Activities such as cycling and running can improve memory function and help maintain a healthy brain as we get older, according to an international study.

Researchers from Australia’s Western Sydney University and the UK’s University of Manchester examined the effects of aerobic exercise on a region of the brain called the hippocampus, which is critical for memory and other brain functions.

The brain’s health declines with age, with the average brain shrinking by approximately five per cent every decade after the age of 40.

The researchers reviewed 14 clinical trials which examined the brain scans of 737 people before and after exercise programmes.

Participants ranged from 24 to 76 years old and included healthy adults, people with mild cognitive impairments such as Alzheimer's disease, and people with mental illness, including depression and schizophrenia.

The researchers examined the effects of aerobic exercise, including stationary cycling, walking, and treadmill running. The length of the interventions ranged from three to 24 months, and from two to five sessions a week.

The results, published in the journal NeuroImage, showed that exercise reduced deterioration in brain size.

“When you exercise you produce a chemical called brain-derived neurotrophic factor, which may help to prevent age-related decline by reducing the deterioration of the brain,” said lead author and postdoctoral research fellow Joseph Firth.

“Our data showed that, rather than actually increasing the size of the hippocampus per se, the main ‘brain benefits’ are due to aerobic exercise slowing down the deterioration in brain size. In other words, exercise can be seen as a maintenance programme for the brain.”

Firth added that along with improving regular 'healthy' ageing, the results could have implications for the prevention of ageing-related neurodegenerative disorders such as Alzheimer's and dementia, however, further research is needed to establish this.