A quarter of the subjects did 35-minute sessions of walking, cycling or jogging three times a week for six months, while eating a healthy diet. These people started out with an average mental age of 93, determined by a series of thinking-skills tests. But after six months, their mental age had improved to the level of an 84-year-old. Exercise and healthy diet are thought to improve thinking skills by helping the heart work better, thereby increasing blood flow to the brain. The study, published in the journal Neurology, shows a relatively short period of lifestyle change can make a serious difference to age-related thinking problems.