AUTHOR=Zamani Mohammad , Pahlavani Naseh , Nikbaf-Shandiz Mahlagha , Rasaei Niloufar , Ghaffarian-Ensaf Rasool , Asbaghi Omid , Shiraseb Farideh , Rastgoo Samira 

TITLE=The effects of L-carnitine supplementation on glycemic markers in adults: A systematic review and dose-response meta-analysis

JOURNAL=Frontiers in Nutrition

VOLUME=9

YEAR=2023

URL=https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2022.1082097

DOI=10.3389/fnut.2022.1082097

ISSN=2296-861X

ABSTRACT=<sec><title>Background and aims</title><p>Hyperglycemia and insulin resistance are concerns today worldwide. Recently, L-carnitine supplementation has been suggested as an effective adjunctive therapy in glycemic control. Therefore, it seems important to investigate its effect on glycemic markers.</p></sec><sec><title>Methods</title><p>PubMed, Scopus, Web of Science, and the Cochrane databases were searched in October 2022 for prospective studies on the effects of L-carnitine supplementation on glycemic markers. Inclusion criteria included adult participants and taking oral L-carnitine supplements for at least seven days. The pooled weighted mean difference (WMD) was calculated using a random-effects model.</p></sec><sec><title>Results</title><p>We included the 41 randomized controlled trials (RCTs) (<italic>n</italic> = 2900) with 44 effect sizes in this study. In the pooled analysis; L-carnitine supplementation had a significant effect on fasting blood glucose (FBG) (mg/dl) [WMD = −3.22 mg/dl; 95% CI, −5.21 to −1.23; <italic>p</italic> = 0.002; <italic>I</italic><sup>2</sup> = 88.6%, <italic>p</italic> &lt; 0.001], hemoglobin A1c (HbA1c) (%) [WMD = −0.27%; 95% CI, −0.47 to −0.07; <italic>p</italic> = 0.007; <italic>I</italic><sup>2</sup> = 90.1%, <italic>p</italic> &lt; 0.001] and homeostasis model assessment-estimate insulin resistance (HOMA-IR) [WMD = −0.73; 95% CI, −1.21 to −0.25; <italic>p</italic> = 0.003; <italic>I</italic><sup>2</sup> = 98.2%, <italic>p</italic> &lt; 0.001] in the intervention compared to the control group. L-carnitine supplementation had a reducing effect on baseline FBG ≥100 mg/dl, trial duration ≥12 weeks, intervention dose ≥2 g/day, participants with overweight and obesity (baseline BMI 25–29.9 and &gt;30 kg/m<sup>2</sup>), and diabetic patients. Also, L-carnitine significantly affected insulin (pmol/l), HOMA-IR (%), and HbA1c (%) in trial duration ≥12 weeks, intervention dose ≥2 g/day, and participants with obesity (baseline BMI &gt;30 kg/m<sup>2</sup>). It also had a reducing effect on HOMA-IR in diabetic patients, non-diabetic patients, and just diabetic patients for insulin, and HbA1c. There was a significant nonlinear relationship between the duration of intervention and changes in FBG, HbA1c, and HOMA-IR. In addition, there was a significant nonlinear relationship between dose (≥2 g/day) and changes in insulin, as well as a significant linear relationship between the duration (weeks) (coefficients = −16.45, <italic>p</italic> = 0.004) of intervention and changes in HbA1C.</p></sec><sec><title>Conclusions</title><p>L-carnitine could reduce the levels of FBG, HbA1c, and HOMA-IR.</p></sec><sec><title>Systematic review registration</title><p><ext-link ext-link-type="uri" xlink:href="https://www.crd.york.ac.uk/prospero/" xmlns:xlink="http://www.w3.org/1999/xlink">https://www.crd.york.ac.uk/prospero/</ext-link>, identifier: CRD42022358692.</p></sec>