Researchers have suggested that antioxidants might help thwart Alzheimer's disease, but a new study finds that a "cocktail" of vitamins E, vitamin C and alpha-lipoic acid has no effect on certain indicators of the brain disorder.
The supplements may even have hastened mental decline, the researchers said.
"The benefit on oxidative stress in the brain was small and is of unclear significance," said lead researcher Dr. Douglas Galasko, a professor in residence in the department of neurosciences at the University of California, San Diego.
"Patients did not show cognitive improvement in this short-term study; in fact, there was a slight worsening on one test of cognition in patients who received the antioxidant combination," Galasko said.
Aging causes oxidative damage in the brain, which is extensive in people with Alzheimer's disease. Clinical trials looking at whether a diet rich in antioxidants could reduce that risk have had mixed results, the researchers said.
This study does not support using any of these antioxidants once a diagnosis is made of established Alzheimer's disease, Galasko said. "If antioxidants continue to be tested against Alzheimer's disease, newer approaches or drugs may be needed," he said.
How the study was done
This study, published in the online edition of the Archives of Neurology, does not address whether taking antioxidants could help to prevent Alzheimer's disease, he noted. Alzheimer's disease is the most common form of dementia among older people.
For the study, Galasko's team gave antioxidant supplements to 78 patients with Alzheimer's disease who were part of a study funded by the US National Institute on Aging. The patients were placed into three groups. One group received daily doses of vitamin E, vitamin C and alpha-lipoic acid. A second group was given coenzyme Q (a compound made naturally in the body to protect cells from damage) three times a day. The third group received a placebo. After 16 weeks, 66 patients had their cerebrospinal fluid analysed.
Among the three groups, the researchers found no difference in markers related to Alzheimer's disease in the cerebrospinal fluid. These markers included the amyloid-beta protein and the proteins tau and P-tau.
Galasko's group did see lower levels of one marker called F2-isoprostane, which could indicate a reduction in oxidative stress in the brain. However, the use of vitamins might have increased the pace of the disease, causing faster decline in mental ability, they cautioned.
Greg Cole, associate director of the Alzheimer's Disease Research Center at the University of California, Los Angeles David Geffen School of Medicine, said that vitamin E alone has shown some limited benefits in Alzheimer patients, but with no evidence that it really works to reduce oxidative damage, and that alpha lipoate - a form of alpha-lipoic acid - alone has also had some reported benefits, he said.
What the study found
"Unfortunately, these researchers found no impact on pathological protein levels, and in their small group of patients, their cognitive function actually declined more than in the placebo group," Cole noted.
The increased cognitive decline might be due to random variation, he said, "or it may be a surprising but real adverse effect from something as seemingly innocuous as an antioxidant cocktail."
His research group has seen similar adverse effects from some, but not all, antioxidant mixes, he said.
"This should be a caution to the supplement manufacturers who typically sell products throwing in some mix of what seems like a great group of sensible antioxidants," he added. "Everyone assumes that they will work well together and are good for you, but they don't test them."
Looking after your loved one
For more information on Alzheimer's disease, visit the Alzheimer's Association.
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