Doctors have long urged people to exercise throughout their lives, pointing out that physical fitness can reduce the risk of dementia and other illnesses.
But the new research suggests physical activity can actually reverse the progress of the disease once it has taken hold.
The findings, published in the Neurology medical journal, bolster growing evidence that exercise can be used to treat cognitive problems, rather than simply being used to lower the risk many years in advance.
A clinical trial on elderly people, with an average age of 74, found those who exercise programme for an hour, three times a week, saw an improvement in overall thinking skills.
The participants’ blood pressure also improved and they were able to walk further.
But the results suggested that the benefit only lasted as long as people continued with an exercise plan.