L-Carnitine is a compound that is synthesized in the body from lysine and methionine; it is found in meat products and is available as a supplement. It plays a crucial role in transporting long-chain fatty acids into the mitochondria for energy production and can be converted into acetyl-L-carnitine, which more effectively crosses the blood-brain barrier.
What is L-carnitine?
L-Carnitine is a compound that is synthesized in the body from lysine and methionine; it is found in meat products and is available as a supplement. It plays a crucial role in transporting long-chain fatty acids into the mitochondria for energy production and can be converted into acetyl-L-carnitine, which more effectively crosses the blood-brain barrier.
What are L-carnitine’s main benefits?
L-Carnitine primarily benefits people with peripheral artery disease by reducing leg pain during exercise and improving exercise capacity, and it also potentially aids in muscle recovery and fertility in both men and women. Additionally, it may lower liver enzymes in people with nonalcoholic fatty liver disease and has minor positive effects on metabolic syndrome, including improvements in blood pressure, glucose, and lipids.
What are L-carnitine’s main drawbacks?
Supplementing with L-carnitine may cause a "fishy" odor in the breath and sweat, dry mouth, and gastrointestinal discomfort; nausea and gastric distress are the common adverse effects of propionyl-L-carnitine. Despite these drawbacks, meta-analyses suggest that L-carnitine and its derivatives are generally safe and well-tolerated, and daily doses up to 2,000 mg are considered safe.
How does L-carnitine work?
L-Carnitine helps transport long-chain fatty acids into the mitochondria for energy production and may also enhance antioxidant capacity, protect cellular membranes from oxidative stress, reduce inflammation, and increase nitric oxide levels. However, the exact mechanisms by which L-carnitine works are not fully understood and require further research.
What are other names for L-Carnitine?
Note that L-Carnitine is also known as:
- Acetyl-L-Carnitine
- ALCAR
- Acetylcarnitine
- L-Carnitine-L-Tartrate
- LCLT
- Glycine Propionyl-L-Carnitine
- GPLC
- Levocarnitine
- Levacecarnine
- L-3-hydroxytrimethylamminobutanoate
- carnitine
L-Carnitine should not be confused with:
- Carnosine (the product of beta-alanine)
Dosage information
The standard dose for L-carnitine is between 500–2000 milligrams per day (mg/day).
Supplementation with up to 2000 mg/day of L-carnitine is considered safe for humans.[1] There are various other forms of carnitine supplementation available: The equivalent dosage is up to about 2700 mg/day for acetyl-L-carnitine and up to about 2900 mg/day for propionyl L-carnitine.[1]
Frequently asked questions
L-carnitine is a compound produced in the body from lysine and methionine.[2][3] It is also found in food, primarily in meat products,[4][5] and can be taken as a supplement. L-carnitine can be acetylated to produce acetyl-L-carnitine (ALCAR), which is similar to L-carnitine but crosses the blood-brain barrier more efficiently.[6] L-carnitine is best known for its role in helping to ”shuttle” long-chain fatty acids into mitochondria to produce energy.[7][2]
Acetyl-L-carnitine is an acetylated form of L-carnitine that can cross the blood-brain barrier and is believed to have neurophysiological effects. It may help improve symptoms of depression and provide minor cognitive benefits, although more rigorous randomized controlled trials are needed to support these claims.
Acetyl-L-carnitine is an acetylated form of L-carnitine (i.e., it has an acetyl functional group attached to it) that can cross the blood-brain barrier, and is claimed to have neurophysiological effects.[6] Supplementation with acetyl-L-carnitine shows some efficacy in improving the symptoms of depression[35] as well as minor benefits to some aspects of cognitive function.[36][37][38] However, higher-quality randomized controlled trials are needed to bolster the current evidence in these areas.
Carnitine deficiency is rare and can occur in children with genetic metabolic disorders, with use of certain medications, or in people who are undergoing dialysis for chronic kidney disease. Although people who are on strict plant-based diets typically synthesize enough carnitine from other amino acids, supplementation may be used to treat symptoms in the case of deficiency, though more research is needed to confirm its effectiveness.
