Physiological effects of Carnitine

As an example of normal synthesis, a 70 kg (150 lb) person would produce 11-34 mg of carnitine per day. Adults eating a diet mixed with red meat and other animal products consume about 60-180 mg of carnitine per day, while vegans consume about 10-12 mg per day.The majority (54–86%) of carnitine obtained from the diet is absorbed in the small intestine before entering the bloodstream.The total amount of carnitine in a 70 kg (150 lb) human body is approximately 20 g (0.71 oz), almost all of which is contained in skeletal muscle cells.Carnitine is metabolized at a rate of approximately 400 μmol (65mg) per day, less than 1% of total body stores.

Deficiency 

Carnitine deficiency is rare in healthy people without metabolic disorders, suggesting that most people have normal, adequate levels of carnitine,which is normally produced through fatty acid metabolism.One study found no signs of carnitine deficiency in vegans.Infants, especially premature infants, are low in carnitine and require carnitine-fortified infant formula instead of breast milk when necessary.There are two types of carnitine deficiency states. Primary carnitine deficiency is an inherited disorder of the cellular carnitine transport system that usually presents by age five and is associated with cardiomyopathy, skeletal muscle weakness, and hypoglycemia.Secondary carnitine deficiency can be the result of certain conditions, such as chronic renal failure, or in conditions that reduce carnitine absorption or increase its excretion, such as antibiotic use, malnutrition, and postdigestive Malabsorption.

Supplementation

Although athletes are generally interested in using carnitine to improve athletic performance, inhibit muscle spasms, or enhance recovery from physical training, the quality of research on these possible benefits has been low and no effect conclusions can be drawn.With supplementation of 2-6 grams (0.071-0.212 oz) per day for one month, there is no consistent evidence that carnitine affects exercise or physical performance.Carnitine supplementation does not improve oxygen consumption or metabolic function during exercise, nor does it increase carnitine levels in muscle.There is no evidence that L-carnitine affects fat metabolism or aids in weight loss.

Male fertility

Carnitine levels in semen are directly related to sperm count and motility,suggesting the compound may have value in treating male infertility.

Diseases

Carnitine has been studied in a variety of cardiometabolic conditions, indicating that it is being pilot investigated for its potential as an adjunct to heart disease and diabetes, among many other conditions.Carnitine had no effect on the prevention of all-cause mortality associated with cardiovascular disease,and had no significant effect on blood lipids.Although there is some evidence from meta-analyses that L-carnitine supplementation improves cardiac function in people with heart failure, there has not been enough research to determine its overall efficacy in reducing risk or treating cardiovascular disease.Only preliminary clinical studies have shown that using L-carnitine supplements can improve symptoms of type 2 diabetes,such as improving glucose tolerance or reducing fasting blood sugar levels.The kidneys contribute to the body's overall homeostasis, including carnitine levels. In the setting of renal impairment, increased urinary excretion of carnitine, decreased endogenous synthesis, and malnutrition due to disease-induced anorexia can lead to carnitine deficiency.Carnitine had no effect on most parameters of end-stage renal disease, although it may reduce C-reactive protein, a biomarker of systemic inflammation.Carnitine blood levels and muscle stores may become low, which can lead to anemia, muscle weakness, fatigue, changes in blood lipid levels, and heart disease.Some research suggests that supplementation with high doses of L-carnitine (usually injected) may help manage anemia.