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Human studies

L-Carnitine

Transport biology explains cellular carnitine availability. Human supplementation findings range from small null trials to modest, variable pooled metabolic changes.

Research summary

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

Frontiers in nutrition 2022

Zamani M, Pahlavani N, Nikbaf-Shandiz M, Rasaei N, Ghaffarian-Ensaf R, Asbaghi O, Shiraseb F, Rastgoo S

Systematic review of randomised human trials

Pooled results from 41 L-carnitine trials involving 2,900 adults favoured lower fasting glucose, HbA1c and estimated insulin resistance. Results varied substantially between trials, with very high statistical heterogeneity and differences by population and study duration. The average change therefore describes a diverse supplementation literature rather than one consistent metabolic response.

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Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis.

Clinical nutrition ESPEN 2020

Talenezhad N, Mohammadi M, Ramezani-Jolfaie N, Mozaffari-Khosravi H, Salehi-Abargouei A

Systematic review of human trials

Across 37 trials involving 2,292 adults, pooled L-carnitine results showed modest reductions in body weight, BMI and fat mass, but no significant change in waist circumference or body-fat percentage. Restricting the analysis to higher-quality trials retained only the body-weight finding. Differences between populations and protocols remain important when interpreting the average result.

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Effect of oral L-carnitine administration on insulin sensitivity and lipid profile in type 2 diabetes mellitus patients.

Annals of nutrition & metabolism 2008

González-Ortiz M, Hernández-González SO, Hernández-Salazar E, Martínez-Abundis E

Small randomised placebo-controlled human trial

Insulin sensitivity and lipid profiles did not change significantly with L-carnitine in a four-week placebo-controlled trial involving 12 adults with type 2 diabetes. Only six received L-carnitine. This small null trial is a useful counterpoint to pooled results from larger, more varied supplementation literatures.

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Carnitine transport and fatty acid oxidation.

Biochimica et biophysica acta 2016

Longo N, Frigeni M, Pasquali M

Cellular and animal mechanistic research

Cellular carnitine availability depends on uptake and retention as well as biosynthesis. The OCTN2 transporter is central to this balance; defects can greatly reduce cellular accumulation and increase urinary losses. This biochemical and clinical-genetic context explains why adding carnitine and having an intact transport system are different experimental variables.

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Models studied

  • Randomised human trials
  • Glycaemic biomarkers
  • Metabolic research
  • Study-design and population differences

Key findings

  • Transport and cellular availability

    OCTN2-mediated uptake and retention help determine cellular availability alongside synthesis.

  • Human glycaemic findings and variability

    Pooled glycaemic changes varied substantially across populations and protocols rather than representing one uniform response.

  • Body-composition evidence

    Body-weight findings were more robust than several other body-composition endpoints when trial quality was considered.

  • A small insulin-sensitivity null trial

    The four-week trial found no significant insulin-sensitivity or lipid change and included only six participants receiving carnitine.

References

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

    Frontiers in nutrition 2022

    Zamani M, Pahlavani N, Nikbaf-Shandiz M, Rasaei N, Ghaffarian-Ensaf R, Asbaghi O, Shiraseb F, Rastgoo S

    PMID 36704801

    View on PubMed

  2. Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis.

    Clinical nutrition ESPEN 2020

    Talenezhad N, Mohammadi M, Ramezani-Jolfaie N, Mozaffari-Khosravi H, Salehi-Abargouei A

    PMID 32359762

    View on PubMed

  3. Effect of oral L-carnitine administration on insulin sensitivity and lipid profile in type 2 diabetes mellitus patients.

    Annals of nutrition & metabolism 2008

    González-Ortiz M, Hernández-González SO, Hernández-Salazar E, Martínez-Abundis E

    PMID 18714152

    View on PubMed

  4. Carnitine transport and fatty acid oxidation.

    Biochimica et biophysica acta 2016

    Longo N, Frigeni M, Pasquali M

    PMID 26828774

    View on PubMed

For laboratory research use only. Content is provided for research reference and is not intended as medical or veterinary guidance.