Without a sound mind and good health, what else have you got? Exercise every day, and you're more likely to keep your mind sharp well into old age. Staying physically fit throughout your life is not only good for your body, but also it's the perfect prescription for your mind and memory. Researchers from the V.A. Medical Center in San Francisco found that adults who were the most fit at the start of a six-year study maintained their mental sharpness over time and did better in tests of their mental function conducted years later than did their less physically fit peers, reports Reuters. "Physical activity appears to be good for the brain as well as the body," study author Dr. Deborah E. Barnes, told Reuters. "Older adults with higher levels of cardiorespiratory fitness experience a slower rate of cognitive decline over time." The experiment: Cardiorespiratory fitness reflects how well the heart and lungs process oxygen during exercise. In this study, the researchers gave 349 adults aged 55 and older a treadmill test to measure their cardiorespiratory fitness, as well as a mental function test that required them to register and recall words and follow instructions. No one had any symptoms of cardiovascular disease, physical disability, or mental impairment at the start of the study. The results: Those who were most fit at the beginning of the study were also the least likely to experience mental decline over the six-year period, while those who were the least fit were also more likely to suffer a mental decline as time went on. Why? A person who has cardiorespiratory fitness may also be at a lower risk for cardiovascular disease, high blood pressure, and diabetes, all of which are known to be associated with poor mental function in older adults. In addition, cardiorespiratory fitness may be directly associated with blood flow in the brain. Reduced blood flow to the brain has been linked to lower mental function in both Alzheimer's disease patients and normal older adults, reports Reuters. The study findings were published in the Journal of the American Geriatrics Society.