If you’re like me and thought melatonin is basically all about promoting sleep, get ready to look at melatonin in a whole new light. I’ve discovered that supporting sleep is only the tip of the iceberg when it comes to the many functions of melatonin, and thought I’d share my insights with our NeuroScience friends.
Okay, so let’s start with sleep. Following the onset of darkness, there is a surge in melatonin secretion from the pineal gland that initiates the onset of sleep. Circulating, pineal-derived melatonin continues to rise until the middle of the night and then falls again by morning. This nocturnal elevation is essential for sleep and for regulating the body’s circadian rhythm. Messing with this diurnal variation in melatonin output disrupts not only sleep, but numerous other biological processes that follow a circadian pattern as well.
In addition to promoting sleep onset, melatonin supports sleep quality by increasing levels of gamma-aminobutyric acid, or GABA, in the hypothalamus (Xu et al., 1995). Melatonin also reduces the negative effects of glutamate signaling (Kumar and Singh, 2009). Consequently, melatonin can reduce stress and anxiety. And by promoting restful, restorative sleep and reducing stress, melatonin can help prevent short-term cognitive deficits.
Now let’s move beyond sleep. Melatonin’s well-documented antioxidant effects are at least as important as its sleep benefits. These effects are triggered by (1) its own intrinsic antioxidant activity; (2) upregulation of other antioxidant systems such as glutathione peroxidase, glutathione reductase, and superoxide dismutases; and (3) down-regulation of pro-oxidative enzymes (Hardeland and Pandi-Perumal, 2005; Kumar and Singh, 2009).
But the marvels of melatonin aren’t restricted to the brain. Melatonin can aid in digestion and may be useful in managing constipation and other smooth muscle-related health issues (Pozo, 2010).
You may have noted that several conditions I’ve mentioned in this post occur more frequently with aging. Probably not coincidentally, nighttime melatonin production decreases as we get older. Melatonin may combat the aging of the immune system, or immunosenescence (Cardinali, 2008). And finally, the observation that calorie restriction can help prolong lifespan has recently been complemented by observations that hunger boosts gastrointestinal melatonin production (Bubenik and Konturek, 2011). Coincidence? Maybe, but given a choice between melatonin and feeling hungry every day…I’ll take the melatonin!