Carnitine helps your body release energy from fat. It is a compound most concentrated in tissues that rely on fats for energy: the skeletal muscles and the heart. Carnitine can come from production in the body, food or supplement. Supplemental carnitine come in three forms: L-carnitine, acetyl-L-carnitine, and L-propionyl carnitine. In the United States, only L-carnitine and acetyl-L-carnitine are available. Europe also gives the seal of approval to the use of L-propionyl carnitine.
Chemical Difference between L-carnitine and Acetyl-L-carnitine
Carnitine has two forms: L-carnitine and D-carnitine. They are mirror images of each other. Your body can only use L-carnitine. Taking D-carnitine can reduce the effectiveness of L-carnitine and is not recommended, according to the Office of Dietary Supplements. L-carnitine, acetyl-L-carnitine and L-propionyl carnitine all belong to the L-forms of carnitine, but with different attached groups. In addition to carnitine, acetyl-L-carnitine contains the attached acetyl group, which can be used to make an important nerve chemical acetylcholine.
Absorption of L-carnitine versus Acetyl-L-carnitine
The absorption of L-carnitine in the intestine is relatively low at 14 to 18 percent. Acetyl-L-carnitine has a better absorption rate. The Linus Pauling Institute states that acetyl-L-carnitine can be absorbed intact and that taking 2 g of acetyl-L-carnitine for 50 days raises the blood level of this compound by 43 percent. The absorption of both carnitine forms varies with diet, with meat eaters having a lower absorption rate than the vegetarians.
Functional Difference between L-carnitine and Acetyl-L-carnitine
Once absorbed, L-carnitine and acetyl-L-carnitine work in the same way to transport fats to mitochondria, the site in which fats are turned into energy. They also transport toxins built up from normal metabolism out of the mitochondria. In this way, they help to maintain the health of mitochondria and slow down aging. Acetyl-L-carnitine may have added benefits to the nerve tissues as it crosses the blood-brain-barrier and gets into the brain more readily. Hence, studies that evaluate the effectiveness of carnitine in Alzheimer's disease, memory decline and other brain diseases like to use acetyl-L-carnitine, notes by the University of Maryland Medical Center.
Availability and Dosage
L-carnitine is cheaper and available both as a prescription drug and as a dietary supplement. Acetyl-L-carnitine, on the other hand, is only used as a supplement. The usual doses for either L-carnitine or acetyl-L-carnitine are 1 to 3 g a day, according to the University of Maryland Medical Center. Although carnitine supplements are generally safe, you should consult with your physicians for the appropriate doses. Taking doses higher than 5 g a day may cause diarrhea, rash, abnormal appetite and body odor.
References
- The Office of Dietary Supplements; Carnitine: The Science behind a Conditionally Essential Nutrient; March 2004
- Linus Pauling Institute; L-Carnitine; April 2007
- The Office of Dietary Supplements; Carnitine
- The University of Maryland Medical Center; Carnitine (L-Carnitine); Steven D. Ehrlich, NMD; March 20, 2009
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