Dementia and its evil twin, Alzheimer's, may have moved ahead of cancer on the list of most feared diseases, especially among baby boomers, who have begun to believe it is their inescapable fate if they have the bad luck to live too long.So we grasp at any news about aging, hoping that medical science has indeed found a way to preserve that most essential part of who we are - our memories.Do we protect our minds by doing The New York Times crossword puzzle or by doing aerobics? By eating more leafy greens, absorbing more vitamin D from sunshine or memorizing poetry?"There is such a thing as normal memory change with age," said Dr. Susan Lehmann, who specializes in geriatric psychiatry at Johns Hopkins Hospital, "just as there are normal changes in vision." Our brain will not always work as fast, for example, and we won't be as good at multitasking. But these are all considered normal changes, according to Lehmann.Some of our memory will not change. Our knowledge of the world, our autobiography, certain skills, such as playing an instrument. And we won't forget how to read."But it will be harder to recall specific events, harder to make new memories and remember new things," said Lehmann. "These can be annoying and they can be embarrassing, but they don't herald dementia or mean that you will have more memory problems."It is true that we will see more dementia and more Alzheimer's disease in the near future, but that has more to do with being on the cusp of a huge demographic shift. Boomers are a large group, they are getting older at the same time, and they are living longer."The expectation is that 45 percent of those will have some form of dementia by age 85 or 90," said Lehmann. "But that is not 100 percent."True, there is no cure for Alzheimer's and no treatment to significantly modify the terrible course it takes."But there is a lot of emerging research that suggests that there are things we can do as early as midlife that may have a positive impact on brain function," she said.Research has found a correlation - but not a cause and effect - between seven risk factors and their implications for the brain. Not surprisingly, Lehmann said, they are also risk factors that have implications for the heart: Diabetes, high blood pressure, obesity and smoking."A healthy heart also promotes a healthy brain," Lehmann said.The other risk factors include cognitive inactivity and physical inactivity. This is where the crossword puzzles and the daily exercise come in."No study has proven that cognitive activity prevents dementia or that lack of cognitive activity causes it," said Lehmann. "But it is possible to improve and strengthen memory at every age. It is possible to get better at it with focused approaches."It is also true, she said, that the more you use your brain, the more connections you lay down inside the brain, the more brainpower you have and the longer it takes to erode.Likewise, no study has proved that exercise can prevent dementia. But there have been studies in which women who reported the highest levels of physical activity also had the slowest cognitive decline, she said."And there have been a number of studies that show that people who are more physically active have an increased sense of well-being in general. There may be a direct benefit to the brain, as well."The most puzzling risk factor in dementia is depression, and it is of particular concern to women, who are twice as likely to suffer from depression across all ages."When someone is depressed," Lehmann said, "it slows down their ability to think and process and remember. But sometimes, depression can be a first symptom of dementia. It is a complicated relationship."Treating depression improves memory, the ability to concentrate, organize, problem-solve and all of that. Untreated depression can be a risk factor for future dementia. In any case, depression needs to be taken seriously."And finally, sleep, which becomes more elusive as we age, may have a role in all of this."Sleep often gets short shrift," said Lehmann. "Sleep is important for the consolidation of memory and fatigue degrades the ability to remember."The message might be that there will be changes in memory as we age that are as normal and stable over time as the changes in our eyeglass prescriptions. Those changes don't mean that you are condemned to forget who you are or who you love."This should be exciting and reassuring," Lehmann said. "The things that we want to do anyway, that are good for our health in general and for our sense of well-being, are also good for our brains."