Carnitine and Thyroid DiseaseDecember 2007
By Julius G. Goepp, MD
Carnitine—The Latest Findings
As noted, virtually all of the modern work on carnitine in hyperthyroidism has come from the Italian research group led by Dr. Benvenga. Though their work is dramatic and compelling, scientists often have legitimate concerns about findings that haven’t been replicated or supported by additional researchers. In just the past two years, several new studies have come from completely different laboratories, each examining separate issues that together provide strong assurance of carnitine’s value for individuals who suffer from thyroid disease.
Specifically interested in the muscle weakness that accompanies both hyper- and hypothyroid conditions, Dr. Christopher Sinclair and colleagues at Brown Medical School in Rhode Island performed their own set of studies, which were published in 2005.6 The researchers obtained skeletal muscle samples from both hyper- and hypothyroid patients, as well as from a group of normal controls. Samples from patients with thyroid disease were also repeated after a course of appropriate traditional treatment. When they measured muscle carnitine content in the samples, the researchers found a significant reduction in hyperthyroid patients, with a return to normal levels as the condition improved under treatment. They found smaller, less significant decreases in muscle carnitine content in the hypothyroid group as well, which also improved with treatment. Dr. Sinclair and his colleagues, like their Italian counterparts, recognized that the decreased availability of carnitine in muscles means that “there will be less energy (in the form of long-chain fatty acids) transported into the mitochondria” and further point out that “this might lead to diminished fatty acid oxidation in skeletal muscle and, consequently, lead to weakness.”
A completely separate line of evidence about the importance of carnitine in protecting muscle integrity comes from the world of cancer treatment. In a 2005 study of a new chemotherapy drug called aplidine, French scientists included carnitine supplements to assure the safety of the new drug.29 Aplidine is a chemical derived from marine creatures called tunicates, or sea-squirts. It has potent anticancer effects but its dose is limited by myotoxicity, or muscle damage and weakness. When 3 of their 14 patients experienced toxicity from aplidine that limited their ability to increase the dose, the researchers simply provided oral carnitine. Carnitine was able to reverse the muscle toxicity, and patients who continued on the supplement were able to increase their chemotherapy doses by 40%. The researchers intend to conduct further studies of carnitine as a muscle protectant in future research.
There is no doubt that carnitine, a humble molecule used in the basic economics of cellular energy, holds the key to preventing and even reversing muscle damage and weakness from a variety of causes, including hyperthyroidism. Clinical trials investigating L-carnitine in thyroid conditions have utilized doses ranging from 2,000 to 4,000 mg daily. While these studies have focused on L-carnitine, advanced carnitine formulations such as acetyl-L-carnitine, acetyl-L-carnitine arginate, and propionyl-L-carnitine may also offer promise for individuals who suffer from thyroid conditions. More research is needed to determine which carnitine formulations are most beneficial for modulating the adverse effects of hyperthyroidism.
Carnitine is safe and has no known side effects, and is in widespread use for a number of indications, including the muscle fatigue that can result from strenuous exercise. The story of carnitine’s rise from obscurity is truly one of modern medical science’s most dramatic and compelling tales of success.
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