Carnitine is an amino acid that is synthesized in the liver and kidneys from lysine and methionine. Its major biochemical function is to facilitate the transport and metabolism of long-chain fatty acids into the mitochondria for beta-oxidation and energy generation.
There is extensive research on carnitine, as seen in the following research overview. The focus is on athletic performance and enhanced endurance; increased fat metabolism; lowering of cholesterol and triglyceride levels; and heart protection. Because carnitine facilitates fatty acid transport into the mitochondria for oxidation, researchers initially theorized that it is possible that elevated carnitine levels would permit a greater/faster transport of fat leading to increased fat oxidation, which may impact weight loss and/or endurance performance. When the body relies on fat for energy this could result in sparing of muscle glycogen and a subsequent enhancement of exercise performance. Researchers also theorized that supplemental carnitine could help to reduce lactic acid accumulation in muscles by buffering pyruvate and, therefore, enhance endurance.
Exercise and endurance studies are ongoing and researchers express difficulty in measuring results. However, unequivocal results in kidney dialysis patients show that low carnitine levels in the dialysate can lead to elevated levels of blood lipids. Similarly, studies of heart disease patients have shown that carnitine supplements (2g/ day over 6 months) can reduce cholesterol and triglyceride levels. In one important study among patients who suffered a heart attack, carnitine supplements (2-3 g/day over 4-8 weeks) resulted in a reduction in the amount of damage to the heart muscle and an increase in heart muscle viability. In angina sufferers, carnitine reduces the incidence of angina and cardiac arrhythmias as well as reduces the need for anti-angina and anti-arrhythmic medications. In addition, carnitine (2g/ day for 6 months) can also increase exercise tolerance in patients with angina – meaning that they can exercise longer and at a higher level before experiencing chest pain.
Dietary Sources: meat and dairy products.
Daily Reference Intake: There is no DRI or RDA for carnitine.
Side Effects: Carnitine supplementation has an excellent safety record. Doses of 2-6 grams per day over a period of 6 months have been studied with no observed adverse side effects. The D-Carnitine, inactive form is not recommended.
Acetyl-L-carnitine research shows the following:
1. Treats age-related macular degeneration (HUMAN)
2. Reduces metabolic abnormalities induced by alcohol (ANIMAL)
3. Reverses biochemical and behavioral parameters of brain aging
4. Maintains myocardial function (ANIMAL)
5. Ameliorates oxidative damage, enzyme activity, substrate-binding affinity, and mitochondrial dysfunction (ANIMAL)
6. Improves metabolic function while decreasing oxidative stress (ANIMAL)
7. Normalizes age-dependent disturbances such as membrane lipid metabolism and/or composition (ANIMAL)
8. Reduces age-associated deterioration in auditory sensitivity and improves cochlear function (ANIMAL)
9. Reverses the age-related decrement in the mitochondrial pyruvate metabolism (ANIMAL)
10. Benefits various cognitive functions in the middle-aged and elderly and is a metabolic cofactor (REVIEW-HUMAN)
11. Has a beneficial effect on the neuromuscular junction and on muscle fiber structure in ageing or after nerve crushing (ANIMAL)
12. Reverses age-related decrement in mitochondrial carnitine-acylcarnitine exchange activity (ANIMAL)
13. Enhances spatial acquisition in of rats with age-related behavioral impairments in a novel environment (ANIMAL) Two Studies.
14. Has positive effects on the brain NMDA receptor system (ANIMAL)
15. Theoretically useful in Alzheimer's (REVIEW) (ANIMAL)
16. Preserves, at least partially, learning and memory from the natural decay occurring with age (ANIMAL)
17. Has a neurotrophic action on the peripheral nervous system with possible applications in age-related peripheral nerve changes (ANIMAL)
18. Has a positive effect on age-related changes in the dopaminergic system (ANIMAL)
19. Rescues aged neurons may be by increasing their responsiveness to neuronotrophic factors in the CNS (ANIMAL)
20. Shows improvements in spatial memory (ANIMAL)
21. Acetyl-L-carnitine is a precursor of acetylcholine.
22. Attenuates certain age-related cognitive deficits and may have a beneficial effect on longevity (ANIMAL)
23. Being investigated as a determinant of neuronal longevity
24. Reduces the age-dependent loss of glucocorticoid receptors in the hippocampus (ANIMAL)
25. Mainly affects the inner membrane protein composition of cerebellar mitochondria (ANIMAL)
26. Improves cognitive performance, ameliorates age-related deficits (ANIMAL)
27. May be the first agent suitable for clinical use in the prevention of neuronal death after peripheral nerve trauma (ANIMAL)
28. May assist treatment of peripheral neuropathy in patients on antiretroviral therapy
29. Positively affects spatial memory and nerve growth factor levels (ANIMAL)
30. Rescues neurons from beta 25-35-induced neurotoxicity (ANIMAL)
31. Exerts a neuroprotective effect and decreases stress exposure in the CNS (ANIMAL)
32. May have a role in counteracting degenerative disease
33. Restores choline acetyltransferase activity in the hippocampus (ANIMAL)
34. Considered useful as a therapeutic agent in neurodegenerative disorders (ANIMAL)
35. Significantly elevated beta-NGF (nerve growth factor) (ANIMAL)
36. Has neurotrophic properties (ANIMAL)
37. Restores choline acetyltransferase activity (ANIMAL)
38. Important in the development of therapeutic strategies to counteract degenerative diseases of the CNS
39. Abolished the age-associated reduction of a specific mRNA levels in the basal forebrain of old animals (ANIMAL)
40. Compared to Alzheimer's patients on placebo, acetyl-L-carnitine-treated patients showed significantly less deterioration in their Mini-Mental Status and Alzheimer's Disease Assessment Scale test scores. (HUMAN)
41. Has a neuroprotective effect
42. Suggests a neurotrophic property exerted on those central cholinergic pathways typically damaged by aging (ANIMAL)
43. Long-term treatment completely prevents the loss of choline acetyltransferase activity in the CNS of aged rats (ANIMAL)
44. Preserves and/or facilitates the functionality of carnitines, the concentrations of which are diminished in the brain of old animals (ANIMAL)
45. Stimulates nerve growth factor receptors (ANIMAL)
46. Doubled the number of aged neurons treated compared to controls (ANIMAL)
47. Rescues aged neurons by increasing their responsiveness to neuronotrophic factors in the CNS (ANIMAL)
48. Increases choline acetyltransferase activity and of nerve growth factor receptor expression in the striatum (ANIMAL)
49. Chronic treatment prevents some age-related impairments of CNS (ANIMAL)
50. Improves cognitive performance of aged rats, ameliorates these age-related deficits.
51.-62. Human Research on Down Syndrome, Alzheimer's, dementia. 11 Citations
Acetyl-L-Carnitine Abstracts (50)
Acetyl-L-Carnitine Citations (11)