Updated October 11, 2007

Antioxidants
Should You Supplement?

by Robert A. Jacob, Ph.D.

Some, but not all, studies have found that treating people with Type 2 diabetes with ALA improved blood glucose control and also reduced measures of oxidative stress that may contribute to diabetes complications. In one German study, people with Type 1 and Type 2 diabetes who were given 600 mg per day of ALA for 18 months had lower levels of two markers for diabetic kidney disease than a control group of people with diabetes that did not receive the ALA.

Most promising of the studies with ALA have been those that indicate benefit towards the symptoms of diabetic neuropathy. The studies have generally treated people with diabetes with 600 mg of ALA per day, either intravenously or orally, and have found improvement in both systemic and localized symptoms of neuropathy such as pain, numbness, burning sensation, foot problems, and heart rhythm problems. One specific study published in 2000 showed that both intravenous infusion and oral consumption of ALA enhanced blood vessel relaxation and improved circulation in small blood vessels in people with diabetic peripheral neuropathy. A 2004 article in the journal Treatments in Endocrinology reviewed the studies on ALA and diabetic neuropathy. The review included seven randomized clinical trials of ALA in people with diabetic neuropathy and concluded that short-term (3 weeks) intravenous infusion and long-term (4–7 months) oral consumption of ALA improved symptoms of neuropathy to a clinically meaningful degree while indicating a high safety profile for the drug.

The bottom line
Oxidative stress is strongly linked to the development of diabetes and its complications. While laboratory and animal studies show benefits from antioxidant treatments, human clinical trials of the major dietary antioxidants—vitamin E, vitamin C, and carotenoids—have been largely negative. While these natural antioxidants are generally safe, the evidence does not support their use for preventing or treating diabetic conditions. This conclusion is similar to that of the year 2000 report of the National Academy of Sciences panel on Dietary Antioxidants and Related Compounds, which states that the evidence does not warrant increased intakes of the antioxidants to protect against chronic degenerative diseases, including diabetes.

The negative findings for vitamin E, vitamin C, and carotenoids should not end the research on antioxidant protection for diabetes. Clinical trials that focus specifically on people with diabetes have not yet been conducted. Since the body limits the amount of natural antioxidants in tissue cells (including the insulin-producing pancreatic beta cells), some scientists have recently suggested that artificially created antioxidants designed to better enter the cells may provide protection against oxidative damage in people with diabetes. Others suggest that some drugs currently used to treat cardiovascular disorders, including statins, ACE inhibitors, and calcium channel blockers, provide antioxidant protection beyond their other mechanisms of action. Also, since most trials have only studied single antioxidants, studies with multiple antioxidants (such as combinations obtained from foods) should be considered. (For more information on obtaining antioxidants from foods, see “Food Sources of Antioxidants”.)

Alpha-lipoic acid has been shown to be beneficial for safely treating diabetic neuropathy, and the recent development of an oral sustained-release form holds further promise (sustained-release forms maintain more even blood levels of a drug for a longer period of time). To help determine conclusively whether ALA is effective for treating diabetic neuropathy, a large multicenter trial is being conducted in North America and Europe to assess the effects of oral treatment with ALA on the progression of diabetic neuropathy. Despite some disappointing results so far, further research holds promise for providing clinically significant antioxidant protection against diabetes and its complications.

Robert A. Jacob is a retired nutrition research scientist whose specialty is the role of antioxidants and other micronutrients in health and disease. He was a member of the National Academy of Sciences panel that set the current recommended dietary allowances for antioxidant vitamins.

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