As if you needed another reason to exercise, a recent study indicates that being physically fit in midlife can lower the risk of dementia. The fitness levels of nearly 20,000 adults were studied over a 24-year period, most of whom were men and women in their 40s and 50s. Those that exercised regularly were found to have a 36 percent reduced risk of developing dementia. The physical activity guidelines, recommended by the Centers for Disease Control and Prevention, call for 150 minutes per week, or about 30 minutes a day, of moderate-intensity exercise, such as brisk walking, or 75 minutes a week of vigorous aerobic activity or an equivalent combination of the two. Even people who are past midlife can still make changes. It’s never too late to reap the health and cognitive benefits of exercise.