Everything about Carnitine totally explained
Carnitine is a
quaternary ammonium compound biosynthesized from the
amino acids lysine and
methionine. In living cells, it's required for the transport of
fatty acids from the
cytosol into the
mitochondria during the breakdown of
lipids (or fats) for the generation of metabolic energy. It is often sold as a
nutritional supplement. Carnitine was originally found as a
growth factor for
mealworms and labeled
vitamin Bt. Carnitine exists in two
stereoisomers: its biologically active form is
L-carnitine, while its
enantiomer,
D-carnitine, is biologically inactive.
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Production
In animals, carnitine is biosynthesized primarily in the
liver and
kidneys from the amino acids
lysine or
methionine .
Vitamin C (
ascorbic acid) is essential to the synthesis of carnitine. During
growth or
pregnancy the requirement of carnitine might exceed its natural production.
Role in fatty acid metabolism
Carnitine transports long-chain acyl groups from fatty acids into the
mitochondrial matrix, so that they can be broken down through
β-oxidation to
acetate to obtain usable energy via the
citric acid cycle. In some organisms such as fungi, the acetate is used in the
glyoxylate cycle for
gluconeogenesis and formation of
carbohydrates. Fatty acids must be activated before binding to the carnitine molecule to form
acyl-carnitine. The free fatty acid in the cytosol is attached with a
thioester bond to
coenzyme A (CoA). This reaction is catalyzed by the enzyme
fatty acyl-CoA synthetase and driven to completion by
inorganic pyrophosphatase.
The acyl group on CoA can now be transferred to carnitine and the resulting acyl-carnitine transported into the mitochondrial
matrix. This occurs via a series of similar steps:
- Acyl-CoA is conjugated to carnitine by carnitine acyltransferase I (palmitoyltransferase) located on the outer mitochondrial membrane
- Acyl-carnitine is shuttled inside by a carnitine-acylcarnitine translocase
- Acyl-carnitine is converted to acyl-CoA by carnitine acyltransferase II (palmitoyltransferase) located on the inner mitochondrial membrane. The liberated carnitine returns to the cytosol.
Human genetic disorders such as
primary carnitine deficiency,
carnitine palmitoyltransferase I deficiency,
carnitine palmitoyltransferase II deficiency and
carnitine-acylcarnitine translocase deficiency affect different steps of this process.
Carnitine acyltransferase I undergoes
allosteric inhibition as a result of
malonyl-CoA, an intermediate in fatty acid biosynthesis, in order to prevent futile cycling between β-oxidation and fatty acid synthesis.
Effects on bone mass
In the course of human aging, carnitine concentration in cells diminishes affecting fatty acid metabolism in various tissues. Particularly adversely affected are bones which require continuous reconstructive and metabolic functions of osteoblasts for maintenance of bone mass.
There is a close correlation between changes in plasma levels of
osteocalcin and
osteoblast activity and a reduction in osteocalcin plasma levels is an indicator of reduced osteoblast activity, which appears to underlie
osteoporosis in elderly subjects and in postmenopausal women. Administration of a carnitine mixture or propionyl-
L-carnitine is capable of increasing serum osteocalcin concentrations of animals thus treated, whereas serum osteocalcin levels tend to decrease with age in control animals.
Antioxidant effects
The carnitines exert a substantial
antioxidant action, thereby providing a protective effect against lipoperoxidation of phospholipid membranes and against oxidative stress induced at the myocardial and endothelial cell level.
Effects on diabetes
L-Carnitine improved glucose disposal among 15 patients with
type II diabetes and 20 healthy volunteers. Glucose storage increased between both groups, but glucose oxidation increased only in the diabetic group. Finally, glucose uptake increased about 8% for both.
Food sources
The highest concentrations of carnitine are found in
red meat and dairy products. Other natural sources of carnitine include
nuts and
seeds (for example
pumpkin,
sunflower,
sesame),
legumes or
pulses (
beans,
peas,
lentils,
peanuts),
vegetables (
artichokes,
asparagus,
beet greens,
broccoli,
brussels sprouts,
collard greens,
garlic,
mustard greens,
okra,
parsley),
fruits (
apricots,
bananas),
cereals (
buckwheat,
corn,
millet,
oatmeal, rice
bran,
rye,
whole wheat, wheat
bran,
wheat germ) and other 'health' foods (
bee pollen,
brewer's yeast,
carob, and
kale).
| Product |
Quantity |
Carnitine |
| Beef Steak |
3.5 oz |
95 mg |
| Ground Beef |
3.5 oz |
94 mg |
| Pork |
3.5 oz |
27.7 mg |
| Bacon |
3.5 oz |
23.3 mg |
| Tempeh |
half cup |
19.5 mg |
| Cod Fish |
3.5 oz |
5.6 mg |
| Chicken Breast |
3.5 oz |
3.9 mg |
| American Cheese |
3.5 oz |
3.7 mg |
| Ice Cream |
3.5 fl oz |
3.7 mg |
| Whole Milk |
3.5 fl oz |
3.3 mg |
| Avocado |
one medium |
2 mg |
| Cottage Cheese |
3.5 fl oz |
1.1 mg |
| Whole Wheat Bread |
3.5 oz |
0.36 mg |
| Asparagus |
3.5 oz |
0.195 mg |
| White Bread |
3.5 oz |
0.147 mg |
| Macaroni |
3.5 oz |
0.126 mg |
| Peanut Butter |
3.5 oz |
0.083 mg |
| Rice (cooked) |
3.5 oz |
0.0449 mg |
| Eggs |
3.5 oz |
0.0121 mg |
| Orange Juice |
3.5 fl oz |
0.0019 mg |
Generally, 20 to 200 mg/day are ingested per day by those on an
omnivorous diet, while those on a strict
vegetarian or
vegan diet may ingest as little as 1 mg/day.
Other sources
Other sources may be found in over-the-counter
vitamins,
energy drinks and various other products. Products containing
L-carnitine can't be marketed as "natural health products" in
Canada.
L-Carnitine products and supplements are not allowed to be imported into Canada (
Health Canada).
As a weight loss supplement
"Although
L-carnitine has been marketed as a weight-loss supplement, there's no scientific evidence to date to show that it improves weight loss. A recent study of moderately overweight women found that
L-carnitine didn't significantly alter body weight, body fat, or lean body mass. Based on the results of this one small study, claims that
L-carnitine helps reduce weight are not supported at this time."
Further Information
Get more info on 'Carnitine'.
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