As discussed above, melatonin has been shown to have numerous health benefits, as an immune stimulant, antioxidant, and cardiovascular ally. But it is crucial in the induction of sleep and the regulation of the circadian rhythm.
When it’s dark, the pineal gland secretes melatonin in extremely minute amounts—blood levels of melatonin are measured in picograms, that is, trillionths of a gram. The actual amounts depend on age and other factors, but between five and ten times more melatonin is released at night than during the day. Melatonin is the antithesis of another hormone, adrenaline, produced by the adrenal glands. As melatonin enters the bloodstream, it begins to slow down the waking (alpha) brain waves. Subsequently, the heart rate decreases, muscles relax, blood pressure drops, and the body begins to enter the stages of sleep.
The average blood levels of melatonin throughout the day mirrors typical circadian rhythms. Low amounts of melatonin correspond to the periods of heightened alertness; high amounts of melatonin relate to periods of drowsiness and sleep. Between 7 a.m. and 2 p.m., melatonin is at its lowest level, below ten picograms per milliliter (pg/ml) of blood. From 2 p.m. to about 8 p.m., melatonin levels rise slightly, as the pineal gland begins production of the sleep hormone. Melatonin reaches its peak (70 pg/ml) in most people at approximately 2 a.m., flattens for a couple of hours, then around 4 a.m. begins a dramatic drop to its lowest levels.
Production of melatonin not only varies during the 24-hour cycle, it also fluctuates during our life span. Newborns produce very low amounts of melatonin, usually sleeping 16 to 18 hours a day, spread out over six to seven naps. By the age of three months, they begin producing greater levels of the hormone; it is also during this time that babies begin to sleep through the night and become more alert during the day. Melatonin levels surge from then on, peaking before the age of ten at about 125 pg/ml. Children during this time sleep ten or more hours a night and undergo a dramatic growth spurt, which is aided by sleep.
When adolescents reach puberty, a time when high levels of sex hormones are being released, melatonin levels begin to decline and continue thus for the rest of the person’s life. Simultaneously, for reasons scientists are still researching, other hormones begin to dip, including testosterone, estrogen, growth hormone, and DHEA. Between the ages of 20 and 30, melatonin levels are about 40-60 pg/ml; by age 50, levels are below 20 pg/ml. People over 60 produce negligible amounts of melatonin, below 10 pg/ml.
