褪黑素：剂量、副作用与睡眠科学

Melatonin is a hormone naturally produced by the pineal gland in response to darkness. It does not directly induce sleep — rather, it signals to the body that it is nighttime, helping regulate the circadian rhythm:

• Natural production: Melatonin levels rise in the evening (around 9-10 PM), peak at 2-4 AM, and fall to low levels by morning. Light exposure suppresses production.
• Supplement mechanism: Exogenous melatonin works primarily as a chronobiotic (circadian rhythm regulator) rather than a sedative. This is why it is most effective for circadian rhythm disorders.

What melatonin is most effective for:

• Jet lag: A 2002 Cochrane review found melatonin significantly reduces jet lag symptoms, especially when crossing 5+ time zones traveling east.
• Delayed sleep phase disorder: When your natural sleep time is significantly later than desired, melatonin helps shift the circadian clock earlier.
• Shift work: Helps promote sleep during daytime hours for night shift workers.
• Age-related insomnia: Natural melatonin production decreases with age, making supplementation more beneficial for older adults.

For general insomnia unrelated to circadian rhythm issues, melatonin's benefits are more modest. WAYJET's Health Chat can help assess whether your sleep issues are circadian-related or driven by other factors.

The most common mistake with melatonin is taking too much. Research consistently shows that less is more:

• Optimal dose: 0.5-3mg for most adults. A 2005 study in Sleep Medicine Reviews found 0.3-0.5mg replicated physiological melatonin levels and was effective for sleep onset.
• The problem with high doses: Supplements commonly contain 5-10mg, which is 10-20x the physiological dose. High doses can cause next-day grogginess, vivid dreams/nightmares, and may actually disrupt sleep architecture.
• Study findings: A 2001 MIT study found 0.3mg melatonin was as effective as 3mg for improving sleep in older adults, with fewer side effects.

Timing is crucial:

• For falling asleep: Take 30-60 minutes before desired bedtime
• For jet lag: Take at the desired bedtime in the new time zone for 3-5 nights
• For shifting sleep earlier: Take 3-5 hours before your current natural sleep time at a very low dose (0.3-0.5mg)

Extended-release vs. immediate-release:

• Immediate-release: Best for sleep onset difficulties
• Extended-release: Better for sleep maintenance (waking during the night). May be more appropriate for older adults.

Melatonin is generally well-tolerated at appropriate doses, but several considerations apply:

• Common side effects: Daytime drowsiness (most common, especially at high doses), headache, dizziness, nausea. These are typically dose-related and resolve with dose reduction.
• Vivid dreams: Melatonin increases REM sleep, which can intensify dreams. Some people find this pleasant while others find it disturbing.
• Hormonal considerations: Melatonin interacts with reproductive hormones. High doses may affect menstrual cycles, and animal studies suggest potential effects on puberty timing — this is why many sleep experts recommend caution with long-term use in children.

Drug interactions:

• Blood thinners: May increase bleeding risk when combined with warfarin or antiplatelet medications
• Diabetes medications: Melatonin may affect blood sugar levels. Monitor glucose closely.
• Immunosuppressants: Melatonin has immune-stimulating properties and may interfere with immunosuppressive therapy.
• Blood pressure medications: May reduce the effectiveness of some antihypertensives while enhancing the effect of calcium channel blockers.

Quality concern: A 2017 study in the Journal of Clinical Sleep Medicine tested 31 melatonin supplements and found actual melatonin content ranged from -83% to +478% of what was labeled. Choose products with USP or NSF certification.