Carnitine

Carnitine is a compound that is naturally present in our body. It is the generic name for several compounds including L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine. Although, it is often classified as an amino acid, L-carnitine is a compound related to the B vitamins. In the 1950s, when it was first studied, L-carnitine was called vitamin BT. 

For the body to produce sufficient amounts of L-carnitine, the body also needs plenty of vitamin C. In addition to the L-carnitine naturally present in your body, you can also get small amounts of it from diet by consuming animal products like meat and fish.

L-carnitine is produced in the kidneys and liver from the amino acids lysine and methionine. However, it is stockpiled elsewhere in the body, mainly in muscle, the brain, and in sperm. In diet, it is primarily found in meat and other animal products. Although, L-carnitine can be found in some plant foods such as avocado and soybeans, meat (redder the better) is the best source for it.

L-carnitine is often taken as a weight loss supplement. Acetyl L-carnitine (ALCAR), is another favored supplemental form of L-carnitine. ALCAR is present throughout the central nervous system, where it plays an important part in producing energy. The acetyl batch connected to the carnitine molecule boosts its ability to cross the blood-brain barrier and gain access to the brain, where it functions as a potent antioxidant. Because of this mechanism, some scientists believe that acetyl-L-carnitine may protect against aging processes and neurodegeneration.

 

How does L-carnitine potentially promote muscle health?

Under normal physiologic conditions such as sitting, gentle walking, and lying; L-carnitine facilitates the transport of fatty acids into the mitochondria.

The mitochondria is the power generator of the cell and its favorite fuel is fat. The mitochondria turns fatty acids into packets of energy called ATP. The more ATP your mitochondria produces the more energy you have. The cell uses this energy to repair damaged internal machinery and support normal cellular function.

Theoretically, insufficient L-carnitine in muscle cells limits the amount of energy the mitochondria produces, and  insufficient energy places muscle at risk for injury and dysfunction.

Under intense conditions such as vigorous exercise, weight lifting, running, dancing, etc; L-carnitine sill helps maintain mitochondrial ATP production, but via a slightly different mechanism.

Optimal L-carnitine levels ensure sufficient availability of co-enzyme A. Co-enzyme A is a special enzyme that allows mitochondria to use fat as a fuel source for energy production. As long as the mitochondria continues to produce adequate amounts of energy than muscle cells do not need to expend their sugar stores as an energy source. When sugar stores are depleted than muscle fatigues and soreness sets in.

Potentially, L-carnitine may improve endurance allowing performance of  higher intensity activity for a prolonged period of time. This may generate a greater stimulatory signal leading to greater gains in strength and muscle mass.

Researchers from Queen’s Medical Center evaluated the effect of  2 g of L-carnitine-and 80 g of carbohydrate twice daily for 24 weeks  on energy metabolism and athletic performance. The authors concluded L-carnitine supplementation resulted in muscle glycogen sparing during low intensity exercise and reduced muscle anaerobic ATP production in high intensity exercise. These changes were associated with an improvement in exercise performance. (Wall et al. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. J Physiol 589.4 (2011) pp 963–973)

Italian investigators examined the influence of L-carnitine administration on maximal exercise. The authors concluded treatment with 2 grams of L-carnitine significantly increased both maximal oxygen uptake and power output in subjects compared to placebo. (Vecchiet et al. Influence of L-carnitine administration on maximal physical exercise. Eur J Appl Physiol Occup Physiol. 1990;61(5-6):486-90.)

Other potential health benefits of carnitine?

Carnitine and weight loss

Several studies have been conducted to investigate if carnitine is effective as a weight loss supplement. However, the conclusions of both human and animal studies produced mixed results.

In one study involving 38 women, participants were divided into 2 groups: one group received L-carnitine supplement, while the other didn’t. Both groups took part in 4 exercise sessions each week for 8 weeks. No difference in weight loss was found between the 2 groups, although five participants in the L-carnitine group experienced nausea or diarrhea.

In another study, researchers discovered that participants performing a 90-minute stationary bicycle exercise for four weeks didn’t burn more fat even after taking L-carnitine supplements during the entire study period.

However, in an analysis of 9 studies conducted on obese individuals or the elderly found that the participants taking L-carnitine supplements during exercise lost an average of 2.9 lbs more weight.

Researchers say that more studies are called for in order to confirm the advantages of L-carnitine in young people.

 

Aging and cognition

The aging process is thought to be caused by a decrease in mitochondrial function. Scientists believe carnitine may be a part of the process because its accumulation in tissues decreases with age and thereby diminishes the durability of the mitochondrial membrane. A study on aged rats showed that the rats fed high doses of acetyl-L-carnitine and an antioxidant called alpha-lipoic acid had reduction in the mitochondrial deterioration. The rodents also experienced improvement in their movements and memory-requiring tasks. In a human study, older adults were given 1.5-3.0 gm/day of ALCAR for 3–12 months. A meta-analysis conducted on double-blind, placebo-controlled studies on humans showed that older adults with mild cognitive impairment and Alzheimer’s disease, who received 1.5-3.0 gm/day of ALCAR for 3–12 months experienced enhanced mental function.

According to studies, L-carnitine supplements were beneficial in several other conditions such as:

  • Type 2 diabetes
  • Cardiovascular and peripheral arterial disease
  • End-stage renal disease and hemodialysis
  • HIV and AIDS
  • Male infertility

 

Are there any side-effects?

Carnitine supplements, when taken at doses of about 3 gm/day, can cause vomiting, nausea, diarrhea, abdominal cramps, and a fishy odor in the body. Other less common side effects may be muscle weakness (in people with uremia) and seizures in people with the disorder.

Some studies have indicated that carnitine forms a substance called TMAO when it is metabolized by the intestinal bacteria. TMAO levels predict cardiovascular disease (CVD) risk. This effect is stronger in meat eaters than in vegetarians. More studies are needed to understand the implications of these findings.

 

What are the best natural sources of carnitine?

The best sources of carnitine are meat (the redder the meat, the higher the carnitine), fish, poultry and milk. In, dairy products, carnitine is generally present in the whey part. These are some of the foods with considerable amounts of carnitine:

Table 1: Selected food sources of carnitine

Food

Carnitine content

Beef steak (4 ounces, cooked)

56–162 mg

Ground beef (4 ounces, cooked)

87–99 mg

Milk (1 cup, whole)

8

Codfish (4 ounces, cooked)

4–7

Chicken breast (4 ounces, cooked)

3–5

Ice cream, ½ cup

3

Cheese (cheddar, 2 ounces)

2

Whole-wheat bread (2 slices)

0.2

Asparagus (½ cup, cooked)

0.1

 

References

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