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Carnitine, SLC22A5, and What Your Genotype Means for Energy and Muscle Health

Carnitine is a small but essential molecule that helps transport long-chain fatty acids into mitochondria, the cell’s power plants, where they are burned for energy. It also plays a role in removing metabolic waste and supporting steady energy supply in tissues that use a lot of fuel, especially heart and skeletal muscle. The SLC22A5 gene encodes the OCTN2 transporter responsible for moving carnitine into cells and conserving carnitine in the kidneys. Variations in SLC22A5 can change how efficiently cells take up and retain carnitine, which can affect energy, recovery, and tolerance to metabolic stress.

How genetic differences can affect you

  • Reduced transporter function may lower cellular carnitine availability, especially during times of increased demand such as illness, pregnancy, calorie restriction, or intense exercise.
  • Symptoms that can arise when carnitine is low include unexplained fatigue, exercise intolerance, muscle cramps, and in more severe cases, problems with heart or liver function.
  • Most people who carry one altered copy do not develop a disorder, but two altered copies are associated with primary carnitine deficiency and higher risk of symptomatic issues.

Everyday steps to support carnitine and mitochondrial energy

  • Diet: Include quality protein sources rich in lysine and methionine, the amino acid building blocks for carnitine. Examples: fish, poultry, lean red meat, eggs, dairy, legumes, and soy products.
  • Food sources of carnitine: Red meat and dairy contain the highest dietary carnitine; fish and poultry have moderate amounts.
  • Micronutrients: Ensure adequate vitamin C, vitamin B6, vitamin B12, iron, and niacin to support carnitine synthesis and mitochondrial function. Aim for a balanced diet or discuss targeted testing and supplementation with your clinician.
  • Exercise: Regular aerobic training and resistance exercise stimulate mitochondrial capacity and improve fatty acid use. Gradual progression and proper recovery are key.
  • Sleep and stress: Prioritize 7 to 9 hours of quality sleep and use stress-management strategies such as mindfulness, paced breathing, or moderate activity to reduce metabolic strain.
  • Hydration and recovery: Maintain good hydration and structured recovery periods around intense training or illness.
  • Monitoring: Track energy levels, exercise tolerance, and recovery. If you notice persistent or worsening symptoms, seek clinical evaluation and testing of carnitine status.

Supplements and clinical considerations

Some people may benefit from supplements such as L-carnitine or coenzyme Q10 to support mitochondrial energy, particularly if testing shows low carnitine or if symptoms suggest impaired fatty acid oxidation. Supplementation should be considered under medical supervision because dosing, interactions, and monitoring vary by individual. A healthcare provider can order blood tests to measure free and total carnitine, and evaluate whether supplementation is appropriate.

PlexusDx does not provide medical advice. This information is educational only. Always discuss genetic results, testing, treatment, and supplementation with your healthcare provider before making changes.

Genetic interpretations

Two effect alleles (GG) — increased likelihood of impacted carnitine transport

If your genotype at rs72552725 is GG, you carry two copies of the effect allele associated with reduced OCTN2 transporter activity. This pattern is linked to primary carnitine deficiency and may reduce how efficiently cells import and conserve carnitine, especially during metabolic stress.

What this can mean for you

  • Higher risk of low cellular carnitine under stressors such as illness, prolonged fasting, pregnancy, or intense training.
  • Possible symptoms include unexplained fatigue, poor exercise tolerance, muscle weakness or cramps, and slower recovery.
  • In severe cases, cardiac and liver function can be affected; however many individuals remain asymptomatic without additional stressors.

Practical recommendations

  • Discuss carnitine testing with your healthcare provider, including plasma free and total carnitine levels and any needed metabolic workup.
  • Prioritize dietary sources of carnitine and the amino acids lysine and methionine: include red meat, fish, dairy, poultry, eggs, legumes, and soy.
  • Ensure adequate intake of vitamin C, B6, B12, iron, and niacin through diet or under clinician guidance via supplements if deficiencies are present.
  • Consider supervised L-carnitine supplementation if tests or clinical symptoms indicate deficiency. Use clinical monitoring for response and safety.
  • Adopt a consistent exercise plan emphasizing both aerobic and resistance work, with careful pacing and recovery strategies.
  • Monitor energy, exercise tolerance, and any new muscle or cardiac symptoms; seek medical attention if symptoms worsen.
One effect allele (AG) — carrier status with potential stress-related impact

If your genotype is AG, you are a carrier of a mutation in SLC22A5. Most carriers do not develop full-blown primary carnitine deficiency, but the single altered copy can make carnitine transport slightly less efficient during times of high demand.

What this can mean for you

  • Usually no symptoms at baseline, but possible reduced reserve during illness, prolonged low-calorie diets, pregnancy, or very intense training.
  • Pay attention to unexpected fatigue, slower recovery, or new exercise intolerance that emerges during stress.

Practical recommendations

  • Follow a diet providing adequate protein with lysine and methionine: fish, poultry, lean meats, eggs, dairy, legumes, and tofu.
  • Include carnitine-containing foods—moderate amounts from fish and poultry, higher from red meat and dairy—balanced within your dietary preferences and needs.
  • Support nutrient status for carnitine synthesis: vitamin C, B6, B12, iron, and niacin.
  • Consider carnitine testing if you experience unexplained fatigue, muscle symptoms, or poor recovery; discuss targeted supplementation like L-carnitine or coenzyme Q10 with your clinician if indicated.
  • Maintain regular aerobic and resistance training, prioritize sleep, and manage stress to protect mitochondrial function.
No effect alleles (AA) — typical SLC22A5 function

If your genotype is AA, you carry two copies of the non-effect allele and your OCTN2 transporter is expected to function typically. This supports normal cellular uptake and renal conservation of carnitine under most conditions.

What this can mean for you

  • Normal carnitine transport and typical cellular energy handling at baseline.
  • Standard attention to diet, exercise, sleep, and micronutrients is usually sufficient to maintain healthy carnitine status.

Practical recommendations

  • Consume adequate protein and carnitine-containing foods as part of a balanced diet.
  • Ensure sufficient vitamin C, B6, B12, iron, and niacin either from diet or under healthcare advice.
  • Engage in regular aerobic and resistance exercise, maintain good sleep hygiene, stay hydrated, and manage stress.
  • Seek evaluation only if unexpected symptoms such as persistent fatigue or muscle issues arise.

PlexusDx does not provide medical advice. This information is for education about genetic predispositions only. Always consult your healthcare provider to interpret genetic results, order relevant tests, and decide on any supplementation or treatment.