The Relationship Between Melatonin, Dopamine, and Sleep
A well regulated sleep schedule is imperative to a healthy lifestyle, but it is not always attainable by the circadian rhythm alone. People may struggle with developing and maintaining a healthy sleep schedule for a number of reasons including stress, anxiety, depression, jet lag, diagnosed sleep disorders, etc. These are varied and multifaceted health issues, yet understanding sleep disorder and potential solutions for it requires a fundamental understanding of the neurotransmitters at play in any or all of these scenarios.
The pineal gland is an endocrine gland in the human brain which is responsible for establishing and maintaining circadian rhythm in the human body. The circadian rhythm is a natural and internal cycle that repeats every 24 hours and regulates the sleep-wake cycle in the human brain. The simplest way to think about the circadian rhythm is in terms of two cycles: the light and dark cycle. The pineal gland translates light signals initially received by the retina in the eye into neurotransmitters interpretable by the brain. Darkness, or the lack of light signals received by the retina, prompts an increase in the natural production of the hormone melatonin which regulates the body’s metabolic activities during sleep. Towards the end of the dark cycle, the pineal gland receives light signals which prompt a decrease in the natural production of the hormone melatonin.
On a more microscopic level, there is another hormone, namely norepinephrine, that is involved in the synthesis of melatonin. By binding to its receptors, norepinephrine releases melatonin, yet it is not always so simple. New scientific research has proven the interaction of norepinephrine receptors with dopamine receptors. When dopamine interacts with these joint receptors or “heteromers,” the effects of norepinephrine are inhibited, resulting in a decrease in the production and release of melatonin. Applying this relationship in the opposite direction, one might hypothesize that an increase in melatonin levels may cause a decrease in dopamine levels to keep the system balanced. Scientists have explored this idea with new research in developing studies.
In a study of male Syrian hamsters, researchers discovered that by administering daily doses of melatonin over the course of five weeks, they decreased the dopamine content of the posterior pituitary in the hamsters by more than 50%. These observations give weight to the hypothesis that melatonin supplementation has an inhibitory effect on the regulation of dopamine in the brain. Though this study certainly does not verify this hypothesis, it should prompt researchers to further investigate the relationship between the hormone melatonin and its effect on other hormones and neurotransmitters in the brain.
In the meantime, it is always safest to err on the side of caution, especially considering the fact that the U.S. Food and Drug Administration (FDA) does not regulate melatonin in the same way it does other prescription or over-the-counter medications. Someone struggling with developing a healthy sleep schedule should weigh the risk of supplementing the hormone melatonin on a personal level, making note of medications he or she already takes regularly. Medications to be cautious of taking melatonin supplements with include blood thinners, diabetes drugs, immune-system suppressants, anti-seizure drugs, and some contraceptives. Symptoms to be weary of include nausea, dizziness, headache, and sleepiness. A conversation with a medical professional should take place before continuing to use melatonin supplements if an individual experiences any of these symptoms or is prescribed these medications. Exploring natural remedies is always a viable option and eliminates all the risk associated with melatonin supplementation presented above. Sticking to a premeditated sleep schedule, creating a comfortable bedroom space with lighting conducive to peaceful sleep, limiting caffeine intake, and avoiding sleep disruptors such as cigarettes, alcohol, cellphones, and heavy meals in the hours before one goes to sleep are all lifestyle changes that may fix a sleep schedule without the need and the risk of melatonin supplementation.
References:
https://www.healthline.com/health/dopamine-vs-serotonin#sleep
https://www.livescience.com/21050-feel-good-brain-chemical-s-role-in-sleep.html
https://westvalleymedctr.com/blog/entry/4-reasons-to-be-cautious-about-melatonin
https://pubmed.ncbi.nlm.nih.gov/12043836/
