DEAR DR. ROACH: Is there any evidence that high doses of vitamin C have decreased or prevented the risk of Alzheimer’s disease? I ask this question because none of the people I know who have developed Alzheimer’s have been taking high doses of vitamin C daily (4,000 to 6,000 milligrams). So, I wonder if this safe, inexpensive, natural remedy, found in health-food stores, could have stopped these tragedies by preventing atherosclerosis in the brain. -- A.S.

ANSWER: Many people have had the same idea, and it has been the subject of scientific study. A recent review of the many studies that have been done shows that a diet rich in vitamin C (and other nutrients) is of benefit in helping prevent dementia (including Alzheimer’s). However, taking supplements, even high-dose supplements, is unlikely to have any additional benefit over a healthy diet. Most of the studies showed no benefit of vitamin C compared with placebo. I don’t recommend vitamin supplementation for the purposes of preventing Alzheimer’s disease.

The booklet on Alzheimer’s disease gives a detailed presentation of this common illness.