Overview
Lipoic acid, also known as alpha-lipoic acid, is a sulfur-containing fatty acid. It is found inside every cell of the body, where it helps generate the energy that keeps humans alive and functioning. Lipoic acid is a key part of the metabolic machinery that turns glucose (blood sugar) into energy for the body’s needs.
Lipoic acid is an antioxidant, which means that it
neutralizes naturally occurring but harmful chemicals known as free
radicals. Unlike other antioxidants, which work only in water or
fatty tissues, lipoic acid is unusual in that it functions in both water and fat.
By comparison, vitamin E works only in fat, and vitamin C works only in water.
This gives lipoic acid an unusually broad spectrum of antioxidant action.
Lipoic acid also may help regenerate other antioxidants that have been used up. In addition, lipoic acid may be able to do the work of other antioxidants when the body is deficient in them.
It is thought that certain nerve diseases are at least partially caused by damaging free radicals. Because of its combined fat and water solubility, lipoic acid can get into all the parts of a nerve cell and potentially protect it against such damage. This is the rationale for studies on the potential benefits of lipoic acid for diabetic neuropathy.
Sources
A healthy body makes enough lipoic acid to supply its requirements; external
sources are not necessary. However, several medical conditions appear to be
accompanied by low levels of lipoic acid (specifically diabetes, liver
cirrhosis, and atherosclerosis), which suggests (but
does not prove) that supplementation would be helpful. Liver and yeast contain
some lipoic acid. Nonetheless, supplements are necessary to obtain therapeutic
dosages.
Therapeutic Dosages
The typical dosage of oral lipoic acid for treating complications of
diabetes is 100 to 200 milligrams (mg) three times daily. In
studies that found benefits, several weeks of treatment were often necessary for
full effects to develop.
For use as a general antioxidant, a lower dosage of 20 to 50 mg daily is commonly recommended, although there is no evidence that taking lipoic acid in this way offers any health benefit.
Therapeutic Uses
Lipoic acid has been widely used for decades in Germany to treat diabetic peripheral neuropathy. This is a condition caused by diabetes in which nerves leading to the arms and legs become damaged, resulting in numbness, pain, and other symptoms. Free radicals are hypothesized to play a role in neuropathy, and on this basis, lipoic acid has been tried as a treatment. However, the evidence for benefit is largely limited to studies that used the intravenous form of this supplement.
Another set of nerves also may become damaged in diabetes: the autonomic nerves that control internal organs. When this occurs in the heart (cardiac autonomic neuropathy), it leads to irregularities of heart rhythm. There is some evidence that lipoic acid supplements may be helpful for this condition.
Preliminary and sometimes contradictory evidence suggests that lipoic acid may improve other aspects of diabetes, including blood sugar control and the development of long-term complications, such as diseases of the heart, kidneys, and small blood vessels.
Mixed evidence exists for the benefits of lipoic acid in the treatment of burning mouth syndrome, a condition characterized by unexplained scalding sensations in the mouth. Weak evidence hints that use of lipoic acid might help prevent migraine headaches. A cream containing 5 percent lipoic acid has shown promise for the treatment of sun-damaged skin.
One animal study suggests that lipoic acid might help prevent age-related
hearing loss. Similarly weak evidence hints that lipoic acid might be helpful for
glaucoma and for reducing the side effects (specifically, cardiac toxicity) of the
cancer chemotherapy drug doxorubicin. Other uses for which
lipoic acid has been proposed include preventing cancer and heart disease and
treating or preventing cataracts.
Scientific Evidence
Diabetic peripheral neuropathy. There is some evidence that intravenous lipoic acid can reduce symptoms of diabetic peripheral neuropathy, at least in the short term. However, the evidence for oral lipoic acid remains weak and contradictory.
For example, a double-blind, placebo-controlled study of five hundred people with diabetic neuropathy found that intravenous lipoic acid helped reduce symptoms over a three-week period; however, long-term oral supplementation did not prove effective.
Benefits were seen with oral lipoic acid in a study published in 2006. In this double-blind, placebo-controlled trial, 181 people with diabetic peripheral neuropathy were given either placebo or one of three doses of lipoic acid: 600, 1,200, or 1,800 mg daily. Over the five-week study period, benefits were seen in all three lipoic acid groups compared with the placebo group.
While this outcome may sound promising, one feature of the results tends to
reduce the faith one can put in them: the absence of a dose-related effect.
Ordinarily, when a treatment is effective, higher doses produce relatively better
results. When such a spectrum of outcomes is not observed, the study becomes
questionable. Other than this one study, the positive evidence for oral lipoic
acid in diabetic peripheral neuropathy is limited to open studies of minimal to no
validity and double-blind trials too small to be relied upon. There is some
preliminary evidence that lipoic acid could be more effective if it were combined
with gamma-linolenic acid, another supplement used for diabetic
peripheral neuropathy.
Diabetic autonomic neuropathy. There is better evidence for oral lipoic acid in a form of diabetic neuropathy affecting the nerves that supply the heart: autonomic neuropathy. Not only does diabetes damage the nerves in the arms and legs; it can also affect deep nerves that control organs such as the heart and digestive tract.
The Deutsche Kardiale Autonome Neuropathie study followed seventy-three people with diabetes who had symptoms caused by nerve damage affecting the heart. Treatment with 800 mg daily of oral lipoic acid showed statistically significant improvement compared with placebo and caused no significant side effects.
Burning mouth syndrome. Persons with burning mouth syndrome (BMS) feel chronic scalding pain in the mouth, as if they had consumed an excessively hot drink. Although the cause of BMS is not known, the symptoms resemble those of neuropathy, and for that reason, researchers have investigated the potential benefits of lipoic acid.
In a two-month, double-blind trial involving sixty people with BMS, the use of lipoic acid significantly reduced symptoms, compared with placebo. However, three small double-blind trials failed to find any benefit for lipoic acid.
Safety Issues
Lipoic acid appears to have no significant side effects at dosages up to 1,800 mg daily. Safety for young children, women who are pregnant or nursing, and those with severe liver or kidney disease has not been established.
Bibliography
Carbone, M., et al. “Lack of Efficacy of Alpha-Lipoic Acid in Burning Mouth Syndrome.” European Journal of Pain 13, no. 5 (2009): 492-496.
Cavalcanti, D. R., and F. R. da Silveira. “Alpha Lipoic Acid in Burning Mouth Syndrome.” Journal of Oral Pathology and Medicine 38 (2009): 254-261.
Magis, D., et al. “A Randomized, Double-Blind, Placebo-Controlled Trial of Thioctic Acid in Migraine Prophylaxis.” Headache 47 (2007): 52-57.
Ziegler, D., et al. “Oral Treatment with Alpha-Lipoic Acid Improves Symptomatic Diabetic Polyneuropathy.” Diabetes Care 29 (2006): 2365-2370.
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