Daily use of antioxidants including vitamin C and vitamin E didn't improve thinking and memory skills in people with Alzheimer's disease, in a new study.
Researchers found that some patients taking antioxidants actually had faster declines in memory over the four-month study compared to those who were given vitamin-free placebo pills.
Some reports have suggested that older adults who eat a diet rich in antioxidants may have a lower risk of getting Alzheimer's disease, researchers explained. But the supplements haven't consistently been beneficial under more rigorous trials, including in those who already have an Alzheimer's diagnosis.
"Many, many people are taking these kinds of supplements with really very little scientific justification," said Dr. Ronald Petersen, head of the Mayo Alzheimer's Disease Research Center in Rochester, Minnesota.
Petersen, who has worked with the broader study group behind the new paper but wasn't involved in this research, said that many scientists still believe antioxidants may have a role in Alzheimer's disease and aging in general -- but maybe not after patients are already impaired.
"It may very well be that we have to intervene with these types of therapies much earlier," he said.
The current study included 78 patients with mild to moderate Alzheimer's disease, seen at one of 12 different medical centers. Participants were in their early 70s, on average, and were already getting treated with anti-Alzheimer's medications.
Researchers led by Dr. Douglas Galasko from the University of California, San Diego, randomly assigned the patients to one of three different supplement groups.
One-third of them took a combination of antioxidants vitamin C, vitamin E and alpha-lipoic acid daily. An additional one-third took supplements of coenzyme Q -- another antioxidant that tends to be low in people with chronic diseases. The final group took placebo pills every day.
None of the participants knew which supplements they were assigned.
Before starting patients on the supplements, and again after 16 weeks of treatment, researchers gave them tests of thinking, memory and daily functional abilities. They also tested fluid from participants' brains and spinal cords for proteins and other so-called biomarkers known to be related to brain changes in Alzheimer's disease.
Among patients taking vitamins C and E, there was a small decrease in spinal fluid markers of central nervous system damage during the study.
But those participants also had faster declines in thinking and memory test scores -- which is something to be cautious about, Petersen said.
Otherwise, there were no differences in Alzheimer's-related measures in the three groups after 16 weeks on antioxidants or placebos, including in how well they could perform daily activities, the researchers reported Monday in the Archives of Neurology.
"We think that at the very least, these drugs... would not be likely to make a substantial contribution to the treatment of established Alzheimer's disease," Galasko told Reuters Health.
"A question is whether there are more potent antioxidants that would be worth trying," he said - though it's unclear what those would be.
Galasko noted there's some tentative evidence that very high doses of certain supplements, including vitamin E, are linked to a higher risk of disease and death.
"Just because something is 'natural,' it doesn't mean that it can't have some ill effects, especially if taken at larger doses," Petersen told Reuters Health.
However, Galasko said, it's reasonable for people to take recommended amounts of vitamins and other antioxidants for general health and still hope for a possible added thinking and memory benefit.
The antioxidants in the study were provided by Vitaline Inc, a company that markets the supplements, and some of the researchers are consultants for and have received funding from pharmaceutical companies. One is the medical director at Avid Radiopharmaceuticals, which makes products involved in the diagnosis of Alzheimer's disease.
Petersen said there aren't any vitamins or other supplements that have been clearly shown to ward off Alzheimer's, or to slow disease progression in people who already have it.
"Just a regular, standard, good heart-healthy diet is probably as well as you can do right now," he said, in addition to keeping your mind and body active.