Although the main dietary source of carnitine is meat,[4][5] people who follow a strict plant-based diet typically do not have a higher risk of carnitine deficiency because sufficient amounts of carnitine can be synthesized in the body from other amino acids (e.g., lysine and methionine).[2][3]
In rare cases, carnitine deficiency can occur in children with inborn errors of metabolism (i.e., genetic defects affecting metabolic function) in carnitine biosynthetic or carnitine transport pathways.[39][40] Carnitine deficiency can also be caused by some drugs, including pivalic-acid-containing antibiotics and valproic acid, and it can occur in response to dialysis in people with chronic kidney disease.[39][40] In such cases, supplementation with carnitine is sometimes used to help treat the symptoms, but high-quality randomized controlled trials are needed to confirm its efficacy.[41][39][40]
L-Carnitine primarily benefits people with peripheral artery disease by reducing leg pain during exercise and improving exercise capacity, and it also potentially aids in muscle recovery and fertility in both men and women. Additionally, it may lower liver enzymes in people with nonalcoholic fatty liver disease and has minor positive effects on metabolic syndrome, including improvements in blood pressure, glucose, and lipids.
In people with peripheral artery disease (PAD), L-carnitine and propionyl-L-carnitine can help reduce a symptom called intermittent claudication (leg pain during exercise) and improve exercise capacity.[8][9][10] However, in healthy people, supplementation with L-carnitine does not appear to improve exercise capacity or performance.[11][12] That said, L-carnitine may help reduce exercise-induced muscle soreness and muscle damage, particularly following resistance exercise.[13]
Supplementation with L-carnitine or acetyl-L-carnitine may improve sperm quality in males with infertility.[14][15] Similarly, L-carnitine may improve ovulation and rate of pregnancy in women with polycystic ovary syndrome.[16][17] However, there are very few studies examining the effect of carnitine on fertility; further high-quality randomized controlled trials are needed.
Supplementation with L-carnitine and acetyl-L-carnitine can lower liver enzymes[18][19][20] in people with nonalcoholic fatty liver disease (NAFLD). Furthermore, L-carnitine may also have minor beneficial effects on metabolic syndrome. For example, supplementation with L-carnitine can improve blood pressure,[21][22] blood glucose,[23] blood lipids (including triglycerides,[18][21][24][25] total cholesterol,[24][25][26] LDL-c,[25][26] and HDL[25]), and markers of oxidative stress and chronic inflammation.[27] Some meta-analyses have also found a small (on the order of 1 kg) beneficial effect of supplementation with L-carnitine, acetyl-L-carnitine, or propionyl-L-carnitine on weight loss.[28][29][30] However, because studies often also include weight loss drugs or lifestyle interventions (exercise and/or diet-induced weight loss),[31][28][29][30] further high-quality studies are needed to isolate the effect of carnitine supplements on weight loss and other aspects of metabolic syndrome.
Supplementing with L-carnitine may cause a "fishy" odor in the breath and sweat, dry mouth, and gastrointestinal discomfort; nausea and gastric distress are the common adverse effects of propionyl-L-carnitine. Despite these drawbacks, meta-analyses suggest that L-carnitine and its derivatives are generally safe and well-tolerated, and daily doses up to 2,000 mg are considered safe.
Some studies report a “fishy” odor emanating from breath and sweat following supplementation with L-carnitine, which is likely due to the formation of trimethylamine.[32] Dry mouth and gastrointestinal discomfort have also been reported in some studies using L-carnitine,[33] while gastrointestinal problems (including nausea and gastric pain) are a common adverse effect of propionyl-L-carnitine.[9][10] However, several meta-analyses conclude that L-carnitine and its derivatives are generally safe and well‐tolerated.[18][9][10] Furthermore, supplementation of up to 2000 milligrams (mg) per day is considered safe for human consumption.[1] Some human studies have even used doses of L-carnitine as high as 6000 mg/day without serious side effects,[34] but a thorough safety evaluation of such high doses is lacking.[1]
L-Carnitine helps transport long-chain fatty acids into the mitochondria for energy production and may also enhance antioxidant capacity, protect cellular membranes from oxidative stress, reduce inflammation, and increase nitric oxide levels. However, the exact mechanisms by which L-carnitine works are not fully understood and require further research.
It’s not entirely clear how L-carnitine works. In tissues like muscle, L-carnitine is known to help “shuttle” long-chain fatty acids into mitochondria to produce energy.[7][2] Further evidence suggests that it may exert some of its potential beneficial effects by boosting antioxidant capacity, protecting cellular membranes from oxidative stress, reducing inflammation, and increasing nitric oxide levels.[3][6][2][7] Therefore, L-carnitine may work via several mechanisms, and further research is needed for a full understanding.
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