Drug Database - Carnitine
L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine
Carnitine, derived from an amino acid, is found in nearly all cells of the body. Its name
is derived from the Latin carnus or flesh, as the compound was isolated from meat.
Carnitine is the generic term for a number of compounds that include L-carnitine,
acetyl-L-carnitine, and propionyl-L-carnitine.
Carnitine plays a critical role in energy production. It transports long-chain fatty acids
into the mitochondria so they can be oxidized ("burned") to produce energy. It also
transports the toxic compounds generated out of this cellular organelle to prevent their
accumulation. Given these key functions, carnitine is concentrated in tissues like
skeletal and cardiac muscle that utilize fatty acids as a dietary fuel.
The body makes sufficient carnitine to meet the needs of most people. For genetic or
medical reasons, some individuals (such as preterm infants), cannot make enough, so for
them carnitine is a conditionally essential nutrient.
Healthy children and adults do not need to consume carnitine from food or supplements, as
the liver and kidneys produce sufficient amounts from the amino acids lysine and
methionine to meet daily needs. The Food and Nutrition Board (FNB) of the National Academy
of Sciences reviewed studies on the functions of carnitine in 1989 and concluded it was
not an essential nutrient. The FNB has not established Dietary Reference Intakes
(DRIs)—including a recommended dietary allowance (RDA)—for carnitine
Foods That Provide Carnitine
Animal products like meat, fish, poultry, and milk are the best sources. In general, the
redder the meat, the higher its carnitine content. Dairy products contain carnitine
primarily in the whey fraction. The carnitine content of several foods is listed below:
- Beef steak, cooked, 4 ounces - Provides: 56-162mgs
- Ground beef, cooked, 4 ounces - Provides: 87-99mgs
- Milk, whole, 1 cup - Provides: 8mgs
- Codfish, cooked, 4 ounces - Provides: 4-7mgs
- Chicken breast, cooked, 4 ounces - Provides: 3-5mgs
- Ice cream, ½ cup - Provides: 3mgs
- Cheese, cheddar, 2 ounces - Provides: 2mgs
- Whole-wheat bread, 2 slices - Provides: 0.2mgs
- Asparagus, cooked, ½ cup - Provides: 0.1mgs
Carnitine occurs in two forms, known as D and L, that are mirror images (isomers) of each
other. Only L-carnitine is active in the body and is the form found in food.
Current Issues & Controversies
Carnitine has been studied extensively because it is important to energy production and is
a well-tolerated and generally safe therapeutic agent. Researchers prefer to use
acetyl-L-carnitine in research studies because it is better absorbed from the small
intestine than L-carnitine and more efficiently crosses the blood-brain barrier (i.e.,
gets into brain tissue).
Some athletes take carnitine to improve performance. However, twenty years of research
finds no consistent evidence that carnitine supplements can improve exercise or physical
performance in healthy subjects—at doses ranging from 2-6 grams/day administered for 1 to
28 days. (The total body content of carnitine is about 20 grams in a man weighing 155
pounds, almost all of it in the skeletal muscle.) For example, carnitine supplements do
not appear to increase the body's use of oxygen or improve metabolic status when
exercising, nor do they necessarily increase the amount of carnitine in muscle.
A decline in mitochondrial function is thought to contribute to the aging process.
Carnitine may be involved because its concentration in tissues declines with age and
thereby reduces the integrity of the mitochondrial membrane. Research in aged rats found
supplementation with high doses of acetyl-L-carnitine and alpha-lipoic acid (an
antioxidant) to reduce mitochondrial decay. The animals also moved about more and improved
their performance on memory-requiring tasks. At present there are no equivalent studies of
this kind in humans. However, a meta-analysis of double-blind, placebo-controlled studies
suggests that supplements of acetyl-L-carnitine may improve mental function and reduce
deterioration in older adults with mild cognitive impairment and Alzheimer's disease. In
these studies, subjects took 1.5-3.0 grams/day of acetyl-L-carnitine for 3-12 months.
Cardiovascular and Peripheral-Arterial Disease
Several studies have examined supplemental carnitine in the management of cardiac ischemia
(restriction of blood flow to the heart) and peripheral arterial disease (of which the
most important symptom is poor circulation in the legs, known as intermittent
claudication). Because levels of carnitine are low in the failing heart muscle,
supplemental amounts might be beneficial to the organ by counteracting the toxic effects
of free fatty acids and improving carbohydrate metabolism. In short-term studies,
carnitine has demonstrated anti-ischemic properties when given orally and by injection. A
double-blind, placebo-controlled, multicenter clinical trial in Italy with patients who
had suffered a first heart attack found that supplemental carnitine (given intravenously
for five days, then 6 grams/day orally for one year) reduced heart failure and overall
mortality. The results were not conclusive but promising enough to justify a larger study
whose results have not yet been reported.
