The paper, which has just been published in Psychological Medicine, is the first comprehensive review of the research in the field of 'brain reserve', which looks at the role of education, occupational complexity and mentally stimulating lifestyle pursuits in preventing cognitive decline. The paper integrates data from 29,000 individuals across 22 studies from around the world.
"Until now there have been mixed messages about the role of education, occupation, IQ and mentally stimulating leisure activities, in preventing cognitive decline. Now the results are much clearer," said the lead author, Dr Michael Valenzuela, from the School of Psychiatry at UNSW. "It is a case of 'use it or lose it'. If you increase your brain reserve over your lifetime, you lessen the risk of Alzheimer's and other neurodegenerative diseases."
The key conclusion is that individuals with high brain reserve have a 46 percent decreased risk of dementia, compared to those with low brain reserve. All the studies assessed agreed that mentally stimulating leisure activities, even in late life, are associated with a protective effect.
"This suggests that brain reserve is not a static property, nor that it is determined by early life experiences such as level of education, socio-economic deprivation or poor nutrition," said Dr Valenzuela. "It is never too late to build brain reserve."
Dr Valenzuela's previous research showed that after five weeks of memory-based mental exercise, participants increased brain chemistry markers in the opposite direction to that seen in Alzheimer's disease. "The interesting point here is that this change was concentrated to the hippocampus, a part of the brain first affected in dementia," said Dr Valenzuela.
This is consistent with studies of brain reserve in mice, where some of the animals were 'hothoused' in stimulating environments. These mice had changes in the microstructure of their brains, compared with the controls.
"We now need a clinical trial to improve our neurobiological understanding of the brain-reserve effect in humans," said Dr Valenzuela. "Perhaps this could be based around mentally stimulating leisure activities that are fun."
The co-author of the paper is Professor Permider Sachdev, also from the School of Psychiatry at UNSW, who is based at The Neuropsychiatric Institute at the Prince of Wales Hospital.