Thursday Oct 3, 2013 (foodconsumer.org) -- This is an overvirew of L-carnitine as a dietary supplement.  L-carnitine has been tested and may help to treat cardiovascular disease, myocardial infarction or heart disease, heart failure, angina pectoris, intermittent claudication in peripheral arterial disease, end-stage renal disease or hemodialysis, Alzheimer's disease, HIV/AIDS and decreased sperm motility among other things.

What is L-Carnitine?

L-carnitine is naturally biosynthesized in the liver and kidneys from amino acids lysin and methionine. There are a few different forms of carnitine including L-Carnitine, acetyl-L-carnitine, and propionyl-L-carnitine.  L-carnitine is found largely in meat and another animal-based foods like milk and cheese.  Humans can produce this compound, but some people like infants and people with certain conditions may have carnitine deficiency and high doses of carnitine supplements may also be used to prevent or treat certain diseases or health conditions.

Carnitine plays an important role in energy production by transporting long chain fatty acids into the mitochondira to "burn chem" and transporting toxic by-products out of this cellular organelle to prevent their accumulation.  Because of its role in energy production, sportsmen use this compound to boost their performance.  Skeletal and muscle tissues contain high levels of L-carnitine because these issues need high levels of energy.

Foods high in L-carnitine

Foods high in L-carnitine include meat, fish, poultry, and milk.  Interestingly, red meat, whose consumption is associated with high risk of heart disease, contains higher levels of L-carnitine, which benefits the heart.  Please note that the natural form of carnitine is L-carnitine.  D-carnitine results from a chemical synthesis and is not active in the body or useless and may potentially cause health problems.  In foods, only L-carnitine can be found. 

Carnitine deficiency

There are two types of carnitine deficiency, one caused by a genetic disorder or the cellular carnitine transporter system that manifests itself often by the age of five years and its symptoms include cardiomyopathy, skeletal muscle weakness and hypoglycemia.  Another type of carnitine dieficency can be caused by some disorders such as chronic renal failure or some medical conditions such as taking antibiotics that either prevent the absorption of this nutrient or increase the excretion of this compound.

If the deficiency is caused by a non-genetic factor, L-carnitine can be used as a dietary supplement to help increase the level of L-carnitine in the system.

Athletic performance

Because L-carnitine promotes energy production, people who need high energy output may benefit from taking this dietary supplement.  That is why some athletes take L-carnitine to improve performance.   Those who need extra energy such as those who experience fatigue or depression, may also benefit from taking this nutritional supplement.  Most people can take 2 to 6 grams of L-carnitine per day without any issue.

Anti-Aging

Calorie-restriction is not the only thing people can do to slow the aging process and extend their lifespan.    Studies suggest that L-carnitine can also have anti-aging properties.  (Any antioxidant can have some anti-aging properties)

A reduced mitochondrial function or production of energy is a sign of the normal or abnormal aging process.   L-carnitine is found at lower levels in the tissues of older people.  Animal studies have already found that supplementation of Acetyl-L-carnitine and alpha-lipoic acid (an antioxidant, which can dissolve in both water like vitamin C and lipids like vitamin E) can retard the mitochondrial decay or aging.  Animals fed a L-carnitine supplement were more energetic and moved more than control animals without exposure to this supplement. In addition, the study animals also improved their performance on memory-requiring tasks.

Human clinical trials have shown that supplementation of acetyl-L-carnitine may improve mental function and slow or prevent cognitive impairment or even dementia like Alzheimer's disease.  These trials used a dose of 1.5 to 3.0 grams per day of acetyl-L-carnitine for 3 to 12 months.

Cardiovascular disease, peripheral arterial disease

Studies have examined the effectiveness of supplemental l-carnitine in treating cardiac ischemia (restricted blood flow to the heart) and peripheral arterial disease (poor circulation in the legs or otherwise known as intermittent claudication) and found this supplement may counteract the toxic effect of free fatty acids and boost carbohydrate metabolism.

Short term studies have demonstrated anti-ischemic properties in patients with an acute anterior myocardial infarction or heart attack given orally or by injection of L-carnitine in a dose of 9 grams per day intravenously for the first five days and then 4 grams per day orally for six months.

A 2013 review of 12 small clinical trials combined with this Italian study led the researchers to conclude that L-carnitine supplementation reduced all-cause mortality, ventricular arrhythmias, and angina in people with an acute heart attack or myocardial infarction by 27, 65 and 40 percent respectively during a median 2-month follow-up.  But it did not reduce the risk of heart failure or recurrence of heart attack or myocardial infarction.

Research also indicates l-carnitine may improve the performance of skeletal muscles in the leg.  An European multicenter clinical trial tested 2 grams of propionyl-l-carnitine per day for 12 months in patients with moderate to severe claudication and found this supplementation significantly improved maximal walking distance and their quality of life, compared with controls.   A study conducted in the U.S. and Russia came to a similar conclusion that a 6-month L-carnitine supplementation can improve walking distance and speed, reduce bodily pain, enhance physical function and better quality of life.

