The 4 best ways to maintain your brain

Images: Thinkstock Aerobic exercise is the best documented brain builder.

The most conclusive evidence shows that combining activities that benefit body and soul also reduces the risk of dementia.

A few decades ago, the state of your brain was believed to be beyond your control. Conventional wisdom taught that people are born with a certain number of brain cells, which die over time and are not replaced. But recent years have brought good news: although the areas of the brain associated with memory and reason shrink with age, you can add still add brain cells and build new connections between those cells throughout your life.

Dr. Bradford Dickerson, associate professor of neurology at Harvard Medical School, studies how the structure and function of brain areas involved with memory and reasoning change with age. "Many of the activities linked to a reduced risk of dementia may truly be helpful in preserving memory and reasoning," he says. The following lead the list.

1 Physical exercise. "The best evidence so far is for aerobic exercise and physical fitness," Dr. Dickerson says. Not only have scores of observational studies linked regular aerobic exercise to reduced risk of dementia, the results of several randomized controlled clinical trials and a few imaging studies indicate that aerobic exercise increases brain mass and improves reasoning ability. In studies of healthy people that showed the greatest positive effect, people got an average of 30 minutes of aerobic exercise five times a week over a year. Moreover, controlled trials in people with mild cognitive impairment showed that exercise was effective in arresting decline. There is also some evidence that mastering more complicated physical activities, like dance or sports, has greater benefits than repeating simpler ones, like walking. What the studies haven't determined is whether the benefits of exercise disappear when people become sedentary.

2 Mediterranean diet. The Mediterranean diet—high in fruits, vegetables, whole grains, and legumes; moderate in olive oil and unsaturated fats, cheese and yogurt, and wine; and low in red meat—has been a mainstay of cardiac prevention for almost 20 years. More than a dozen observational studies have shown that it is also associated with a reduced risk of dementia. In those investigations, people who adhered to the diet most closely had the greatest reduction in risk. Although the few randomized controlled trials have been too short to yield meaningful results, the diet's proven heart-healthy effects alone make it worth following.

3 Social connectedness. Evidence from observational studies linking reduced risk of dementia with social connectedness dates to the 1990s. As researchers have looked into these connections more deeply, they have discovered that variety and satisfaction in social contacts is more important than the size of a person's social network.

4 Mental stimulation. There is some evidence that challenges like playing a musical instrument or learning another language have more benefits than repetitive exercises like crossword puzzles. Although "brain-training" programs are a multi-million-dollar industry, there is no conclusive evidence that any of them improves memory or reasoning ability. "We don't know whether playing brain games is helpful," Dr. Dickerson says. "Getting together with family and friends to play cards may be as good."