People who exercise later in life may better protect their brain from age-related changes than those who do not, a study suggests.

Researchers found that people over 70 who took regular exercise showed less brain shrinkage over a three-year period than those who did little exercise.

Psychologists and Neuroimaging experts, based at the University of Edinburgh, did not find there to be any benefit to brain health for older people from participation in social or mentally stimulating activities.

Greater brain shrinkage is linked to problems with memory and thinking and the researchers say their findings suggest that exercise is potentially one important pathway to maintaining a healthy brain both in terms of size and reducing damage.

The researchers also examined the brain's white matter - the wiring that transmits messages round the brain. They found that people over 70 who were more physically active had fewer 'damaged' areas - visible as abnormal areas on scanning - in the white matter than those who did little exercise.

Additionally, the researchers from the University of Edinburgh found that the over-70s taking regular exercise had more grey matter - the parts of the brain with nerve cell bodies.

The Edinburgh team used MRI scans to measure the volume of brain tissue and the volume and health of the brain's white matter in almost 700 people.

They studied levels of physical activity which ranged from moving only for necessary housework to more strenuous forms of exercise such as keep-fit or taking part in competitive sports.

Scientists also recorded whether or not the participants - all aged over 70 - took part in mentally stimulating activities such reading and participating in social groups.

Dr Alan Gow of the University of Edinburgh's Centre for Cognitive Ageing and Cognitive Epidemiology who led the research, said: "Our results suggest that to maintain brain health, physical activity may be more beneficial than choosing more sedentary activities. We are excited by the next stages of this research as we seek to understand more about what might underlie the effect, but in the meantime, increasing physical activity - even a short walk each day - can only be encouraged."

Professor James Goodwin, Head of Research at Age UK who fund the Disconnected Mind research project, said: "This research is exciting as it provides vital clues as to what impacts the way our brain ages and how we could tackle mental decline. If we can establish definitively that exercise provides protection against mental decline, it could open the door to exercise programmes tailored to the needs of people as they age.

"We already know that exercise is important in reducing our risk of some illnesses that come with ageing, such as cardiovascular disease and cancer. This research reemphasises that it really is never too late to benefit from exercise, so whether it's a brisk walk to the shops, gardening or competing in a fun run it is crucial that, those of us who can, get active as we grow older."