Melatonin, a hormone produced by the pineal gland, is best known for regulating sleep and the circadian rhythm
Melatonin can also exert anti-inflammatory, antioxidant, immunomodulatory and cardioprotective effects.
Experimental studies show that melatonin enhances insulin sensitivity, increases activity of lipoprotein lipase, decreases lipolysis in adipose tissue, increases conversion of cholesterol to bile acids, and protects LDL from oxidation.
Clinical trials on the effects of melatonin in dyslipidemia have produced mixed results, so researchers conducted a systematic review and meta-analysis to better assess the effect of melatonin supplementation on blood lipid levels.
The final analysis included eight randomised controlled trials of melatonin supplementation.
Four trials were classified as high quality (Jadad score <3) and four were classified as low quality (Jadad score <3).
The outcomes included plasma triglycerides, total cholesterol, LDL-cholesterol and HDL-cholesterol. Weighted mean differences (WMD) and 95% confidence intervals (Cis) were calculated to represent effect sizes.
Meta-analysis suggested a significant association between melatonin supplementation and reduced triglyceride levels (WMD: -31.54mg/dL; 95% CI, -50.71 to -12.38; p=.001) as well as reduced total cholesterol levels (WMD: -18.48 mg/dL; 95% CI, -35.33 to -1.63; p=.032). No significant effect was found on LDL-cholesterol or HDL-cholesterol.
Subgroup analyses were conducted on the following variables: dosage of supplementation, intervention duration, and baseline lipid profile.
These analyses revealed that triglyceride levels were significantly reduced only at melatonin dosages >8 mg/day and when the trials lasted for >8 weeks. Total cholesterol levels were significantly reduced only at dosages >8 mg/day and when total baseline cholesterol levels were >200 mg/dL.
The results of this meta-analysis suggest that melatonin supplementation at dosages >8 mg/day and for >8 weeks may have beneficial effects on plasma triglycerides and total cholesterol levels but is unlikely to affect LDL or HDL concentrations.
Results also suggest that melatonin supplementation may only improve blood lipids in patients with baseline elevated cholesterol.