L-Carnitine

Your intake

What each level of l-carnitine does

Approximate dose-response bands. Individual response varies — these are starting points, not prescriptions.

1. Severely lowYOU ARE HERE

   0 mg – 330 mg

   Well below target. Risk of deficiency symptoms tied to fat oxidation.

2. Insufficient

   330 mg – 1000 mg

   Below the recommended daily target. Long-term adequacy not assured.

3. Adequate

   1000 mg – 1500 mg

   Daily target met. Standard nutritional support for fat oxidation.

4. Therapeutic

   1500 mg – 2000 mg

   Common for specific health goals. Check the evidence for your situation before sustaining this level.

5. Diminishing returns

   2000 mg – +

   Past the point where extra intake typically helps. Evidence for further benefit is thin.

Overview

Synthesised from lysine and methionine; required to shuttle long-chain fatty acids across the inner mitochondrial membrane for beta-oxidation. Adequate in unrestricted omnivorous diets; vegan/vegetarian intake is much lower but synthesis usually compensates. Therapeutic interest in cognition, neuropathy, and male fertility.

Functions

• ●Carries long-chain fatty acyl-CoA into mitochondria (CPT-1/CPT-2 cycle)
• ●Buffers acetyl-CoA pool (acetylcarnitine ↔ acetyl-CoA)
• ●Modulates membrane phospholipid turnover
• ●Antioxidant role in mitochondrial matrix

Mechanism

CPT-1 on the outer mitochondrial membrane swaps CoA for carnitine on long-chain fatty acyl-CoA; the resulting acylcarnitine crosses into the matrix where CPT-2 swaps back to acyl-CoA for beta-oxidation. Without adequate carnitine, long-chain fatty acids accumulate in cytoplasm and ATP production from fat falls — explaining the muscle weakness and cardiomyopathy of inherited carnitine deficiency.

Benefits

• ●Treatment of primary and secondary carnitine deficiency
• ●Improves angina symptoms and exercise tolerance in stable CAD
• ●Modestly improves sperm parameters in male infertility
• ●Acetyl-L-carnitine: mild benefit in diabetic neuropathy, possibly in early dementia
• ●Marketing for fat loss is largely unsupported in non-deficient adults

Deficiency

Primary deficiency is rare (transporter defect). Secondary deficiency from valproate therapy, hemodialysis, severe malnutrition, or strict vegan diet over long periods.

Excess

Generally well-tolerated. High doses can produce 'fishy odour' (TMAO metabolite). TMAO controversy: gut bacteria convert carnitine to TMAO, hypothesised CV-risk linkage — clinical relevance still debated.

Forms

• L-carnitine tartrate (LCLT)
  Standard exercise/recovery form
• L-carnitine fumarate
  Common multivitamin form
• Acetyl-L-carnitine (ALCAR)
  Crosses BBB; cognitive and neuropathy uses
• Propionyl-L-carnitine
  CV indications; peripheral artery disease trials
• L-carnitine liquid / injection
  Clinical deficiency treatment

Food sources

• Beef (cooked) · 3 oz85 mg
• Pork (cooked) · 3 oz25 mg
• Cod (cooked) · 3 oz5 mg
• Whole milk · 1 cup8 mg
• Chicken breast (cooked) · 3 oz3 mg

Supplement forms

L-carnitine tartrate (gym/recovery), L-carnitine fumarate, or acetyl-L-carnitine (cognition and neuropathy). 500–2,000 mg/day in divided doses. Take on empty stomach for absorption.

Bioavailability

Oral L-carnitine: ~15% bioavailable (active transport saturates quickly). Pharmacologic doses depend more on passive diffusion. Acetyl-L-carnitine has slightly better gut absorption and crosses BBB more readily. Carbohydrate co-ingestion increases muscle carnitine uptake (insulin-mediated).

Longevity relevance

Mitochondrial function is central to aging biology; carnitine supports fat oxidation and acetyl-CoA buffering. Direct longevity evidence in humans is thin; the TMAO question keeps the long-term supplementation case unresolved.

Relationships

References

• NIH ODS — Carnitineguideline
• Examine — Carnitinereview
• Koeth — carnitine, gut microbiota, TMAO (Nat Med 2013)study

About L-Carnitine

Fatty-acid transport into mitochondria; energy metabolism. Common dose 500–2000 mg.

Role

Fat oxidation

Daily target

1000 mg (TR)

Also called

l-carnitine, carnitine, acetyl-l-carnitine, alcar, acetyl l-carnitine