Previous research has indicated that melatonin supplementation could lead to an improvement in blood lipid levels, but "current evidence from randomised controlled trials (RCTs) is inconsistent".
As such, researchers at Iran's Shiraz University of Medical Sciences and Torbat Heydariyeh University of Medical Sciences conducted a systematic review to analyse RCTs studying how melatonin supplementation affected blood lipids.
They assessed papers published between 1997 and 2014, from eight studies involving participants between the ages of 16 and 74 from Iran, Poland, the US, Brazil and Mexico. One study had been conducted exclusively on men; the others involved both male and female subjects.
The researchers then wrote that their meta-analysis "suggested a significant association between melatonin supplementation and a reduction in triglycerides and total cholesterol levels".
In experimental studies, melatonin's lipid-reducing mechanisms were attributed to its suppression of visceral fat, which enhanced insulin sensitivity, increased lipoprotein lipase (LPL) activity, decreased lipolysis in adipose tissue, prevented cholesterol absorption and synthesis, improved LDL receptor activity, and inhibited metabotropic receptors (which help transport fatty acids).
Additionally, there was a "noticeable reduction" of VLDL (very low-density lipoprotein) cholesterol after melatonin supplementation. This effect was said to be induced by lower VLDL secretion from the liver but also from the intestine, which is consistent with intestinal cholesterol absorption being suppressed.
They added that their sub-group analysis showed a considerable decrease in triglycerides in those supplemented with 8mg doses daily for eight weeks.
They also noted a decrease in total cholesterol in participants whose total cholesterol levels at baseline were 200mg/dL and who had been supplemented with 8mg of melatonin daily.
At the same time, however, they observed that while melatonin supplementation had resulted in minor improvements in LDL and HDL cholesterol, the impact was not significant.
The researchers wrote that overall, "the triglyceride- and total cholesterol-lowering effect of melatonin, along with its minor effect on improving LDL and HDL cholesterol, and other findings which showed that melatonin can protect LDL from oxidation may contribute to its promising beneficial role in atherosclerosis prevention, given that LDL oxidation is an important activating step in the pathogenesis of atherosclerosis".
They further stated that melatonin's ability to lower plasma triglyceride levels is "an important consequence due to the remnant lipoprotein particles which are triglyceride-rich lipoproteins" that are involved in the pathophysiology of atherosclerosis.
Additionally, they found a large amount of evidence of melatonin as a strong antioxidant.
They concluded: "Further studies are required to determine the benefits of melatonin on lipid profile.
"The positive effect of melatonin is more evident in higher doses and longer duration(s). Additional high-quality, well-designed studies should be performed to approve our findings."
Source: Clinical Nutrition
"Effects of melatonin supplementation on blood lipid concentrations: A systematic review and meta-analysis of randomized controlled trials"
Authors: Mohsen Mohammadi-Sartang, et al.