Cancer patients

There are many things people can do to reduce their risk of cancer such as taking vitamin D, vitamin C, eating green leafy vegetables, garlic and avoiding red meat consumption and high intake of sugar and a high protein high fat diet all can prevent the development of cancer or fight cancer.  But L-carnitine may also help cancer patients.

L-carnitine helps cancer patients because these patients suffer fatigue resulting from chemotherapy, radiotherapy, poor intake and use of nutrients, and the disease itself.  These patients may experience L-carnitine deficiency.   At least one study shows that supplementation with L-carnitine in a dose of 4 grams per day for one week reduced fatigue in chemotherapy treated cancer patients and also normalized the serum level of L-carnitine.  Patients with terminal cancers who took L-carnitine supplements in a dose of 250 mg to 3000 mg per day also experienced an improvement in fatigue, mood and quality of life, according to another study.

Type 2 diabetes mellitus

Many people may have already known that curcumin and cinnomon can help prevent type 2 diabetes mellitus. Now research also suggests that taking L-carnitine can also benefit diabetics.

Insulin resistance, a symptom of type 2 diabetes mellitus, can not only affect glucose metabolism, but also be associated with defective fatty acid oxidation in muscle.  Because L-carnitine is involved in the normal fatty acid oxidation to produce energy, there may be a connection between insulin resistance/type 2 diabetes mellitus and L-carnitine levels.

Early studies have shown L-carnitine supplementation by injection may improve insulin sensitivity in type 2 diabetics and lower glucose levels in the blood.  One study shows that patients with either type 2 or type 2 diabetes mellitus supplemented with 3 grams of acetyl-L-carnitine per day orally for one year significantly relieved their nerve pain and improved vibration perception in patients with diabetic neuropathy.  The supplement worked particularly effectively in patients with type 2 diabetes of short duration.

HIV and AIDS

HIV carriers may suffer L-carnitine deficiency.  This is because HIV or other retroviruses or the drugs used to treat HIV or AIDS may cause mitochondrial toxicity and negatively affect mitochondrial fat metabolism.  That is also why HIV carriers often accumulate fat in some parts of the body and lose fat in others and develop hyperlipidemia and insulin resistance.

Research has shown that HIV infected individuals taking 2 to 6 grams of L-carnitine per day for weeks or months may slow the death of lymphocytes or slow the HIV progression and reduce risk of neuropathy and also favorably affect blood lipid concentrations.

End-stage renal disease, hemodialysis

Patients with kidney disease have their carnitine homeostasis impaired due to a few factors including reduced synthesis, increased elimination, and reduced intake due to poor appetite and low meat diet.  L-Carnitine deficiency is particularly troublesome in patients with end-stage renal disease or those on hemodialysis.  Because of carnitine deficiency in the blood and muscle, patients can experience anemia, muscle weakness, fatigue, altered concentrations of blood fat and even heart disorders.  Trials have already demonstrated that high doses of carnitine supplements orally or by injection can help eliminate at least some symptoms including anemia induced by carnitine deficiency.

Male infertility

Prior studies have shown that the carnitine content in seminal fluid is associated with sperm count and motility both of which are important for male fertility.  The findings suggest the natural compound may help treat male infertility.  The doses used in such studies are 2 to 3 grams of carnitine per day for 3 to 4 months.  Supplementation of L-carnitine can help both sperm quality and mobility.  These therapeutic benefits may be due to the fact that carnitine boosts mitochondrial fatty acid oxidation and provides more energy for sperm and also reduces cell death in the testes.

Weight Loss

Some people use L-carnitine as a weight loss supplement because some studies show that oral supplemental carnitine reduces fat mass, increases muscle mass, and fatigue.

Alzheimer's disease, Cognitive Impairment

Some studies show that carnitine supplements may help slow down the progression of dementia like Alzheimer's disease, help depression and improve cognitive performance in the elderly.

Carnitine dosages

Generally 1 to 3 grams of carnitine per day can be used.

Side effects of L-carnitine

L-carnitine is generally safe to use.  Some people may experience some side effects of L-carnitine at high doses such as nausea, vomiting, abdominal cramps, and diarrhea. 

Some reports suggest that intestinal bacterial may turn L-carnitine into a chemical called TMAO which may increase risk of cardiovascular disease.  However, consumers should know that this is a speculation.  Consumption of freshly cooked meat with high carnitine has rarely been linked to high risk of cardiovascular disease while processed meat which contains almost zero L-carnitine has been associated with cardiovascular disease.  This observation suggests that L-carnitine is actually not responsible for the risk of cardiovascular disease.

L-carnitine is generally well tolerated and considered a safe therapeutic agent.  However, it seems that researchers prefer using acetyl-L-carnitine in their studies because it can be absorbed better from the small intestine than L-carnitine and it can be easier for this compound to get into certain tissue such as brain tissue from the blood stream.