Carnitine is present in almost every cell of the body. It is conditionally an essential nutrient. It occurs in two-forms, D and L.
L-carnitine is the biologically active form found in body, foods, and supplements.
Table 1:-Selected Food Sources of Carnitine
|
Food |
Amount (Mg) |
|
Beef, cooked (4 ounces) |
56-162 |
|
Milk, whole, 1cup |
8 |
|
Chicken (4ounce) |
3-5 |
|
Cheddar cheese (2 ounce) |
2 |
When can carnitine deficiency occur?
The body is designed to make sufficient carnitine to meet the required needs. But incase of genetic or medical condition some individuals cannot make enough carnitine, so for them, carnitine becomes a conditionally essential nutrient.
-
Primary Carnitine Deficiency
The genetic mutation of cellular carnitine transport system with symptoms of skeletal muscle weakness, cardiomyopathy. It doesn’t lead to the absorption of Carnitine.
- Secondary Carnitine Deficiency
This can occur due to chronic kidney diseases, certain antibiotics may reduce carnitine absorption or increase its excretion.
Carnitine has two functions:-
1) Canitine Stimulates Utilisation Of Carbohydrate and Amino acids:-
Common metabolite in the oxidation of fattyacids, amino acids, glucose is acetyl CoA, Carnitine transports it as acetylcarnitine across the mitochondrial membrane.
2) Fatty Acid Metabolism and Energy Production:-
A part of carnitine transports long-chain fatty acids into the mitochondria. They are burned or oxidised, to produce energy.
3) Removal of Toxins:-
Another part transports waste and toxic compounds out of the mitochondria, and this prevents unwanted substances from building up.
Skeletal and cardiac muscles use fatty acids as a dietary fuel to have high concentrations of carnitine.
Carnitine - biosynthesis, absorption and metabolism
L-carnitine is absorbed from foods via both active and passive transport across enterocyte (intestinal cell) membranes and then enters the blood stream.
Carnitine not obtained from food is synthesised endogenously from two essential amino acids, lysine and methionine. This occurs in the kidney, liver and brain.
Ascorbic acid, ferrous iron, pyroxidine maybe few necessary cofactors.(Rebouche CJ, 1990)
The kidneys can efficiently conserve carnitine, so even carnitine-poor vegetarian diets have little impact on the body’s total carnitine content
Rather than being metabolised, excess carnitine is excreted in the urine, to maintain stable blood concentrations. (Stanley, et al,2004)
There are three different forms of carnitine:
- L-carnitine
- Acetyl-L-carnitine (ALCAR)
- Propionyl-L-carnitine
Experimental evidence suggests that the transport of long-chain fatty acids into the mitochondria is a rate-limiting step in fatty acid oxidation.
During sustained low to moderate exercise, fatty acid oxidation increases to become the predominant energy source to muscles.
Table -2 Different forms of L-Carnitine supplements
|
L- Carnitine (Tartrate) |
Acetyl L-carnitine |
Propionyl-L-Carnitine |
|
Most effective form for mobilisation and oxidation of deposited fat stores. |
Most effective form for your brain. Helps boost brain energy and focus |
Most effective form for clinical use, such as peripheral vascular disease, high blood pressure. |
|
It transports fatty acids to the mitochondria of cells (where energy is produced) to be burned off and used for energy to fuel the body. It also maximises your fat loss potential. |
It easily passes the blood brain barrier, helps promote synthesis of a primary neurotransmitter “acetylcholine” Acetyl-L-carnitine participates in both anabolic and catabolic pathways in cellular metabolism |
It easily passes the blood-brain barrier, helps promote the synthesis of a primary neurotransmitter “acetylcholine” Acetyl-L-carnitine participates in both anabolic and catabolic pathways in cellular metabolism |
|
It may aid Muscle Soreness and recovery Stamina in exercise/ sports performance. (J.Arenas et al. (1994) |
Acetylcholine improves communication between nerve cells. Beneficial effects on brain function in various diseases such as Alzheimer’s disease. |
It may help heart patients with angina (chest pain), Important for heart function. |
L- Carnitine and Athletic Performance
Some athletes take carnitine to improve performance. However, there is no consistent evidence on whether that helps increase the body’s use of oxygen, improve metabolic status or amount of carnitine in muscles. (Brass EP, 2000).
It may prevent the accumulation of lactic acid. L-Carnitine:L-Tartrate form in the ratio - 2:1 may be generally used in sports supplements.
Although, good at promoting the mobilisation of fat from storage deposits to be burned as energy as well as boosting body-building workouts or athletic performances.
Hence, Carnitine plays an important role in fat oxidation, certain clinical issues and maybe in enhancing exercising muscle performance.
References
- Rebouche CJ. Carnitine. In: Modern Nutrition in Health and Disease, 9th Edition (edited by Shils ME, Olson JA, Shike M, Ross, AC).
- Lippincott Williams and Wilkins, New York, 1999, pp. 505-12.
- Stanley CA. Carnitine deficiency disorders in children. Ann NY Acad Sci 2004;1033:42-51. [PubMed abstract]
- Brass EP. Supplemental carnitine and exercise. Am J Clin Nutr 2000;72:618S-23S. [PubMed abstract]
- The editors. Carnitine: lessons from one hundred years of research. Ann NY Acad Sci 2004;1033:ix-xi.ods.od.nih.gov. Carnitine. National Institute of Health Office of Dietary Supplements.
- J Arenas et al. 1994.Effects of L-carnitine on the pyruvate dehydrogenase complex and carnitine palmitoyl transferase activities in muscle of endurance athletes.PMID: 8137928
- MA. Giamberardino et al. 1996. Int J Sports Med. 1996 Jul;17(5):320-4. Effects of prolonged L-carnitine administration on delayed muscle pain and CK release after eccentric effort.