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

  • 2023-01-10
  • Frontiers in nutrition 9
    • Mohammad Zamani
    • Naseh Pahlavani
    • Mahlagha Nikbaf-Shandiz
    • Niloufar Rasaei
    • Rasool Ghaffarian-Ensaf
    • Omid Asbaghi
    • Farideh Shiraseb
    • Samira Rastgoo

Study Design

Type
Systematic Review
Population
adult participants (n = 2900) from 41 randomized controlled trials
Methods
Systematic review and meta-analysis of RCTs; searched PubMed, Scopus, Web of Science, and Cochrane in October 2022; random-effects model

Background and aims

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.

Methods

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.

Results

We included the 41 randomized controlled trials (RCTs) (n = 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; p = 0.002; I2 = 88.6%, p < 0.001], hemoglobin A1c (HbA1c) (%) [WMD = -0.27%; 95% CI, -0.47 to -0.07; p = 0.007; I2 = 90.1%, p < 0.001] and homeostasis model assessment-estimate insulin resistance (HOMA-IR) [WMD = -0.73; 95% CI, -1.21 to -0.25; p = 0.003; I2 = 98.2%, p < 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 >30 kg/m2), 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 >30 kg/m2). 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, p = 0.004) of intervention and changes in HbA1C.

Conclusions

L-carnitine could reduce the levels of FBG, HbA1c, and HOMA-IR.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier: CRD42022358692.

Research Insights

  • L-Carnitine→Reduced Fasting Blood Glucose Levels

    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; p = 0.002]

    Effect
    Beneficial
    Effect size
    Small
    Dose
    ≥2 g/day
  • L-Carnitine→Reduced HOMA-IR

    L-carnitine supplementation had a significant effect on ... homeostasis model assessment-estimate insulin resistance (HOMA-IR) [WMD = -0.73; 95% CI, -1.21 to -0.25; p = 0.003]

    Effect
    Beneficial
    Effect size
    Small
    Dose
    ≥2 g/day
  • L-Carnitine→Reduced Hemoglobin A1c

    L-carnitine supplementation had a significant effect on ... hemoglobin A1c (HbA1c) (%) [WMD = -0.27%; 95% CI, -0.47 to -0.07; p = 0.007]

    Effect
    Beneficial
    Effect size
    Small
    Dose
    ≥2 g/day
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