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Melatonin, Circadian Rhythm

The Melatonin Circadian Rhythm test measures the levels of melatonin over a complete dark-light cycle. Melatonin is produced during the dark phase of the day by the pineal gland, a small endocrine gland in the brain that regulates the sleep-wake cycle.

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Melatonin has physiological importance in the control of sleep time and duration. It is central to the modulation of both circadian and annual biorhythms and has a remarkably tight association with sleep propensity and thermoregulation. Daytime administration of melatonin can increase drowsiness and lower core body temperature via heat loss induction. It also acts as an antioxidant and plays a role in the regulation of cardiovascular function and female reproductive hormones. If melatonin imbalances occur there can be far-reaching effects, including menstrual difficulties, sleep disorders, depression, and Seasonal Affective Disorder (SAD). The synthesis and physiological use of melatonin are strongly affected by the length of the day, artificial illumination, seasonal changes, and aging. Therefore, accurate measurement of melatonin levels and the circadian rhythm are essential for the development of therapeutic regimes, such as the timing of artificial light and melatonin administration.

Excess melatonin is associated with anxiety, stress, and depression. These elevated levels are also present in those diagnosed with certain types of depression. It has been observed that this form of bipolar disorder might have elevated sensitivity to light, i.e., a greater decrease in melatonin secretion in response to light exposure at night. This should be contrasted with drug-free, recovered bipolar patients, who show normal light sensitivity. Elevated melatonin is also associated with a lowered estrogen/progesterone ratio, inhibition of ovulation, low thyroid, and adrenal function, and hypotension.

Possible Causes of High Melatonin
  • Melatonin of tryptophan supplementation
  • Extended nocturnal dark phase
  • Certain drugs such as MAO inhibitors, fluvoxamine, and desipramine
  • Herbs including St John’s Wort and Cannabis
  • Decreased metabolism by the liver – check glucuronidation or sulphation pathways
  • It may be associated with the seasonal affective disorder (SAD)

Deficient production of melatonin can result in anxiety and mood disorders, lowered basal body temperature, insomnia, and sleep/wake disorders. This disturbance in the circadian rhythm of melatonin may influence other hormones, such as thyroid and testosterone. It may lead to an elevated estrogen/progesterone ratio, decreased cardiovascular and antioxidant protection, and immune suppression associated with cancer.

Possible Causes of Low Melatonin
  • Increasing age
  • Lack of sleep
  • A prolonged light phase of the day
  • Exposure to bright lights or electromagnetic fields, including regular long-haul flights or night shift work
  • Excessive exercise at night
  • Decreased production by the pineal gland or increased metabolism by the liver
  • Stress, especially if high cortisol
  • Certain drugs include SSRIs, benzodiazepines, NSAIDs, anti-hypertensives, beta-blockers, adrenergic, calcium channel blockers, and steroids
  • Excessive coffee, tobacco, and alcohol can lower melatonin
  • High-dose B12 supplementation


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