Carnitine deficiency is a metabolic disorder in which body levels of carnitine, an amino acid, is less than what is needed for the normal function of the body. Most people are able to consume enough carnitine in the normal diet to prevent a deficiency.
True carnitine deficiency is not known to occur in healthy people, and no studies have estimated the incidence of primary carnitine deficiency in the United States. International studies have found that it is rare, occurring 1 in 40,000 births in Japan and 1 in 15,500 births in the United Kingdom.
Primary and Secondary Deficiencies
A primary carnitine deficiency is a rare genetic disorder caused by a mutation in the protein that transports carnitine. The disorder presents in childhood and can be fatal without treatment. Other names for these conditions include carnitine palmitoyltranserase I or II deficiency and carnitine-acylcarnitine translocase deficiency.
Secondary carnitine deficiency, more common than primary deficiency, can result either from a genetic or an acquired condition that leads to depletion of carnitine. Hereditary causes include genetic defects in amino acid degradation or certain lipid disorders. Kidney disease can lead to an increased loss of carnitine in the urine. Other people at risk for developing carnitine deficiency include strict vegetarians, premature infants, and those in a rapid growth state, such as during pregnancy.
Because the most abundant source of carnitine in the American diet is animal foods, such as red meat and dairy products, those who follow a vegetarian or vegan diet may consume less. Some observational studies have found that those who eat an omnivorous diet (consuming meat) consume about 20 to 200 milligrams of carnitine a day, while those following a vegan diet may consume as little as 1 milligram a day. However, those who do not consume meat appear to synthesize enough carnitine from foods that contain the amino acids lysine or methionine, which the liver can convert into carnitine.
Vegetarian food sources of carnitine include tempeh, wheat, nuts and seeds, legumes, certain fruits and vegetables such as asparagus and avocado, and peanut butter. Many whole grains contain carnitine, such as buckwheat, corn, millet, oatmeal, rice bran, and wheat germ.
Vitamin C is essential for carnitine synthesis, so those with low dietary intakes of carnitine food sources should ensure they consume at least the daily recommended allowance of vitamin C from foods.
Premature infants are born with low stores of carnitine, which could put them at risk for a deficiency during rapid growth. Breastfed babies receive adequate carnitine from mothers' milk, as long as she is not deficient in the nutrient. Standard infant formulas, including soy formulas which are fortified with L-carnitine, contain adequate carnitine to support rapid infant growth.
Signs and Symptoms of Deficiency
In children, cardiomyopathy (an enlarged heart) is one sign of carnitine deficiency. Other signs of carnitine deficiency include muscle fatigue and weakness, abdominal cramps from decreased gastrointestinal motility, diarrhea, anemia and pre-mature aging.
Treatment of Deficiency
L-carnitine supplements are provided for those with both primary and secondary carnitine deficiencies. Oral carnitine is usually the first form of treatment, but if the individual does not respond, IV carnitine is available. Other nutritional counseling and supplementation is also considered, depending upon the cause of the deficiency. For example, for those with a fatty acid oxidation disorder, a fat-restricted diet is encouraged. Vitamins and minerals involved in the synthesis of carnitine may be needed, such as vitamin C, biotin or riboflavin.