Melatonin

I. Basic Information

1. Chemical Nature

Melatonin is an indole heterocyclic hormone secreted by the pineal gland in the brain. Its chemical name is N-acetyl-5-methoxytryptamine, also known as pineal gland hormone or melatonin hormone. Its molecular structure is synthesized through a four-step process—hydroxylation, decarboxylation, acetylation, and methylation—using tryptophan as the raw material, and is ultimately stored and released within the pineal gland.

2. Secretion Rhythm

Melatonin secretion exhibits a distinct circadian rhythm:

Nocturnal Activity: Secretion increases in dark environments, peaking at 2-3 AM to induce sleep.

Diurnal Suppression: Light exposure (especially blue light), perceived by the retina, inhibits melatonin synthesis to maintain wakefulness.

Age-Related Changes: After age 35, secretion declines by 10%-15% every decade, with significantly reduced levels in the elderly, leading to sleep disturbances.

3. Metabolic Pathway

Melatonin is metabolized in the liver by cytochrome P450 enzymes, primarily yielding 6-hydroxymelatonin as the main product, and is ultimately excreted via urine. Liver injury may impair its metabolic efficiency.

II. Core Applications

1. Improving Sleep Quality

Reducing Sleep Onset Latency: Regulates the sleep-wake cycle and decreases pre-sleep wakefulness.

Prolonging Deep Sleep Stages: Lowers the frequency of nocturnal awakenings, enhancing sleep continuity, particularly for circadian rhythm disorders (e.g., jet lag, shift work).

Dosage Recommendation: Physiological requirements range from 0.1–0.3 mg, while commercially available supplements often contain higher doses (0.5–5 mg). It is advisable to start with a low dose to avoid daytime drowsiness caused by overdose.

2. Regulating Circadian Rhythms and Biological Clocks

Adapting to Environmental Changes: Assists travelers crossing time zones in rapidly adjusting their biological clocks and alleviating jet lag syndrome.

Treating Delayed Sleep Phase Syndrome: Demonstrates significant efficacy for sleep disorders in adolescents and adults.

3. Antioxidant and Anti-Aging Effects

Scavenging Free Radicals: As a potent free radical scavenger, melatonin penetrates cell membranes and the blood-brain barrier to protect DNA, mitochondria, and lipids from oxidative damage.

Delaying Aging: Animal studies indicate that melatonin supplementation extends lifespan and improves metabolic function, outperforming vitamins C/E and grape seed extract.

4. Immunomodulation

Enhancing Immune Function: Reduces infection risk by regulating cellular immunity (e.g., T cell and NK cell activity) and humoral immunity (e.g., antibody production).

Anti-Inflammatory Effects: Inhibits the NF-κB signaling pathway, reducing the release of inflammatory factors (e.g., IL-1β, TNF-α) and alleviating chronic inflammation.

5. Neuroprotection

Reducing Neuronal Damage: Protects nerve cells and improves cognitive function in Parkinson’s and Alzheimer’s disease models through antioxidant and anti-inflammatory mechanisms.

Antiepileptic Effects: Lowers seizure frequency by regulating the glutamate/GABA balance.

6. Cardiovascular Protection

Regulating Blood Pressure and Heart Rhythm: Lowers nocturnal blood pressure and prevents myocardial infarction and ischemic heart disease by inhibiting sympathetic nervous activity.

Anti-Atherosclerotic Effects: Inhibits LDL oxidation and vascular smooth muscle cell proliferation, reducing plaque formation.

7. Other Applications

Adjunctive Antitumor Therapy: Suppresses tumor cell proliferation (e.g., breast and prostate cancers) by modulating MAPK/PI3K signaling pathways.

Heavy Metal Detoxification: Chelates heavy metal ions such as cadmium and lead to reduce toxic damage.

Radiation Protection: Improves survival rates in irradiated animals and protects immune system function.

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