, which can raise blood levels.
Other chemicals involved in sleep. A large number of neurotransmitter and hormones regulate the sleep wake process in the brain and nervous system. Their major functions are listed below.
Noradrenaline/ Adrenaline the fight or flight chemicals. These stimulate, enhance or prolong a waking, attentive, and aroused state.
Dopamine Arouses your cerebral cortex (grey matter), involved in the regulation of movement and responsiveness.
Acetylcholine Activates your cerebral cortex, increase vigilance. Levels are highest when awake and in REM sleep.
Histamine Actives cerebral cortex during wakefulness.
Hypocretin (Orexin) – Promotes wakefulness and prevents sleep, including REM sleep. Stimulates energy metabolism and regulates appetite.
Glutamate – Stimulates your central nervous system and activates your cerebral cortex. Critical to wakefulness.
GABA (gamma amino butyric acid) Inhibits wakefulness. Sleep inducing drugs enhance the action of GABA to cause sleepiness and drowsiness.
Galanin Inhibits wakefulness.
Adenosine Induces sleep and is blocked by caffeine. Levels build up during the day and drop during the sleep.
Serotonin Has a tranquillizing effect. May prepare brain and body for slow wave sleep by reducing the body’s activating systems.
Insulin – accumulates during active waking periods with food intake and can lead to induction of sleep subsequently.