L-Carnitine’s Effect on the Biomarkers of Metabolic Syndrome: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Abstract

A systematic review and meta-analysis of randomized controlled trials (RCTs) was carried out to assess L-carnitine supplements’ influence on the biomarkers of metabolic syndrome (MetSyn). PubMed, EMBASE, Cochrane library, and CINAHL were used to collect RCT studies published prior to February 2020. RCT studies were included if they had at least one of the following biomarker outcome measurements: waist circumference (WC), blood pressure (BP), fasting blood sugar (FBS), triglyceride (TG), or high density lipoprotein-cholesterol (HDLc). Nine of twenty studies with adequate methodological quality were included in this meta-analysis. The dose of L-carnitine supplementation administered varied between 0.75 and 3 g/day for durations of 8–24 weeks. L-carnitine supplementation significantly reduced WC and systolic BP (SBP), with no significant effects on FBS, TG, and HDLc. We found that L-carnitine supplementation at a dose of more than 1 g/d significantly reduced FBS and TG and increased HDLc. In conclusion, L-carnitine supplementation is correlated with a significant reduction of WC and BP. A dose of 1–3 g/d could improve the biomarkers of MetSyn by reducing FBS and TG and increasing HDLc.

Effects of l-carnitine supplementation on glucolipid metabolism: a systematic review and meta-analysis

“…This suggests that 6 months of use is a critical juncture and that physicians should ensure a duration of administration of at least six months when applying l -carnitine for glucose control improvement. Interestingly, we also found that l -carnitine supplement could effectively reduce FBG in people who are overweight without being obese (24 < BMI ≤ 28), which was not in accordance with Choi et al 32 A possible explanation is that the current work was performed without restrictions in specific disease or intervention, as well as included more RCTs comparing to Choi et al The physiological roles of l -carnitine may also help to explain that l -carnitine is primarily responsible for maintaining β-oxidation and overall energy balance of the body; 30,35 thus, l -carnitine supplementation is more likely to be effective when the energy balance is disturbed, such as when overweight. In addition, our previous studies also found that changes in the oxygen environment of the body only affected skeletal muscle l -carnitine redistribution in overweight mice but not in control animals.…”

“…Interestingly, we also found that L-carnitine supplement could effectively reduce FBG in people who are overweight without being obese (24 < Abbreviations: MD: mean differences, CI: confidence interval, FBG: fasting blood glucose, TG: triglycerides, TC: total cholesterols, LDLc: low−density lipoprotein-cholesterol, HDLc: high-density lipoprotein-cholesterol, BMI: body mass index, RCT: randomized controlled trial, DM: diabetes mellitus. Food & Function Paper BMI ≤ 28), which was not in accordance with Choi et al 32 A possible explanation is that the current work was performed without restrictions in specific disease or intervention, as well as included more RCTs comparing to Choi et al The physio-logical roles of L-carnitine may also help to explain that L-carnitine is primarily responsible for maintaining β-oxidation and overall energy balance of the body; 30,35 thus, L-carnitine supplementation is more likely to be effective when…”

“…30,31 However, recent development in this topic resulted in controversies. In 2020, a meta-analysis reported that L-carnitine supplementation had no significant effects on the reduction of FBG 32 in the initial analysis. However, after expanding the sample size to include more RCTs and different interventions, this work showed that L-carnitine intervention indeed had significant effects on reducing FBG, insulin levels, and HOMA-IR, confirming the importance of extensive inclusion of RCTs.…”

“…Two meta-analysis studies reported that l -carnitine supplementation reduced fasting blood glucose (FBG) 16 and triglyceride (TG), 17 while Choi et al concluded that it was ineffective on these parameters on patients with metabolic syndrome. 18 l -Carnitine was ineffective in reducing total cholesterol (TC) levels in the meta-analysis performed by Mohammad et al , while recently, Jung et al 19 reported that l -carnitine significantly decreased cholesterol concentrations in patients with hepatic steatosis. Previous meta-analyses also reported that l -carnitine could alleviate HOMA-IR in patients with type 2 diabetes mellitus (DM) or nonalcoholic fatty liver disease.…”

The Effect of Walnut (Juglans regia) Leaf Extract on Glycemic Control and Lipid Profile in Patients With Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

“…Subgroup analysis was performed to examine probable sources of heterogeneity, according to predefined variables including dosage (≤ 200 vs. > 200 mg/day) and duration (≤ 8 vs. > 8 weeks). For studies with missing values of SD for mean difference, the following formula was used: SD = square root ((SD pretreatment ) 2 + (SD posttreatment ) 2 − (2R × SD pretreatment × SD posttreatment )), where correlation coefficient (R) was assumed equal to 0.5 [ 26 ]. Effect sizes were expressed as the mean difference and 95% confidence interval (CI).…”