Claudication results from an inadequate supply of oxygen-rich blood to the legs and leads
to an accumulation of acetylcarnitine in muscle due to its incomplete utilization.
Patients with peripheral arterial disease who develop claudication have significant
impairments in exercise performance and find it difficult to walk even short distances at
a slow speed. Two published randomized, controlled trials raise the possibility that
carnitine may improve the performance of skeletal muscles in the leg. In one European
multicenter clinical trial, subjects with moderate to severe claudication who were
supplemented with L-carnitine (in the form of propionyl-L-carnitine at 2 grams/day for 12
months) significantly improved their maximal walking distance and perceived quality of
life as compared to subjects receiving the placebo. A similar multicenter trial in the
United States and Russia found the same daily dose and form of carnitine administered for
6 months in patients with disabling claudication to significantly improve walking distance
and speed, reduce bodily pain, enhance physical function, and improve perceived health
state as compared to controls.
Fatigue resulting from chemotherapy, radiation treatment, and poor nutritional status is
common in cancer patients. They may also be deficient in carnitine. In one study,
treatment with carnitine supplements (4 grams/day for one week) ameliorated fatigue in
most chemotherapy-treated subjects and restored normal blood levels of carnitine. In
another trial, terminal cancer patients supplemented with carnitine (doses ranged from 250
milligrams to 3 grams/day) experienced less fatigue and improved mood and quality of
sleep. In both studies, most subjects were carnitine deficient before taking the
Type 2 diabetes
Insulin resistance, which plays an important role in the development of type 2 diabetes,
may be associated with a defect in fatty-acid oxidation in muscle. This raises the
question as to whether mitochondrial dysfunction might be a factor in the development of
the disease. Increased storage of fat in lean tissues has become a marker for insulin
resistance. Early research suggests that supplementation with L-carnitine intravenously
may improve insulin sensitivity in diabetics by decreasing fat levels in muscle and may
lower glucose levels in the blood by more promptly increasing its oxidation in cells. A
recent analysis of two multicenter clinical trials of subjects with either type 1 or type
2 diabetes found that treatment with acetyl-L-carnitine (3 grams/day orally) for one year
provided significant relief of nerve pain and improved vibration perception in those with
diabetic neuropathy. The treatment was most effective in subjects with type 2 diabetes of
HIV and AIDS
The human immunodeficiency virus (HIV) causes a decline in the number of lymphocytes (one
type of white blood cell), resulting in acquired immunodeficiency syndrome (AIDS).
HIV-infected individuals often accumulate fat in some areas of the body and lose fat in
others and develop high levels of blood fats (hyperlipidemia) and insulin resistance,
which together constitute the lipodystrophy syndrome. This syndrome may represent
mitochondrial toxicity brought about by the HIV infection and the antiretroviral drugs
used to treat it, and can induce a carnitine deficiency that limits mitochondrial fat
metabolism. The molecular mechanisms by which this occurs are poorly understood.
Preliminary research provides conflicting findings but suggests that supplementation with
carnitine both intravenously and orally (at doses of 2-6 grams/day for weeks or months) in
HIV-infected individuals may slow the death of lymphocytes (which in turn may slow HIV
progression), reduce neuropathy, and favorably affect blood lipid levels.
At doses of approximately 3 grams/day, carnitine supplements may cause:
- abdominal cramps
- "fishy" body odor
More rare side effects include:
- muscle weakness in uremic patients
- seizures in those with seizure disorders
Carnitine interacts with pivalate-conjugated antibiotics such as pivampicillin that are
used in the long-term prevention of urinary-tract infections. Chronic administration of
these antibiotics increases the excretion of pivaloyl-carnitine, which can lead to
carnitine depletion. However, while tissue carnitine levels may become low enough to limit
fatty acid oxidation, no cases of illness due to deficiency have been described. Blood
concentrations of carnitine may be reduced in children treated for convulsions with
phenobarbital, valproic acid, phenytoin, or carbamazepine, but no clinical consequences
have been shown.
Carnitine can impair thyroid hormone action, so you shouldn't take it if your thyroid
hormone levels are low or borderline low. It's also not recommended for anyone on
dialysis. Carnitine has a higher risk of negative interactions with other supplements, so
be sure to talk to your doctor and/or pharmacist before taking it. It may be helpful to
have a list of all of the medications and supplements you are taking ready for that
SERIOUS SIDE EFFECTS:
- Rapid heart rate
- Increase in blood pressure
LESS SERIOUS Effects:
- Stuffy nose
- Difficulty sleeping
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