Melatonin is a hormone that your body produces when it is dark. It regulates your 24-hour internal clock and helps you fall asleep at night.
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Research suggests that melatonin may play a role in other brain and bodily functions, including mood and emotions. However, scientists still do not fully understand these effects.
Some people have reported that melatonin supplementation may exacerbate symptoms of depression by lowering their energy levels. However, there is limited evidence to substantiate these claims.
Other people have proposed that melatonin supplementation could improve depression symptoms in people living with major depressive disorder and other mental disorders. Scientific studies have so far shown mixed results, and more research is needed to see whether melatonin supplementation can be an effective complementary or alternative treatment for depression.
One of the main functions of melatonin is to regulate our biological rhythms. There are two different melatonin production pathways: pineal and extra-pineal.
Pineal melatonin synthesis takes place in the pineal gland of the brain. Darkness at night triggers a pathway that begins in the retina of the eye, travels through our suprachiasmatic nucleus (which regulates circadian rhythms in the body), and ends in the pineal gland, where it prompts melatonin production.
This process typically begins about two hours after nightfall and is known as "dim light melatonin onset." Other external stimuli such as feeding schedules, rest-activity, and social cues also affect this pathway. Melatonin travels around the body from the pineal gland, spreading information about light and darkness and regulating daily functions.
Melatonin plays a vital role in regulating biological rhythms. Biological rhythms determine when certain bodily functions and behaviors occur and keep us 'in time' with the outside world.
However, the interactions between melatonin and our behavior are complex. While melatonin production may impact behavior - by making us want to sleep, for example - our behavior may also impact melatonin production by determining our light exposure, feeding behavior, and activity levels.
Extra-pineal melatonin synthesis occurs in other body parts, including the skin, guts, and lungs. Extra-pineal melatonin only acts locally with no known effects on our biological rhythms.
Scientists have established that depressive states, including mood disorders, are associated with imbalances in hormones and neurochemicals, such as serotonin and dopamine. Recent research has explored whether misalignment of biological rhythms could contribute to these imbalances.
Depressive states can manifest as various behavioral and psychological symptoms and altered bodily functions. They may involve the inability to feel pleasure, feelings of worthlessness, or sleep disturbances.
Depressive states can be symptoms of many kinds of mental disorders, including bipolar mood disorder, major depressive disorder (MDD), and seasonal affective disorder (SAD). Depression can significantly affect someone's daily life, and MDD is the leading cause of disability worldwide.
Experimental and clinical studies suggest that disrupting biological rhythms may increase symptoms of depression and anxiety.
One study found that disrupting the regulation of biological rhythms in rats (affecting the suprachiasmatic nucleus) caused helplessness, behavioral despair, and anxiety-like symptoms. Another study found that rats who lived in 22 hour light and dark phases developed depressive-like symptoms, including the inability to experience pleasure and increased immobility.
In humans, clinical trials have found that dysfunctions in biological rhythms are present in various clinical conditions, including obesity, diabetes, and cancer. Changes in biological rhythms are also associated with mood alterations - in particular, depressive symptoms can come and go with the seasons, in a condition known as seasonal affective disorder (SAD). Moreover, individuals with depressive disorders are more likely to report that their mood varies with the time of day.
Altered melatonin production may disrupt our biological rhythms, causing these mood alterations. At the same time, decreased serotonin levels in people living with depression may affect pineal melatonin production, causing further changes in mood.
Melatonin controls dopamine signaling in certain areas of the brain. Dopamine is a hormone that affects mood, motivation, and the production of other mood-affecting hormones like noradrenaline. Abnormal melatonin levels may affect dopamine signaling, causing mood and behavioral changes.
Melatonin also plays an essential role in our immune system. Concentrations of the stress hormone cortisol are compatible with inflammatory response potentiate melatonin synthesis (but not concentrations associated with chronic unpredictable mild stress).
During an innate immune response, melatonin helps send white blood cells from the bone marrow to the blood and from the blood to the site of injury. For your body to recover from an inflammatory response - and return to normal functioning - melatonin levels have to return to their baseline.
Research has found increased neuroinflammatory responses in a series of neurodegenerative and psychiatric disorders, including major depressive disorder. Animal studies have shown that melatonin treatment significantly abolished several inflammatory effects and decreased depressive symptoms.
This research suggests that melatonin treatment could have an antidepressant effect through its interactions with the immune system.
While treatments for depression are available, scientists have found that their effectiveness varies greatly from person to person. This may be attributable to the wide variety of symptoms that a person with depression can experience - one person's experience of depression may be very different from another.
Selective serotonin reuptake inhibitors (SSRIs) are among the most common depression treatments. SSRIs are antidepressant medications that affect the balance of serotonin in the brain, a hormone that helps regulate mood, sleep, and other basic functions. However, research has found that SSRIs only improve depressive symptoms in about one in five people living with moderate to severe depression.
Because of this, scientists have trialed melatonin treatment for depression. Melatonin treatment typically involves taking melatonin supplements once or twice a day, including once around bedtime.
A recent systematic review explored the effects of melatonin treatment on individuals living with different types of depression. The results of clinical trials are mixed. While some studies found no antidepressant effect, others found significant improvements in depressive symptoms.
In particular, one study found that a combination of slow-releasing melatonin and buspirone had a significant antidepressant effect in the context of depression. Another found that taking melatonin supplements twice daily improved symptoms of seasonal affective disorder.
A separate review into the effects of melatonin supplementation in clients with co-morbid conditions offered similarly mixed results. Two studies found melatonin treatment to improve depressive symptoms in older adults with sleep complaints among individuals with delayed sleep-phase syndrome. However, several other studies found no significant effects.
Research and interest in melatonin treatment are growing. Melatonin is recommended as an adjuvant treatment for sleep disorders in children and adolescents, particularly those with autism. Research has also found that melatonin may lead to significantly advanced sleep onset in individuals living with delayed sleep-phase syndrome.
However, even in the context of sleep disorders, studies show mixed results, and any evidence should be carefully examined.
Some people report certain adverse side effects from melatonin supplements, including:
A few people also report short-term depression as a side effect. The reason for this is unclear - perhaps side effects like headaches and sleepiness exacerbate depressive symptoms. Some research has also found that people living with depression have higher melatonin levels than healthy individuals. However, other studies have found that melatonin levels are lower.
So far, there is no clear agreement between studies on the relationship between melatonin levels and depression. Moreover, there is no evidence to suggest that taking melatonin can cause the onset of mental health issues like major depressive disorder or seasonal affective disorder.
Melatonin plays an important but complex role in our bodies. It helps regulate our biological rhythms and affects our immune response. These roles offer potential as a treatment for mood disorders, including depression.
However, while some studies suggest melatonin may have antidepressant effects, the evidence is unclear. The complexity and intricacies of our biological clocks and circadian rhythms make it difficult to pinpoint causal effects, and clinical trials offer mixed results.
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Hopefully, further scientific research will help us to better understand the relationship between melatonin and depressive states and explore the potential of melatonin treatment.
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