Regular exercise in old age could keep the mind young, a series of studies have found.
Evidence is growing that fitter people have bigger brains and better memories, with experts saying that "what is good for the heart is good for the head".
Keeping fit may even trigger the growth of up to three times as many new cells in the brain's memory hub - the hippocampus - helping protect against Alzheimer's disease, according to America's National Institutes of Health.
Brain scans on those in their 50s and 60s showed that blood flow to the brain - and so the supply of oxygen and vital nutrients - was higher in those who were fitter, said the University of Kentucky.
Even a brisk walk is beneficial, with the University of Pittsburgh finding that going for a stroll three times a week boosted the size of the hippocampus and other key brain regions by up to 2 per cent.
This is equivalent to taking two years off the brain's age, according to the journal NeuroImage.