Meta-Analysis of Experimental Studies of the Effect of Melatonin Monotherapy on the Level of Circulation Triglycerides, Cholesterol, Glucose and Insulin Depending on the Diet of Rats

Abstract

It is known that melatonin modulates the daily and seasonal rhythms of metabolism. However, the effect of long-term intake of exogenous melatonin on the parameters of lipid and carbohydrate metabolism in various diets is still unclear. In our work, we conducted the meta-analysis of 53 publications investigating the effect of melatonin monotherapy on lipid and carbohydrate metabolism in rats kept on a standard diet (44 publications), as well as diets with a high content of fructose (7 publications), fats (11 publications) and cholesterol (5 publications). According to the literature, high fructose diet caused a significant increase in the levels of triglycerides, glucose and insulin in rats. In rats fed high fat diet, an increase in triglycerides, total cholesterol (TC), insulin, and a decrease in high-density lipoprotein (HDL) was observed. In rats kept on high cholesterol diet an increase in the level of TC and a decrease in the concentration of HDL was observed. Melatonin therapy reduced triglyceride, TC, and insulin levels but did not alter glucose levels in rats fed diets rich in fructose and fats. On a cholesterol-rich diet, melatonin decreased TC levels and increased HDL and glucose levels, but did not change triglyceride concentrations. Our meta-analysis found no beneficial effect of increasing the dose of melatonin with fortified diets. With a standard diet, long-term melatonin therapy also reduced insulin levels, but had no effect on TC and increased glucose levels. The deterioration in carbohydrate metabolism was associated with higher doses of melatonin at the beginning of therapy, with intraperitoneal administration or with administration through a gastric tube, with administration in the light phase. In addition, high doses of melatonin have been associated with poor lipid metabolism in the standard diet. The effect of melatonin was directed towards minimizing changes in the lipid profile caused by diet, which confirms the homeostatic role of melatonin in lipid metabolism.