The part of the brain responsible for memory shrinks twice as much in elderly people who have had a limited education, stunted social life or have not kept mentally active since they were teens, a Sydney study has found.

University of NSW researchers followed a group of 60-year-olds over three years and found that those who had been mentally and physically active continually since the age of 13 had a larger hippocampus, the part of the brain that controls short-term memory and navigation skills.

A small or atrophied hippocampus is a risk factor for Alzheimer’s and mental activity has been found to delay the onset of degenerative brain diseases, such as Huntington’s and Parkinson’s.

The author of the report, Michael Valenzuela, from the university’s school of psychiatry, said researchers had for the first time compared brains, using magnetic resonance imaging, over many years in relation to mental activity patterns, adding weight to previous work that showed that complex mental activity helped prevent dementia.

“It also helps throw some light on why there has been this consistent link between mental activity and lower dementia risk,” Dr Valenzuela said.

But he said the study, published in the Public Library of Science ONE journal, found that the size of the hippocampus was not directly related to intelligence.

“We didn’t find that a person’s IQ made much of a difference. Among the people who had the bigger hippocampi, it came down to them having a real diversity of interests,” he said. “Some had gone back to university in their 60s and 70s and others just had a variety of interesting hobbies and socialise quite a lot.”

While many drug companies were searching for ways to prevent the hippocampus shrinking, people could help themselves.

“It is vital that everyone is involved in cognitive, social and physical activities in later life such as dancing, tai chi, sailing, travelling and learning a new language, for example.”