Carnitine:

September 2001

Carnitine: An Essential Nutrient? By Karen Plawecki, M.S., R.D.Contributing Editor

Carnitine is a critical substance needed for the maintenance of health, but is not a required nutrient in the diet. Classified as an amino acid, carnitine is used as a carrier to transport long-chain fatty acids into the mitochondria of a cell for beta-oxidation to produce energy. This reaction is carried out by the use of different enzymes.

Since fatty acids are the body’s predominant energy source, the carnitine shuttle is critical to producing an adequate amount of energy to operate the body. A deficiency in carnitine, or a defect in the enzymes or pathway, can lead to increased serum fatty-acid levels and reduced levels of blood glucose to compensate for the lack of energy from fatty acids.

High-risk groupsThe primary dietary sources of carnitine include meat, especially beef, and dairy products. While there is no set dietary requirement for carnitine, the body can adequately synthesize it from the amino acids lysine and methionine.

Vegans, infants and nursing mothers have been listed as at-risk for carnitine deficiency. However, for well-nourished individuals, regardless of diet, carnitine is not a dietary essential. For those with inborn defects, or if the pathway is interrupted (possibly from liver or kidney problems), carnitine becomes essential and a supplement is required. For these rare cases, carnitine actually is prescribed as medication.

Therapeutic dosage and safetySafe dosages of carnitine are 2.0 to 6.0 grams. Most studies have used 0.5 grams to 2.0 grams given three times a day. L-carnitine, L-acetyl-carnitine (LCA), propionyl L-carminative and acetyl-L-carnitine (ALC) are the forms that have proven safe. D-carnitine actually can interfere with carnitine function, leading to muscle weakness.

Common side effects of carnitine supplementation beyond safe doses include stomach cramps, diarrhea, headache, nausea or vomiting.

Carnitine claimsBeneficial for energy and endurance levels, carnitine also aids in heart, nerve and immune-system functions. These claims are based on therapeutic, supplemental doses of carnitine, and most of the studies are based on a small sample size.

Energy enhancement and sports performance. Theoretically, additional carnitine would promote greater lipid oxidation for energy resulting in a more efficient use of glucose, which delays fatigue. This theory, however, does not hold up under testing. Most studies showed no benefit in energy metabolism or muscle recovery. Also, no additional weight or fat loss occurred with supplementation.

Heart health. The heart relies heavily on fat as an energy source, so it is susceptible to a carnitine deficiency. Most of the studies have focused on treating specific forms of heart disease in conjunction with conventional treatment. Positive results have been shown in people with angina (chest pain), claudication (poor circulation), heart attack and congestive heart failure. The studies are small, but promising.

Memory. Some double-blind studies indicate that acetyl-L-carnitine helps to preserve some mental function or slow the effects of dementia, including Alzheimer’s disease. Some other studies showed no benefit.

Immune function/AIDS. AIDS patients show symptoms of carnitine deficiency, and supplementing carnitine has improved their immune system parameters. Whether or not this helps to slow the disease still needs to be investigated.

Chronic Fatigue Syndrome. Preliminary work has indicated that carnitine improves outcomes and functional ability.

Additional claims. Carnitine has been claimed to help male fertility, Down’s syndrome, and muscular dystrophy, but there is minimal, if any, work in this area.

Take-home messageThe claims for carnitine have two common points: carnitine is used as part of a therapeutic regimen, not a nutrient source; and additional work needs to be done to better determine carnitine’s role in disease prevention and treatment.

From a nutritional standpoint, the best way to ensure adequate carnitine levels is to consume either meat or dairy products, or consume an adequate amount of the essential amino acids for the body to produce carnitine.

Karen Plawecki, a registered dietitian, earned her master’s degree in nutrition with an emphasis in food science from Purdue University. Currently, she teaches a nutrition and food course at the University of Illinois, Urbana-Champaign.

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