No one knows for sure which measures can prevent Alzheimer's disease. While it tends to run in families, you won't necessarily develop it.
If you are concerned, however, about the possibility that you might eventually develop Alzheimer's disease, your best strategy is to maintain a healthy lifestyle: Eat right and exercise regularly to keep your entire body healthy.
Although often touted to prevent Alzheimer’s, there is no evidence to suggest that the intake of antioxidants (vitamin E, beta-carotene, flavonoids, vitamin C) can prevent Alzheimer’s disease. At this point, the data supporting the use of vitamins D, B6, B12, and folate are not sufficiently clear to recommend supplementation.
Low cholesterol, low-fat diets rich in fish and omega-3 fatty acids, and high intake of fruits and vegetables may be helpful in the prevention of dementia.
Although there is some evidence that light to moderate alcohol use may be protective against dementia, the results have been inconsistent. The harmful effects of alcohol probably outweigh the benefits.
It may be useful to participate regularly in mentally stimulating tasks like reading, crossword puzzles, or going to the museum. The concept of what is good for the heart is good for the head also applies. Controlling blood pressure and cholesterol may also decrease your chances of developing Alzheimer's disease.
SOURCES: American Association of Family Physicians. Alzheimer's Foundation of America. The Food and Drug Administration. American Federation of Aging Research. American Health Assistance Foundation. Centre for Neuro Skills. Office of Dietary Supplements. Peter Doskoch, "Brain injury and Alzheimer's Disease: What is the Link," Neuropsychiatry Reviews, October 2000.