All living beings, including humans, animals and plants naturally live by circadian rhythms. Circadian rhythms consist of a 24 hour physiological cycle that is modulated by our environment and external cues such as sunlight and temperature. Circadian rhythms are important because they determine when to sleep and eat.
Brain wave activity, the hormones we produce, and the cells that we regenerate, along with a myriad number of other biological activities are linked to this daily cycle.
Our pattern for waking during the day when it is light and sleeping at night when it is dark is a completely natural part of human life. Before humans had artificial light or even fire, they would have retreated in the dark to sleep and then come out to find food when it was light enough to see. We have been following that pattern for many millennia.
The Relationship Between Melatonin & Darkness
Recently scientists have started to understand the alternating cycle of sleep and waking, and realized that human sleep is regulated by exposure to light or darkness. They have discovered that exposure to light stimulates a nerve pathway from the eye to an area in the brain called the hypothalamus.
Within the hypothalamus the supra-chiasmatic nucleus (SCN) sends out signals to other parts of the brain that control our hormones, temperature and those other functions that help us feel wide awake or half asleep.
The SCN works a little like a clock. It sets in motion a rhythm of activities within the body. At first light the SCN asks for functions such as a rise in body temperature, or the release of hormones such as cortisol which stimulate us. At the same time the SCN will delay the production of sleep inducing hormones such as melatonin until darkness arrives.
Melatonin is a hormone naturally produced by the pineal gland, located in the centre of the brain. The pineal is inactive during the day but once the sun goes down it is switched on by the SCN and it begins to produce melatonin. The hormone is released into the blood and melatonin levels will begin to rise from around 9 pm in the evening.
You feel the effect as a lack of alertness kicks in and sleep begins to feel like a good idea. These levels of melatonin then stay elevated for 12 hours until the light of the new day causes the SCN to switch the pineal gland back off.
Bright light inhibits the production of melatonin – like a vampire it only comes out at night. Even if the pineal gland is switched on by the SCN, if a person is in a bright environment with a lot of lighting, melatonin will not be produced. Light needs to be dim in order for the hormone to be released. The secretion of melatonin depreciates with age. Children secrete ore and therefore sleep longer.
Over the Counter Melatonin
Melatonin is available to buy over the counter unlike many other hormones. This is because melatonin is naturally occurring in some foods. It is therefore licensed to be available in some vitamins and minerals. If you take melatonin there are a few things you need to be wary of. Synthetic melatonin is produced in factories that may not be regulated and listed dosage may not be accurate.
In any case, a supplement will raise melatonin levels beyond what one would expect to see naturally. A typical dose of 1 to 3 mg can elevate blood melatonin levels to 1 to 20 times normal. Side effects, although uncommon, can include fatigue and depression.
In animals, melatonin can cause changes in blood pressure and affect fertility. In humans potential risks exist for people with heart-related problems, hypertension, stroke, kidney disease and sleep apnoea as well as for women of child-bearing age.
It you are taking melatonin for a sleep problem, be aware that the correct dosage, method and time of day it is taken must be appropriate, otherwise you risk resetting your biological clock in an undesirable way. How much to take, when to take it, and its effectiveness, is only just beginning to be understood.
Research data suggests that melatonin does aid sleep in some people although tests have found that there is no discernible difference between using melatonin and a placebo. Other evidence suggests that exposure to light may be more effective. Overall, research has indicated that improved sleep occurs when melatonin is taken at the appropriate time for jet lag and shift work.
Melatonin might help shift workers on irregular shifts who need to adjust their schedules because at the right dose it advance or delay the sleep-wake cycle. The effect can last for six hours. Taken at the wrong time melatonin can cause fatigue, promote drowsiness, reduce reaction time, reduce vigilance and decrease vigour during the day.
Other studies have found that melatonin can shorten the amount of time it takes to get off to sleep while reducing the number of times one awakes, but again other research shows no benefits.
Studies involving people with insomnia were again inconclusive with people over 50 seeing restoration of their sleep efficiency and improved sleep. Elsewhere, while sleep onset improved, melatonin did not help people stay asleep or alert throughout the day.
For those deficient in melatonin, and for those suffering insomnia, a supplement starting at 3mg for 2-4 weeks is sensible and something most doctors would agree is safe. However, there is a need for larger scientific studies to demonstrate how effective melatonin is, and whether it is safe to use in the long term – what dosage to take and how long for.