L-carnitine plays a major role in the transport of fatty acids into the interior of cells. Once inside the cell, the fatty acids are converted to energy.
Carnitine is thus of particular importance for processes with regard to energy supply and fat burning.
Healthy individuals require approx. 300 mg L-carnitine per day. This requirement can increase significantly in special situations (athletic activity, pregnancy, illness). Aging also increases demand.
The body is able to synthesize small amounts of carnitine on its own using elements such as niacin, vitamin B6, iron, and vitamin C. However, the majority (approx. 90%) must be ingested through food.
What are the functions of L-carnitine in the body?
- Transport of fatty acids (energy) into the interior of cells;
- Reduces recovery time for athletes;
- Detoxes cells, improves immune function;
- Improves glucose metabolism, therefore recommended for diabetics;
- Regulates lipid metabolism and may have positive effects on cholesterol levels;
- Is important for the development of the fetus during pregnancy and the newborn during nursing;
- Provides sperm with energy, promotes male fertility.
The name “carnitine” gives a hint as to its primary origin. It is almost exclusively found in meat (Latin: carnis). Plants contain very little carnitine. For this reason, vegetarians often evidence low levels of carnitine in their blood.
During the 1990’s, carnitine was the great hope of the diet industry: could taking L-carnitine boost fat burning?
Larger amounts of L-carnitine are only found in meat. In order for the body to synthesize its own carnitine, lysine, iron, and vitamin C are required. Foods with a high content of L-carnitine are:
- Crabs (9,000 mg per kg)
- Mutton (2,100 mg per kg)
- Goat Meat (1,700 mg per kg)
- Lamb (780 mg per kg)
- Beef (700 mg per kg)
- Pork (300 mg per kg)
Poultry only contains 80 mg per kg. A liter of milk contains approx. 25 mg L-carnitine. Plant-based foods contain significantly less than 30 mg L-carnitine per kg: rice 18 mg per kg, avocados 13 mg per kg, bread 8 mg per kg, potatoes 0.3 mg per kg.
Causes for carnitine deficiency or increased requirements include:
- Pregnancy, nursing
- Vegetarian diet
- Low levels of iron or vitamin C
- Intense athletic activity
- Infections, especially HIV
- Hypothyroidism (underactive thyroid)
- Liver or kidney function disorders
Vegetarians in particular often evidence low levels of iron, which then negatively affects carnitine production.
The body itself requires 100 mg to 300 mg per day. In nutrition medicine, dosages ranging from 500 mg to 5,000 mg daily are recommended.
Even with high doses of 5,000mg a day, no side effects are to be expected. In rare cases, some minor digestive issues may occur.
Functions and Benefits of L-carnitine
Improved fat metabolism through L-carnitine?
In the body, burning fat is a process that depends on many factors. Whether or not supplementation with L-carnitine as a transport medium for fatty acids into cells can simplify the burning of fat depends on whether or not the amount of available L-carnitine is a limiting factor.
In a study conducted in 1998, obese individuals were able to boost fat burning through supplementation with carnitine 1. According to more recent studies, often the amount of fat-splitting enzymes or the permeability of the cell membrane is the limiting factor.
Supplementation with L-carnitine can lead to increased fat burning only in cases where there is a limited availability of carnitine in the body. For people who rarely exercise, L-carnitine will presumably not provide any increase in fat burning. However, for active individuals, taking carnitine may promote fat metabolism 2.
L-carnitine for shorter recovery time following athletic activity
As a receptor molecule, L-carnitine is necessary to channel activated fatty acids from the cytoplasm through the membrane of the mitochondrion. Inside the mitochondrion the fatty acids are converted into energy.
It is presumed that carnitine also transports lactic acid and thereby protects the power generators of cells (the mitochondria) from acidosis.
Several studies have shown that after endurance activities, recovery time can be reduced through L-carnitine.
Additionally, it has been observed that after an intense muscle workout like weightlifting, muscle soreness can be decreased by taking L-carnitine.
