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A new study found that walking daily six to nine miles can preserve brain gray matter and prevent memory deterioration with aging.

Dr Kirk I. Erickson, from the University of Pittsburgh in Pennsylvania told the press that our brains shrink in late adulthood, and this can lead to memory problems.

Researchers have promoted the theory that physical activity helps to preserve grey matter volume in late adulthood, which in turns protects memory function, but there have not been enough studies following a sizable group of elderly people for a good number of years to back this with evidence.

Grey matter comprises mostly the cell bodies of neurons, as opposed to the axons or fibers that link them together and transmit signals.

Erickson said he and his colleagues hope their results will now prompt some "well-designed trials of physical exercise in older adults as a promising approach for preventing dementia and Alzheimer's disease".