Key Takeaway
Melatonin significantly improves sleep quality (PSQI WMD -1.24), with particularly strong effects in people with respiratory diseases and metabolic disorders.
Summary
This systematic review and meta-analysis examined 23 RCTs (from 2,642 screened papers) evaluating melatonin supplementation's effect on sleep quality using the Pittsburgh Sleep Quality Index (PSQI). The study provides condition-specific evidence for melatonin's efficacy.
Overall, melatonin significantly improved sleep quality (WMD: -1.24, 95% CI: -1.77 to -0.71, p < 0.001), though with substantial heterogeneity (I-squared = 80.7%). Subgroup analysis revealed the strongest effects in patients with respiratory diseases (WMD: -2.20) and metabolic disorders (WMD: -2.74), with more modest effects in primary sleep disorders (WMD: -0.67).
Importantly, melatonin did not significantly improve sleep quality in people with mental disorders, neurodegenerative diseases, or certain other conditions, suggesting its benefits are condition-dependent rather than universal.
Methods
- Systematic review of 2,642 papers, 23 RCTs met inclusion criteria
- Pittsburgh Sleep Quality Index (PSQI) as primary outcome measure
- Random-effects meta-analysis
- Subgroup analyses by health condition and intervention type
- Sources of heterogeneity assessed (health status, intervention type)
Key Results
- Overall sleep quality improved: WMD -1.24 (95% CI: -1.77, -0.71, p < 0.001)
- Substantial heterogeneity: I-squared = 80.7%
- Respiratory diseases: WMD -2.20 (95% CI: -2.97, -1.44) - strongest effect
- Metabolic disorders: WMD -2.74 (95% CI: -3.48, -2.00)
- Primary sleep disorders: WMD -0.67 (95% CI: -0.98, -0.37)
- Not significant for mental disorders, neurodegenerative diseases, or other conditions
Limitations
- High heterogeneity across studies (I-squared = 80.7%)
- PSQI is a subjective self-report measure
- Variable melatonin doses and formulations across studies
- Health status significantly moderated effects, limiting generalizability
- Limited number of studies in some subgroup analyses
- Publication bias not fully assessed