L-carnitine for sperm health
Carnitine may increase motility of sperm in men. Sperm require a great deal of energy that is supplied by long-chained fatty acids. These fatty acids have to be brought into the interior of cells via carnitine to be converted into energy. It appears that carnitine availability may be a limiting factor in the energy generation capabilities of sperm.
Several studies consistently proved that the number of healthy, motile sperm in men with oligozoopermia (low number of sperm) or asthenozoospermia (reduced motility of sperm in ejaculate) could be significantly increased by taking L-carnitine. Study participants took L-carnitine for a time period of three to six months 3, 4, 5.
Pregnancy and Nursing
Women who are pregnant or nursing evidence a higher requirement of L-carnitine. This is why pregnant women often have a lower blood level of carnitine than their non-pregnant counterparts.
Both the blood of the umbilical cord and breast milk contain high concentrations of L-carnitine. This highlights the importance of L-carnitine in early childhood development. Supplementation with L-carnitine during pregnancy may lead to improved weight gain and development of the newborn.
Since vitamin C and iron are important for carnitine synthesis, carnitine availability can be improved by taking supplemental vitamin C and iron.
Carnitine can help lower cholesterol
Carnitine has been shown to have positive effects on triglyceride metabolism. In one study, participants received 900 mg L-carnitine a day over a period of 8 weeks. Results showed a significant decrease in cholesterol levels 6.
In another study in which patients with lipid metabolism disorders were given 3,000 mg L-carnitine a day for six weeks, cholesterol values were also improved 7. Triglyceride levels in the blood were reduced and the ratio of HDL cholesterol to total cholesterol was improved. Additionally a study conducted in 1982 recorded higher HDL (good cholesterol) levels in participants who received L-carnitine supplementation and a reduction in serum triglycerides 8.
Lowering blood sugar levels
In a study conducted on patients with diabetes mellitus, L-carnitine supplementation significantly improved sugar metabolism. Insulin resistance decreased and blood sugar was better utilized 9. Even the typically high levels of blood lipids (triglycerides and ketone bodies) often associated with diabetes were lowered in study participants through L-carnitine.
- Lutz R, Fischer R. Carnitine for weight loss support in obesity. Magazine for Natural Healing Processes. 1998. 39(1):12-15 ↩
- Arndt K, Albers T. Manual Protein and Amino Acids. 2004. 2nd Edition. 263. ↩
- Costa M, Canale D, Filicori M, D’Iddio S, Lenzi A. L- carnitine in idiopathic asthenozoospermia: a multicenter study. Italian Study Group on Carnitine and Male Infertility. Andrologia. 1994. 26:155-159 ↩
- Lenzi A, Lombardo F, Sgro P, Salacone P, Caponecchia L, Dondero F, Gandini L. Use of carnitine therapy in selected cases of male factor infertility: a double-blind crossover trial. Fertility and Sterility. 2003. 79:292-300 ↩
- Balercia G, Regoli F, Armeni T, Koverech A, Mantero F, Boscaro M. Placebo-controlled double-blind randomized trial on the use of L-carnitine, L-acetylcarnitine, or combined L-carnitine and L-acetylcarnitine in men with idiopathic asthenozoospermia. Fertility and Sterility. 2005. 84(3):662-71 ↩
- Maebashi M, Kawamura N, Sato M, Imamura A, Yoshinaga K. Lipid lowering effect of carnitine in patients with type IV hyperliproteinemia. The Lancet. 1978. 2(8094): 805-807 ↩
- Pola P, Savi L, Grilli M. Carnitine in the therapy of dyslipidemic patients. Curr Ther Res. 1980. 27: 763-764 ↩
- Rossi CS, Siliprandi N. Effect of carnitine on serum HDL-cholesterol: report of two cases. John Hopkins Medical Journal. 1982. 150(2):51-54 ↩
- Giancaterini A, De Gaetano A, Mingrone G, Gniuli D, Liverani E, Capristo E, Greco AV. Acetyl-l-Carnitine infusion increases glucose disposal in type 2 diabetic patients. Metabolism. 2000. 49(6):704-708 ↩