Thinking and memory skills were most improved when people exercised the heart and muscles on a regular basis, a review of 39 studies found.
This remained true in those who already showed signs of cognitive decline.
Taking up exercise at any age was worthwhile for the mind and body, the BBC quoted Australian researchers as saying.
Exercises such as T'ai Chi were recommended for people over the age of 50 who could not manage other more challenging forms of exercise, the study in the British Journal of Sports Medicine said.
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The theory is that through exercise the brain receives a greater supply of blood, oxygen and nutrients that boost its health as well as a growth hormone that helps the formation of new neurons and connections.
In this analysis of previous studies, researchers from the University of Canberra looked at the effects of at least four weeks of structured physical exercise on the brain function of adults.
Joe Northey, study author and researcher from the Research Institute for Sport and Exercise at Canberra, said the findings were convincing enough to enable both types of exercise to be prescribed to improve brain health in the over-50s.
"Even if you are doing moderate exercise only once or twice a week there are still improvements in cognitive function, but the improvements were better the more exercise was done," he said.
Dr Justin Varney, lead for adult health and wellbeing at Public Health England, said any physical activity was good for brain and body.
"Whilst every 10 minutes of exercise provides some benefit, doing 150 minutes a week cuts the chances of depression and dementia by a third, and boosts mental health at any age.
"Doing both aerobic and strengthening exercises leads to a greater variety of health benefits," Varney said.
Dr Dean Burnett, lecturer in neuroscience and psychiatry at Cardiff University, said the study gave a clearer picture of how exercise affected the brain - but there were still issues.
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